Engine holding back at wide open throttle

[The Arch Bishop]

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.

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.

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.

[Smcknighty]

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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[The Arch Bishop]

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....

[shnazzle]

Vacuum leak. Pcv hose? Evap hose?

[The Arch Bishop]

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.

[lamcote]

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.

[The Arch Bishop]

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
I admit this is all unknown territory for me!

[lamcote]

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?

[shnazzle]

Not convinced your o2 sensors are kosher. Particularly bank2. (left)

[lamcote]

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?

[The Arch Bishop]

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

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.

[shnazzle]

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

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.

[The Arch Bishop]

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

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!

[shnazzle]

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

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

[The Arch Bishop]

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!

[shnazzle]

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)


-

[The Arch Bishop]

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?

[shnazzle]

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.

[The Arch Bishop]

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! 

[shnazzle]

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! 

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

[The Arch Bishop]

That's ridiculously good of you and I'd be very grateful. I'll send you a PM.

[shnazzle]

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

[jonbill]

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.

[The Arch Bishop]

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!

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! 

[shnazzle]

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