Hi all,
Wondering if anyone can offer advice on a strange issue I'm having. My old banger runs very well and pulls fantastically for its age and mileage, but if you go from about 75% throttle to full throttle, you can feel the engine holding back. The car idles and runs perfectly the rest of the time, it's just at full chat that it seems to struggle.
My first thought is the throttle position sensor, but I'm not sure on the procedure for testing it if that is even the issue.
Could someone with far more knowledge than me offer any suggestions?
Is it slower at 100% than at 75%? Or just not 25% more?
Any popping and banging or does it just go soft?
Do you have Torque pro? Does the MAF values look reasonable going from 75% to 100%?
Quote from: jonbill on May 1, 2018, 05:21
Is it slower at 100% than at 75%? Or just not 25% more?
Any popping and banging or does it just go soft?
Do you have Torque pro? Does the MAF values look reasonable going from 75% to 100%?
Yes, that's a better way of putting it - It is slower at 100% than at 75-80%. It just goes soft at full throttle.
The only other symptom is if you change gear quickly from say 1st to 2nd - if you get back on the throttle too quickly, it kangaroo's briefly like the throttle can't keep up. Other than that it is fine and runs perfectly.
I do have Torque Pro but I'm not sure what the test should look like (I've never had to delve too deep into the app)- presumably a smooth-ish graph from partial to full throttle?
Any help truly appreciated!
It does sound like it might be overfueling.
I would expect as you say a smooth progression on the MAF as you go from 75% on up. Might have to get someone to test a normal one.
A couple of other things to maybe look at:
1. Ignition timing over the range. I wouldn't expect it to change much - should be low 30s I think.
2. Whether it is switching from closed loop to open loop when it degrades.
3. What the fuel trims are saying before it goes to open loop.
All these things are done by adding gauges in 'realtime information'
Do you have an ODB reader to check the fuel trims? Might be worth doing an ECU reset - could also be a dirty MAF.
Sounds like vvti to me. Or maf
Cleaning the MAF is pretty much always the first port of call anyway
Thanks for all of the advice so far everyone!
The MAF has been cleaned (although I guess that's no guarantee to it working properly) and you can clearly feel the VVTi smoothly switch over - it's still decently rapid up until you floor it completely then it just drops off slightly. It still accelerates, just at a diminished rate.
The battery was disconnected over the winter so the ECU will have reset, but it's still the same. I have checked for any historic codes when I first got the car - nothing in there and no reoccurring EMLs.
The car never smells fuelly either - to be honest, other than this slight issue, it really does run very well indeed.
It does sound like it's time to find my ODB and grab some readings. OK to post them on here? It's not my particular area of expertise (because I don't have any areas to be honest) so I may need some guidance about what I'm seeing from clever people! :D
Could the cat be blocked/choked or an obstruction in the airbox etc?
Just throwing them out there, I'm far from expert but it sounds like it's struggling to breathe wide open?
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Yes interested to see what you get out of the OBD.
Another quick check: it is throttle opening that's affecting things, not revs right? Peak power I bet is around 5500 so if you're pushing it much beyond there it does go downhill.
Quote from: Call the midlife! on May 1, 2018, 09:16
Could the cat be blocked/choked or an obstruction in the airbox etc?
Just throwing them out there, I'm far from expert but it sounds like it's struggling to breathe wide open?
Sent from my iPhone using Tapatalk
That was my next guess as well, choked.
Mine has a similar effect since removal of pre-cats to be honest. My theory being that at full load the precat chambers cause a bottleneck on flow and creates back pressure, resulting in a noticeable flattening of power at high load. Further visible by an identically setup car with an aftermarket manifold pulling away at the top end.
So, same theory holds for blocked cat or congested air filter. A clean air filter really can be night/day.
Especially the bumpiness you mention sounds a lot like it can't get enough air in at closed throttle. The IACV is a tiny hole and if the filter is restricted you're starving the car.
Fuel smell doesn't happen too often in a stock mr2 as the ecu is absolutely magical at the way and speed it adjusts fueling.
Quote from: jonbill on May 1, 2018, 09:21
Yes interested to see what you get out of the OBD.
Another quick check: it is throttle opening that's affecting things, not revs right? Peak power I bet is around 5500 so if you're pushing it much beyond there it does go downhill.
Yep, it's the throttle opening that affects it - I've not really gotten around to ringing the engine out - it's quite a torquey lump so I've not yet had the need! When I get a chance to get out for some tests, I'll record some data and see what is what!
Quote from: Call the midlife! on May 1, 2018, 09:16
Could the cat be blocked/choked or an obstruction in the airbox etc?
Just throwing them out there, I'm far from expert but it sounds like it's struggling to breathe wide open?
Sent from my iPhone using Tapatalk
Quote from: shnazzle on May 1, 2018, 10:18
That was my next guess as well, choked.
Mine has a similar effect since removal of pre-cats to be honest. My theory being that at full load the precat chambers cause a bottleneck on flow and creates back pressure, resulting in a noticeable flattening of power at high load. Further visible by an identically setup car with an aftermarket manifold pulling away at the top end.
So, same theory holds for blocked cat or congested air filter. A clean air filter really can be night/day.
Especially the bumpiness you mention sounds a lot like it can't get enough air in at closed throttle. The IACV is a tiny hole and if the filter is restricted you're starving the car.
Fuel smell doesn't happen too often in a stock mr2 as the ecu is absolutely magical at the way and speed it adjusts fueling.
From when I changed the manifold over, the general state of the exhaust (ports, precats etc) seemed really very good, so I'd be surprised if it was the main cat, but the air-filter is a possibility - I ordered a Blitz panel filter last night as it happens, so I will be able to eliminate/prove that soon enough! It's had quite a good service life up until the owner before me who did very few miles so didn't bother servicing it. I did give the current filter a cursory inspection and it was just about OK, but then they can still be badly blocked with contaminants.
Once again, thanks for all of the suggestions - some knowledge is a lot better than just flinging new parts at a car and hoping it sorts it. It's certainly less expensive!
Found my OBD and had a quick play around on the drive. It seems I can rule my suspicion of the throttle position sensor out - it reads smoothly across the full length of the pedal travel up to 78% which I understand is correct.
There is a MAF reading in there as well - just the one so I'm guessing I'll need to be looking at that as well?
I will say that on the other settings, I'm not sure which details I should be measuring. Fuel trim long term bank 2 hurgle schmurgle....I'm a bit lost...
Yeah that MAF one.
There are short term and long term trims for bank 1 and 2. Bank 1 is the cylinders that go with the right o2 sensor.
If everything is perfect, your long term trims will be zero and your short term trims will oscillate between -5 and +5 or so, while the ECU enriches and leans it out a little to check the reaction from the o2 sensor and make sure everything is working.
In practice, your long term trims may be non zero as the engine has learned to deal a little air leak or maybe aging o2 sensors.
So thats all good when your ecu is in closed loop mode which means it's constantly adjusting the trims to Keep the AFR stoichiometric.
When you give it the beans it can't keep up with that so it just uses a fixed fueling map based on MAF, TPS and temp values (poss more, I'm sure the others will chip in). Thats open loop mode.
Open or closed loop mode is another thing Torque can read and show you.
I imagine you're going to be open loop when you go full throttle, that's why MAF etc values are worth looking at there
(Also on that note, might be worth checking sensible values for coolant temp: it'll add fuel if it thinks the engine is cold)
Ah right, so if I put together a screen with the fuel trims, MAF, throttle position and closed/open loop, that should give me the info required?
Sorry for being dim - I've only ever used it for logging and resetting fault codes.
Yeah thats the sort of thing.
Cheers jonbill - I'll be changing the plugs and airfilter at the weekend after which I'll give it a go and see what comes about. Thanks for all the help! :notworthy:
T A B
Trims and MAFs are like when you have a check up, Heart rate, blood pressure, oxy saturation.
A very good window into whats going on inside.
Very good vid here plus part 2
https://www.youtube.com/results?search_query=secret+of+engine+problem+diagnosis-+fuel+trims+pt.1 (https://www.youtube.com/results?search_query=secret+of+engine+problem+diagnosis-+fuel+trims+pt.1)
78% seems a bit low to me tbh.
I could be wrong but I think 88% was my max.
I'll have a look tomorrow. Also, here is my torque layout. Might help. It's designed for landscape
You can import it
https://drive.google.com/file/d/1MwlIhWyDYqNHagMHGZm4iwdOiJnUusVt/view?usp=drivesdk
Quote from: Ardent on May 1, 2018, 21:34
T A B
Trims and MAFs are like when you have a check up, Heart rate, blood pressure, oxy saturation.
A very good window into whats going on inside.
Very good vid here plus part 2
https://www.youtube.com/results?search_query=secret+of+engine+problem+diagnosis-+fuel+trims+pt.1 (https://www.youtube.com/results?search_query=secret+of+engine+problem+diagnosis-+fuel+trims+pt.1)
I have to admit to thinking that vid would be well over my head, but it's actually very good at explaining it all. I'll pick up on part 2 when it's not gone midnight!
Quote from: shnazzle on May 1, 2018, 21:58
78% seems a bit low to me tbh.
I could be wrong but I think 88% was my max.
I'll have a look tomorrow. Also, here is my torque layout. Might help. It's designed for landscape
You can import it
https://drive.google.com/file/d/1MwlIhWyDYqNHagMHGZm4iwdOiJnUusVt/view?usp=drivesdk
Cheers for the layout - I've grabbed and imported.
Torque really was worth the pittance I paid for it all those years ago. It's saved me so much money over the years. One of the best tools you can get.
The TPS is at least linear over the length of the throttle, so I think it's OK, but your reading would be a great comparison.
Every day is a school day!
https://youtu.be/hpA2jWCfVjc
Ignore my fueling. My maf calibration is off. The joys of an aftermarket intake.
TPS goes from 11 to 84
Cheers for that! Mine is also 11 at rest but peaks at 78 - but I suspect that the fact that it's linear is probably key. I was looking for it to rise steadily until around 80% throttle travel and then start backing off beyond that due to a fault, but it increases across the length of the pedal. The six % difference I suppose could be down to adjustment of the throttle cable which I will check.
Curiouser and curiouser....
I have yet to log the various stats of my car, but yesterday, I replaced the spark plugs and the air filter then clapped my hands for a job well done and got on the beers at a BBQ. Today, I took it out for a test drive and it's not a happy banger!
At a guess, I'd say it's now down by about 30bhp and a load of torque throughout the rev range. It's as flat as a pancake like the previous wide open throttle issue but at all throttle openings. Along with this, going from part to full throttle quickly results and a large misfire and a lot of stuttering. I seem to have angered the MR2 Gods!
Going through things disturbed - coils (look like the original ones) plugs (obviously - these are the correct ones for the car), air intake (a lot of wiggling to get the air box lid off) and the battery (removed to change the gearbox oil) so a ECU reset in effect.
My initial thoughts are a coil being on the way out or the intake hose has a split that I can't see.
I realise that identifying and fixing faults on the internet is like nailing ideas to a Frisbee and throwing them over a rainbow, but any ideas on what to check next or what a failing coil would do would be great!
Annoyingly, no fault codes showing!
I'd look at the o2 sensor readings and the fuel trims. That behaviour sounds like it's lean.
Have you tried putting the plugs back? Your sure they are the right plugs?
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Sounds like you may have created an air leak on the input side while messing with the airbox. Could be loose at the throttle body?
Also, having wobbled that lot around a bunch the MAF may have got dirty, or (if it was a bit dodgy already), the activity might have terminated its usefulness.
Maf issues often don't exhibit codes or warning lights.
Quote from: jonbill on May 6, 2018, 21:52
I'd look at the o2 sensor readings and the fuel trims. That behaviour sounds like it's lean.
In all honesty I ran out of time over the bank holiday and just dumped it down the drive until I can find the time to take a look, but I'll finally do a run out to get some readings this week.
Quote from: Smcknighty on May 7, 2018, 21:51
Have you tried putting the plugs back? Your sure they are the right plugs?
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Pretty sure - they were ordered from MR2-Ben and they seem to know their stuff, but I will be going over the work I did to double check everything.
Quote from: Carolyn on May 8, 2018, 08:47
Sounds like you may have created an air leak on the input side while messing with the airbox. Could be loose at the throttle body?
Also, having wobbled that lot around a bunch the MAF may have got dirty, or (if it was a bit dodgy already), the activity might have terminated its usefulness.
Maf issues often don't exhibit codes or warning lights.
Well that could well be it I suppose, it was cleaned last year and is the original but yes it did get a fair bit of rattling around refitting the airbox. As you say, there's no codes showing and it's showing very similar symptoms of a friends Alfa when that went bandy. ODB readings will hopefully show the issue though!
Thanks for the suggestions folks! Will update the thread when I have more info.
Not sure about this car but the test on my Alfa was to unplug the Maf and see if it runs better. It will throw a code but should guess values using the o2 sensors and run better is the theory I think
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Quick update on this. So far I've swapped in the old plugs, slapped in a new MAF, removed the intake pipe checked for leaks and refitted, but I've still got the same problem unfortunately.
jonbill has been very kind taking a look at my logged data, but so far it's really inconclusive.
From my latest reading, the long term fuel trims are at around -14% at idle and smooth off to around 0 at 2500rpm (I didn't go much over that on my drive as the neighbours are lovely and I don't want to pee them off). Very odd indeed....
Vacuum leak. Pcv hose? Evap hose?
Checked most of this out today and it all looks in remarkable (for 120,000 miles) shape. I am genuinely flummoxed.
A great word 'flummoxed' - I may have to start using it more.
So the situation is that the LTFT is running very negative at idle, improving to 0% at 2500rpm and the engine runs OK in this rev range? (That suggests it's running rich at idle so not likely to be an air leak.) It's then only at higher revs that the engine starts to run poorly.
The fuel trims at higher revs when the problem shows up would be very interesting to see.
Could it be an injector that is stuck at one particular flow rate, this could make the engine run rich at low revs but then lean at high revs? It could be that it gets so lean at high revs that the fuel trims can't compensate sufficiently which is why the engine is holding back.
Quote from: lamcote on May 13, 2018, 20:33
So the situation is that the LTFT is running very negative at idle, improving to 0% at 2500rpm and the engine runs OK in this rev range? (That suggests it's running rich at idle so not likely to be an air leak.) It's then only at higher revs that the engine starts to run poorly.
The fuel trims at higher revs when the problem shows up would be very interesting to see.
Could it be an injector that is stuck at one particular flow rate, this could make the engine run rich at low revs but then lean at high revs? It could be that it gets so lean at high revs that the fuel trims can't compensate sufficiently which is why the engine is holding back.
I did a full road run with it, but the info was very hard to determine. If you're interested, you can take a look here - https://docs.google.com/spreadsheets/d/12S4ND_ywoG-hUfr-uLAaa2XolusrrEDM8J6JjM5Z6_Y/edit?usp=sharing (https://docs.google.com/spreadsheets/d/12S4ND_ywoG-hUfr-uLAaa2XolusrrEDM8J6JjM5Z6_Y/edit?usp=sharing)
I admit this is all unknown territory for me!
I only seem to be able to get a .pdf version of that, it would be handy to get the actual spreadsheet so I can manipulate the data. Is there a way to get that from your link?
Not convinced your o2 sensors are kosher. Particularly bank2. (left)
On that spreadsheet there are 4 columns for Bank 1 fuel trims (columns F, G, H, I) and 3 columns for Bank 2 trims (J, K, L), not sure why, can anyone tell me and also confirm which columns are the useful ones?
Quote from: lamcote on May 13, 2018, 21:04
I only seem to be able to get a .pdf version of that, it would be handy to get the actual spreadsheet so I can manipulate the data. Is there a way to get that from your link?
Is this any better - https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing (https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing)
Quote from: shnazzle on May 13, 2018, 21:19
Not convinced your o2 sensors are kosher. Particularly bank2. (left)
There was one that was showing voltage completely out of line with the others, but no EML at all. I just assumed that the o2 sensors were pretty good at triggering a fault in the ECU.
Quote from: The Arch Bishop on May 13, 2018, 23:34
Quote from: lamcote on May 13, 2018, 21:04
I only seem to be able to get a .pdf version of that, it would be handy to get the actual spreadsheet so I can manipulate the data. Is there a way to get that from your link?
Is this any better - https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing (https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing)
Quote from: shnazzle on May 13, 2018, 21:19
Not convinced your o2 sensors are kosher. Particularly bank2. (left)
There was one that was showing voltage completely out of line with the others, but no EML at all. I just assumed that the o2 sensors were pretty good at triggering a fault in the ECU.
That'll be your bank1s2 (post-cat). It tends to read pretty flat. If it's tracing your bank 1s1 and 2s1 then your cat is knackered. So at least you know your car works.
As for the rest;
It's adding a fair bit of fuel. Running a fair bit (15-18%) lean across the load range.
That could be a measuring issue (duff o2), incorrect maf reading (aftermarket intake), or still air leak.
What it doesn't explain is why your throttle refuses to exceed 78 and your MAF 66 at over 5.5k rpm. That should be in the high 80s at least.
So if you piece it together; maf says value 66 (low) and ecu fuels to 66. Gets to o2 sensors and they're saying lean. So somewhere between maf and injectors the parameters changed. Air leak may have gotten in and added mode air so now there's too little fuel.
Run lean at max rpm and the car will retard timing based on the knock sensor and o2 readings.
That could be the loss of power.
Quote from: shnazzle on May 14, 2018, 01:21
Quote from: The Arch Bishop on May 13, 2018, 23:34
Quote from: lamcote on May 13, 2018, 21:04
I only seem to be able to get a .pdf version of that, it would be handy to get the actual spreadsheet so I can manipulate the data. Is there a way to get that from your link?
Is this any better - https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing (https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing)
Quote from: shnazzle on May 13, 2018, 21:19
Not convinced your o2 sensors are kosher. Particularly bank2. (left)
There was one that was showing voltage completely out of line with the others, but no EML at all. I just assumed that the o2 sensors were pretty good at triggering a fault in the ECU.
That'll be your bank1s2 (post-cat). It tends to read pretty flat. If it's tracing your bank 1s1 and 2s1 then your cat is knackered. So at least you know your car works.
As for the rest;
It's adding a fair bit of fuel. Running a fair bit (15-18%) lean across the load range.
That could be a measuring issue (duff o2), incorrect maf reading (aftermarket intake), or still air leak.
What it doesn't explain is why your throttle refuses to exceed 78 and your MAF 66 at over 5.5k rpm. That should be in the high 80s at least.
So if you piece it together; maf says value 66 (low) and ecu fuels to 66. Gets to o2 sensors and they're saying lean. So somewhere between maf and injectors the parameters changed. Air leak may have gotten in and added mode air so now there's too little fuel.
Run lean at max rpm and the car will retard timing based on the knock sensor and o2 readings.
That could be the loss of power.
So what would you be looking at investigating with all of this? O2 sensor, TPS, or something else? I wpould have thought that any issue with the O2 sensor would have thrown an EML, but there's still nothing on that front.
Trying to describe what the car feels like is really difficult. there's clearly no torque down in the rev range (or anywhere in fact). Fast throttle changes gives you a hiccup or two before it surges slightly. A part throttle at about 3000rpm makes it stutter slightly for two or three seconds then it surges.
I realise you're probably all pretty bored of this by now... would be great to get it working before the really decent weather kicks in, but I don't want to go down the route of swapping everything out at huge cost. A bit skin-flinty of me, but I've been down that route before!
Quote from: The Arch Bishop on May 14, 2018, 23:07
Quote from: shnazzle on May 14, 2018, 01:21
Quote from: The Arch Bishop on May 13, 2018, 23:34
Quote from: lamcote on May 13, 2018, 21:04
I only seem to be able to get a .pdf version of that, it would be handy to get the actual spreadsheet so I can manipulate the data. Is there a way to get that from your link?
Is this any better - https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing (https://drive.google.com/file/d/14ILWz2BK84yMZfYgfmpAAAx1edHNn4Lw/view?usp=sharing)
Quote from: shnazzle on May 13, 2018, 21:19
Not convinced your o2 sensors are kosher. Particularly bank2. (left)
There was one that was showing voltage completely out of line with the others, but no EML at all. I just assumed that the o2 sensors were pretty good at triggering a fault in the ECU.
That'll be your bank1s2 (post-cat). It tends to read pretty flat. If it's tracing your bank 1s1 and 2s1 then your cat is knackered. So at least you know your car works.
As for the rest;
It's adding a fair bit of fuel. Running a fair bit (15-18%) lean across the load range.
That could be a measuring issue (duff o2), incorrect maf reading (aftermarket intake), or still air leak.
What it doesn't explain is why your throttle refuses to exceed 78 and your MAF 66 at over 5.5k rpm. That should be in the high 80s at least.
So if you piece it together; maf says value 66 (low) and ecu fuels to 66. Gets to o2 sensors and they're saying lean. So somewhere between maf and injectors the parameters changed. Air leak may have gotten in and added mode air so now there's too little fuel.
Run lean at max rpm and the car will retard timing based on the knock sensor and o2 readings.
That could be the loss of power.
So what would you be looking at investigating with all of this? O2 sensor, TPS, or something else? I wpould have thought that any issue with the O2 sensor would have thrown an EML, but there's still nothing on that front.
Trying to describe what the car feels like is really difficult. there's clearly no torque down in the rev range (or anywhere in fact). Fast throttle changes gives you a hiccup or two before it surges slightly. A part throttle at about 3000rpm makes it stutter slightly for two or three seconds then it surges.
I realise you're probably all pretty bored of this by now... would be great to get it working before the really decent weather kicks in, but I don't want to go down the route of swapping everything out at huge cost. A bit skin-flinty of me, but I've been down that route before!
Not bored at all.
O2 sensors don't really throw codes unless they lose all or some connectivity.
All the other codes are to do with how the ecu perceives the signals and if it's within tolerance.
If the o2 sensors drop voltage and are reading 15% leaner than 0, then the ecu has no choice but to believe it and fuel accordingly. It'll fuel to the new 0 position, which is 15% too low, and think all is fine. In the meantime the car runs like crap. It might detect misfires and adjust timing.
So another handy metric is the timing advance at idle. Should be pretty dead on 14.5 to 15.
If it's higher, it's rich with no fueling anomalies detected. (more fuel takes longer to burn so has to be ignited earlier)
If it's lower, it's lean with no fueling anomalies detected. (opposite of rich obviously. Burns very quickly so timing is delayed).
Again, whether or not there are actually fueling issues is another matter but the ecu thinks there aren't.
Anyway, back to your car :)
Throttle position senser does sound suspect. Easy test; Unplug it and see if it changes. If not, there's your issue.
The hesitance on quick throttle is definitely something that happens when the tps isn't connected or not working
Just unplug it and rev the engine from the throttle body, see if behaves differently plugged and unplugged
Cheers Shnazzle, I really do appreciate the help. A few things to test then. I'll log with the tPS unplugged and see how that goes. Sorry, that means further waffle from me!
Quote from: The Arch Bishop on May 14, 2018, 23:44
Cheers Shnazzle, I really do appreciate the help. A few things to test then. I'll log with the tPS unplugged and see how that goes. Sorry, that means further waffle from me!
Wouldn't worry about it. Keeps me off the streets and I enjoy it.
Wish I could get my hands on it haha.
By the by, unplugging the tps is a handy Toyota trick to force it into open loop (never read from o2 sensors), so if you drive the car until its at operating temp, then reset the ecu (Unplug battery for 20 mins), Unplug tps and drive around the block, you're driving purely on the fueling tables as from factory. Your timing advance will be all over the place but it helps highlight a potential culprit.
The usual suspects have all been covered;
- dirty/faulty maf
- evap pipe unplugged (pipes that come into and out of the blue actuator on the top of the intake
- intake pipe leaks after the maf (hose not tight on throttle body)
- pcv hoses connected
- air filter refresh. sometimes looks deceive. Looking a bit dirty could mean utterly blocked in real terms
- exhaust blockages (cat broken)
-
OK, well I tried going for a drive after pulling the TPS plug (sorry no resetting ECU etc), but from the drivers seat, there was an obvious pause between off-on throttle (junctions were interesting) and strangely a little more power (but certainly not full power), but there was no missing or kangarooing and it actually felt smoother. Also gone was the mid throttle 2-second throat-clearing and surge.
Basically, once on throttle, it was smooth if gutless with no missing.
Soooo.... should I indeed be in the market for a replacement TPS?
Quote from: The Arch Bishop on May 15, 2018, 19:57
OK, well I tried going for a drive after pulling the TPS plug (sorry no resetting ECU etc), but from the drivers seat, there was an obvious pause between off-on throttle (junctions were interesting) and strangely a little more power (but certainly not full power), but there was no missing or kangarooing and it actually felt smoother. Also gone was the mid throttle 2-second throat-clearing and surge.
Basically, once on throttle, it was smooth if gutless with no missing.
Soooo.... should I indeed be in the market for a replacement TPS?
OK narrowing it down then.
Never heard of a tps fail so let's have a think...
TPS does seem to be responding right? I.e. Torque pro is logging tps values in line with your input.
They're just oddly low values.
The hesitation at first opening without the tps connected is fully expected. The car doesn't know you're trying to set off so it's not doing its usual acceleration enrichment. It's playing catch-up once it starts to see maf values and rpm go up.
Now there's two things the car is no longer reading from; tps and o2 sensors.
Given the history of these cars, it does sound suspiciously like o2.
So that'd be my first bet. Depending on the age of the car, I'd be tempted to just go big and replace all 3. They all affect fueling, contrary to what a lot of people think.
Current funds dictate that all three is beyond my means especially as I'd only buy the Denso ones after a bad experience with a cheapy. I'll look to get one of the the manifold ones and swap it out in the hopes of curing it. Which means of course that it'll end up being the post-cat one! ;D
Quote from: The Arch Bishop on May 15, 2018, 21:00
Current funds dictate that all three is beyond my means especially as I'd only buy the Denso ones after a bad experience with a cheapy. I'll look to get one of the the manifold ones and swap it out in the hopes of curing it. Which means of course that it'll end up being the post-cat one! ;D
Ok, different idea. I've got a bag of o2 sensors. Some good, some not good. The not good ones primarily due to heater circuit.
I'll do a quick resistance check on them and send some over.
You may get a heater circuit engine light, but for the purposes of narrowing down your issues, it doesn't matter.
Pm me your address details and I'll get them in the post asap
That's ridiculously good of you and I'd be very grateful. I'll send you a PM.
So I've packaged things up for you.
A veritable fun pack of analysis.
You will find
- 2 o2 sensors. Sorry, no long (cat) one in my arsenal. But process of elimination should make it unnecessary.
- one TPS
- one MAF
Start with the o2 sensors (their heater circuits are broken so expect codes), reset the ecu and try it out.
Then maf, as it's easy. Again, reset ecu.and try
Then tps
That seems a reasonable plan of attack, although my money is on the TPS - I think it's the only thing the ECU has that enables it to see changes in demand instantly, and that's where the symptoms are. I think.
i.e. - you open the throttle. the TPS measures that instantly. very soon after the MAP (if there was one) will measure a reduction in vacuum, a little while later, the air will be moving faster past the MAF, a little later still the combustion by products will be breezing past the o2 sensor to be checked, but too late too do anything about it.
Just speculating - I don't claim to be an expert in this.
Quote from: shnazzle on May 16, 2018, 18:12
So I've packaged things up for you.
A veritable fun pack of analysis.
You will find
- 2 o2 sensors. Sorry, no long (cat) one in my arsenal. But process of elimination should make it unnecessary.
- one TPS
- one MAF
Start with the o2 sensors (their heater circuits are broken so expect codes), reset the ecu and try it out.
Then maf, as it's easy. Again, reset ecu.and try
Then tps
That's brilliant and thanks once again Shnazzle! I will go eliminating!
Quote from: jonbill on May 16, 2018, 20:23
That seems a reasonable plan of attack, although my money is on the TPS - I think it's the only thing the ECU has that enables it to see changes in demand instantly, and that's where the symptoms are. I think.
i.e. - you open the throttle. the TPS measures that instantly. very soon after the MAP (if there was one) will measure a reduction in vacuum, a little while later, the air will be moving faster past the MAF, a little later still the combustion by products will be breezing past the o2 sensor to be checked, but too late too do anything about it.
Just speculating - I don't claim to be an expert in this.
It'll be interesting to know what it turns out to be, but I'm not going to guess as I know little to nothing! ;D
The order was proposed based on ease of install more than likelihood to be honest :)
FYI the MAF is significantly more sensitive so it would sense changes before the map :) MAF is better, but a lot less flexible to changes in the intake tract. MAP is far more pliable but anything that changes the volumetric efficiency in any way and you need to remap the whole table.
Pros and cons as usual.
I suspect the tps as well tbh. The readings at idle and full throttle just don't add up
Kit posted
and now we wait :)
Quote from: shnazzle on May 17, 2018, 12:46
Kit posted
and now we wait :)
Indeed! I'm not here this weekend so the wait may be a little longer than expected, but I'll get on it the first opportunity I have! :)
Well, I've managed to fit the parts that Shnazzle has kindly sent through, but irritatingly, there is no change in the way it's driving.
So far then, I have changed;
- MAF
- Manifold O2 sensors
- TPS
Still the minor kangarooing, lack of power and struggling at half and full throttle remains.
Anyone got a match?
Have the fuel trims etc changed after fitting the parts shnazzle sent?
The figures actually look more normal.
I can see some key indicators that everything is responding as it should
- warming up. Revs slowly dropping and timing slowly dropping to 13.5-14.5. So your idle air control is working
- timing bottoms to 8 and low rpm high throttle (78%). As expected.
- max throttle value I saw in your recording is 80% and min at 12.5%. Minimum is spot on. Max is a tiny bit low but you may not have had foot to floor.
- you're missing some LTFT due to the reset. Fine.
Your short terms on the other hand show both massive under- and overfueling.
All your sensors are doing their jobs.
It's mechanical
I had a similar issue when I first bought my MR2. Slight hesitation when on full throttle, especially after changing gear. Cleaning the MAF made a small improvement but replacing the pcv cured the problem.
Quote from: shnazzle on May 22, 2018, 22:07
It's mechanical
Are we talking ancillary or darkest depths of the engine? :o
What's weirding me out is that it was (moderately) fine at the start of the day, then a simple plug and filter change and as if by magic, it's suddenly unhapppy. Much like its owner...
Quote from: The Arch Bishop on May 22, 2018, 22:37
Quote from: shnazzle on May 22, 2018, 22:07
It's mechanical
Are we talking ancillary or darkest depths of the engine? :o
What's weirding me out is that it was (moderately) fine at the start of the day, then a simple plug and filter change and as if by magic, it's suddenly unhapppy. Much like its owner...
Matt may be onto something with that pcv.
Cheap as chips via TCB.
PCV in terms of it being stuck open and letting increased air into the intake? OK - is it worth removing and cleaning out (more for speed than being a miser) before replacement?
Block it off as a test.
Undo the clip, pull the pcv pipe off and shove a spark plug or big bolt in the pipe. The pcv will just vent to air.
Reset and drive or drive for about 10-15 mins.
Right you are. Will give it a go! Thanks for sticking with it everyone!
Good and bad news...
This evening, I had a visit from a local MR2 hero Andrew, who came over to try and find out what on earth is going on with the car. First thing he did was to check the timing, so the rocker cover was removed to reveal a ridiculously clean and unworn engine. It looks like it may have had a recent rebuild or swap.
the timing was spot on, so no worries there. He put it back together and started it up and instantly decided from the sound of the engine that the plastic intake had started breaking up. After removing the throttle assembly, he managed to poke a camera inside to find that there was indeed plastic shrapnel in there.
Sooooo... obviously step one is to source an intake that isn't as brittle as Easter egg chocolate. Step two is deciding whether it is possible to replace the intake with the engine in situ. Andrew is prepared to give it a go, but thinks it may be a case of dropping the engine.... Larks ahoy!
Can I just say a huge thanks to all of you on here that have been so helpful and for putting up with my stupid questions! I owe you all a beer! :notworthy:
Wow. The failure rate is absolutely tiny and only increased in high power forced induction builds.
I don't suppose you know if the car has a history of having had a turbo?
Engine rebuild could be related
Doesn't look like it - I've got a lot of history with it and there's no evidence anywhere in that or with the car itself. It is bog-standard in every regard - just a pampered (for the vast majority of its life) car. But it's certainly had a new short engine and it hasn't done many miles on it either.
Andrew tells me it was a (low failure rate) recall for all of the other early applications of the 1zz but strangely not the MR2. Possibly because it was such an utter pain to do....
He's bringing an endoscope to double check but he's pretty confident.
Pics;
Fresh looking top end;
(https://farm1.staticflickr.com/890/42308155501_2664b9ee79_o.jpg)
And inside the intake (lot of oil in here as well);
(https://farm1.staticflickr.com/978/41406901665_361964c5f4_o.jpg)
The rings are the suspicious bits. orangey sealant used inside of them and a bit of plastic wedged in the runners. This is related by myself so it may not be entirely accurate but that's what I remember!
That oil don't look like oil :) From that pic it looks like your IACV coolant passage gasket went.
Hopefully it's all sorted soon. Getting the manifold out without removing engine might be interesting. Lots of universal joint connectors on tools :)
Fingers crossed mate that it's the manifold
Oh I certainly hope so! Got to love the Roadsters and their foibles! ;D
An update on this finally!
The manifold was swapped (it was not easy - I never want to do one again) and the whole thing's been put back together. The issue has not been resolved, but at least the car is working to some extent again!
Giving the car a fairly light throttle opening will make it cough before picking up.
So, today I've been faffing around with the MAF. I swapped my replacement out for my original one and it ran worse - occasional misfire at idle and coughed at any throttle opening. I took off the plug to the MAF and as if by magic, no stutter - throttle is sharp and responsive.
Put the replacement MAF back in and the cough was back but better than the old one. Again, unplugging the MAF solves the cough.
So is there any chance that I've been extremely unlucky and have two bad MAFs or does unplugging it and forcing it into a base map just get around an issue elsewhere?
Once again and again - any help/opinion/ideas are welcome!
I will flipping fix this car!!!
My recollection of unplugging the MAF is that the engine dies, but obvs not. I think the chance of two duff cheap MAFs is quite high. What value do they read at idle? Somewhere near 2?
There's always the possibility of a bad ecu
Quote from: jonbill on August 27, 2018, 18:37
My recollection of unplugging the MAF is that the engine dies, but obvs not. I think the chance of two duff cheap MAFs is quite high. What value do they read at idle? Somewhere near 2?
It does if you pull it while running, but if you restart and give it some throttle, it'll then idle and run. Not sure on the values - can certainly give it a look.
Quote from: shnazzle on August 27, 2018, 18:40
There's always the possibility of a bad ecu
I guess there is! The reason I'm obsessing about the MAF is because I was changing the air-filter just before the problem cropped up. Could just be coincidence though!
Anyone had the wiring or plug go bad?
Well I've gone through all of the things I can do without throwing new parts at it.
Checked for vacuum leaks at the MAF (found a new O-ring which seals it perfectly), checked the various other pipes that come off the throttle body/intake manifold - all fine. Sprayed some stuffy around to see if I could detect a stumble. Nothing.
Truly stumped!
I had another look at the trims - weird that the long term trims adjust seemingly on the fly from -8 on one bank -12 on the other at idle and then instantly changes to 0 and -4.6 at around 1500rpm. I'm not sure I'll ever really understand this thing! ::)
Air leaks should give positive fuel trims not negative.
I would replace the PCV valve first. If that doesn't sort it, try checking for leaking or sticky injector/s.
Agreed. Or, pull the pcv valve pipe off and block it with an old spark plug. Then you'll know as well.
Very easy test. It's just one little clip on the pcv valve holding the pipe on.
On the LTFT. You're not seeing rapid changes in fuel trims, you're seeing the different values in the table across rpm and load. On the Toyota these are very granular.
Quote from: shnazzle on September 2, 2018, 18:49
Agreed. Or, pull the pcv valve pipe off and block it with an old spark plug. Then you'll know as well.
Very easy test. It's just one little clip on the pcv valve holding the pipe on.
On the LTFT. You're not seeing rapid changes in fuel trims, you're seeing the different values in the table across rpm and load. On the Toyota these are very granular.
Quote from: lamcote on September 2, 2018, 18:42
Air leaks should give positive fuel trims not negative.
I would replace the PCV valve first. If that doesn't sort it, try checking for leaking or sticky injector/s.
I have previously checked the PCV valve and all seems well there. I also did do the test by blocking off the vacuum pipe but no improvement sadly.
I have ordered a new Denso MAF just so I can be sure that this is not the issue. Opie oils had a good price on therm and even if that doesn't sort it, I can be confident of that not cropping up in the near-future.
A sticky injector is a good idea for where to go next. It has history if this previously according to the history and looking at how Toyota replaced the dicky one (at the time - i removed the rail when removing the inlet), it's not the neatest solution. Basically, all bar the replaced one had a small black cap that fitted over the business end other than cylinder three which was replaced. Due to the missing cap on the replacement injector, they used a seal with a smaller internal diameter to fix the difference.
Thanks for the suggestions by the way. Internet diagnosis is about as far away from ideal as you can get, but it does at least give me a direction to go in so I am extremely appreciative of any help!
It's fixed..... :D :D :D :D :D :D
Anybody want to know what it was ?
Yes, I'm a tease....
Air leak :)
Nope!
It was indeed that I'd replaced a dead MAF with another dead MAF. New Denso one in there and it runs beautifully. Fuel trims have dropped to normal values, the stuttering has stopped entirely and the power has all come back.
I believe I've learned a very very important lesson here.
More than three months wasted by using second hand parts. Although to be fair, the part I used was working when it came off the old car (I trust the person I got it from). Just bad luck and terrible timing.
I'd also like to say a huge thanks to everyone who's helped me trying to sort this out with advice, lessons on how to read engine telemetry and spare parts to try out.
I feel a bit guilty for sort of wasting your time, but if it's any consolation, you've taught me a huge amount and been amazingly generous and I can't thank you enough!
(We need a group hug emoji one this forum)
Not a waste at all and I'm glad it's sorted.
I think, given the amount of knowledge on here now, it's time we step it up a notch.
If we had measured you maf signal, we may have known.
Quote from: shnazzle on September 7, 2018, 22:48
Not a waste at all and I'm glad it's sorted.
I think, given the amount of knowledge on here now, it's time we step it up a notch.
If we had measured you maf signal, we may have known.
To be fair, looking at comparisons, the ranges don't look radically different between the old and new MAFs. Which is odd!