What a difference a MAF makes.....

Liz · February 21, 2007, 19:06

Thought that since I had changed the MAF and the car was running along nicely and pulling so much better that I would treat myself to a dyno run this afternoon..

This is pre-MAF change..

This is after..finally I break the 200 barrier, well 203.5 to be precise s:D s:D

I am well chuffed, nearly 10 HP difference, quite amazing really how much difference the MAF can make if it isn't working right! I have no more farting around and no more blip in the acceleration. The difference to Simons car was quite amazing too - his felt like it was running out of breath and is now cured.

kanujunkie · February 21, 2007, 19:09

now who's pleased as pie s:wink: :wink: s:wink:

excellent result Liz s:D

s:D

Anonymous · February 21, 2007, 19:10

everybodys going to be buying new mafs now s:lol: :lol: s:lol:

Liz · February 21, 2007, 19:12

Whats yours kicking out now Bossman?

andywood · February 21, 2007, 19:13

Hi Liz

I am surprised that a change to the MAF had such an effect.
Did you have any problem with the old one that made you change it?

The engine management system is normally able to detect a slight degradation in MAF performance as so much else is being monitored on the engine (i.e. HEGO sensors), and then will adapt accordingly.

Even dirt on the MAF thermistor is unlikely to cause a big enough impact to fool the engine in to running rich.

Don't want to spoil your fun, but could this be down to dyno variation - were both runs done at the same place on the same rig?

Anonymous · February 21, 2007, 19:14

i have no idea seeing as i dont have the car s:lol: :lol: s:lol:

still with SP but i will post the results, im interested to see how it drives compared to before!

aaronjb · February 21, 2007, 19:16

Quote from: "andywood"The engine management system is normally able to detect a slight degradation in MAF performance as so much else is being monitored on the engine (i.e. HEGO sensors), and then will adapt accordingly.

Considering at WOT the ECU isn't even looking at the O2 sensors as it's running open-loop, how would they compensate for a bad MAF? (For a start when turbocharged you're driving the O2 sensors so far out of range of their sensitivity band they're useless at any point other than cruise or idle when you're maintaining stoic)

I think the most telling thing, even discounting the power difference, is that there is no longer a big hole in the power band up top - it's unlikely that would be down to dyno differences IMHO.

kanujunkie · February 21, 2007, 19:22

hasn't Dan had the VXR on both of those dyno's?

andywood · February 21, 2007, 19:25

OK, so the HEGO example was a bad one considering it will be running open-loop,...
But, picking up on your point about the flat spot, surely you would expect a relatively uniform shift across the whole engine speed range with a problem MAF (taking into account engine speed and exponential output on MAF)?

Anonymous · February 21, 2007, 19:51

Quote from: "kanujunkie"hasn't Dan had the VXR on both of those dyno's?

Not on either of them mate, only at the one that me and Mark tagged along with the IMOC boys and girls.

kanujunkie · February 21, 2007, 20:10

Quote from: "andywood"OK, so the HEGO example was a bad one considering it will be running open-loop,...
But, picking up on your point about the flat spot, surely you would expect a relatively uniform shift across the whole engine speed range with a problem MAF (taking into account engine speed and exponential output on MAF)?

No, its a heated sensor remember, if the sensors created a point in the temp scale where it resistance changes drastically then the ECU will relate that to a certain point in the map and fuel accordingly, creating a flat spot

Quote from: "Ekona"
Quote from: "kanujunkie"hasn't Dan had the VXR on both of those dyno's?

Not on either of them mate, only at the one that me and Mark tagged along with the IMOC boys and girls.

could have sworn it was you s:roll: :roll: s:roll: , oh well

Liz · February 21, 2007, 20:12

Well can you explain then Andy, why my car and my husbands were running like that had both run out of breath and are that much better both running on new MAFs, hardly a co-incidence really. I have driven my car pre and post changing MAF - the difference is like night and day, no blip in acceleration and no running out of puff - pulls right to the redline now..when the bloke that done the dyno says how much better it was than last time says something really. Trust me - the MAF has made the difference between the 2 dyno's.

andywood · February 21, 2007, 20:28

Quote from: "Liz"Well can you explain then Andy, why my car and my husbands were running like that had both run out of breath and are that much better both running on new MAFs, hardly a co-incidence really. I have driven my car pre and post changing MAF - the difference is like night and day, no blip in acceleration and no running out of puff - pulls right to the redline now..when the bloke that done the dyno says how much better it was than last time says something really. Trust me - the MAF has made the difference between the 2 dyno's.

Currently just trying to eat my words! s:wink: :wink: s:wink:

Reason for my pessimistic approach to this one is that I spent a number of years working for DENSO with MAF sensors - I never saw anything like this in my time there, although the customer engines we were working on were large V8's and had much more complex EMS.

Doesn't matter what I say, you still got more power and a better running car for the Braintree bypass! s:D

s:D

andywood · February 21, 2007, 20:33

Quote from: "kanujunkie"
Quote from: "andywood"OK, so the HEGO example was a bad one considering it will be running open-loop,...
But, picking up on your point about the flat spot, surely you would expect a relatively uniform shift across the whole engine speed range with a problem MAF (taking into account engine speed and exponential output on MAF)?

No, its a heated sensor remember, if the sensors created a point in the temp scale where it resistance changes drastically then the ECU will relate that to a certain point in the map and fuel accordingly, creating a flat spot

Quote from: "Ekona"
Quote from: "kanujunkie"hasn't Dan had the VXR on both of those dyno's?

Not on either of them mate, only at the one that me and Mark tagged along with the IMOC boys and girls.

could have sworn it was you s:roll: :roll: s:roll: , oh well

OK, not trying to dig myself a complete hole here, but...

the maf has an external thermistor to measure air-in temp which should not be affecting this scenario at all.
In the MAF bypass duct there is the usual 'hot-wire' approach of arranging a heater element and thermistor in close proximity and wired in a wheatstone bridge styley. The electronics try to maintain a set heat transfer and therefore need to adjust when air-flow increases, thus determining mass air flow against a map programmed into the ems.
These elements are partial to build of general crap as particles will happily adhere to hot elements, but from my experience you would normally see a shift in output across the air-flow range.

I will make this my last comment on the subject as my shovel is starting to get worn out! s:wink: :wink: s:wink:

Anonymous · February 21, 2007, 20:53

This is a bit boring, but to sway any doubters.... when Liz first had the car dyno'd one of the suspects was the MAF. we swopped mafs, and though Liz didn't get any benefit my car started to throw CEL's, which showed it running lean - and a culprit for this could be the maf. Now my defective brain started to tick and suddenly, TOCK!, I bought a new maf, and WHAHEY! feels like a new car, whereas it used to struggle through a "wall" at 4500+ revs now it knows no bounds (see "spotted" thread). Now, my car had had a bit of a wall at 5000 revs before we swopped mafs, so perhaps my original wasn't that good to start with.. coincidence to each have a defunct maf but possible, so... Liz gets a new maf and the result is not just 10bhp,
it is s:D

s:D s:D

s:D

kanujunkie · February 21, 2007, 21:06

Quote from: "andywood"the maf has an external thermistor to measure air-in temp which should not be affecting this scenario at all.
In the MAF bypass duct there is the usual 'hot-wire' approach of arranging a heater element and thermistor in close proximity and wired in a wheatstone bridge styley. The electronics try to maintain a set heat transfer and therefore need to adjust when air-flow increases, thus determining mass air flow against a map programmed into the ems.
These elements are partial to build of general crap as particles will happily adhere to hot elements, but from my experience you would normally see a shift in output across the air-flow range.

yeah i know how they work, standard hot wire setup. But you can get a scenario where the resistance breaks down at a certain temp. I have to agree that i've never seen it on a car before, but then again thats not my speciality, its yours. But we do see it on the aircraft from time to time and its generally due to the extrememes of temperature that they get subjected to and have to correct for

Liz · February 22, 2007, 07:25

Just as a footnote to this thread - I have got a big thank you to say in public...and that is to the mods on here. There is a 10 page thread in the mods section dedicated to the problems that I have had with my car...they have all been a real huge support to me when I could of quite happily of parked it up somewhere and walked away.

Cheers guys - your the best! s:D

s:D

mr2mark · February 23, 2007, 20:12

Hi I have that "wall" at about 4800 rpm... Ive changed coil packs, injectors , spark plugs , even cleaned the MAF ..... After reading this subject I am definatly going to try a new MAF. ............ Then I mightbe able to overtake people again without having to pull back in all red faced s:oops: :oops: s:oops:

Liz · February 23, 2007, 22:02

Let us know how you get on with it won't you?

mr2mark · February 23, 2007, 22:54

Yes definatley.... I did try a maf off an mr2 I was putting a new engine into ... but it ran worse ..... But gonna try a fresh one ......... to be continued..........................

ChrisGB · February 23, 2007, 23:33

Can certainly vouch for it running well! Thanks Liz. (Un)fortunaltely I cant throw that kind of money at my '2. A properly nice to drive installation.

On the subject of MAF or any other sensor, it is sometimes seen that output is non linear or in error in part of the output range only. In the bridge, there is a varying amount of current being provided to heat the wire. It is easily possible that a termination somewhere in that heat balancing circuit is defective and at certain current / voltage levels changes resistance.

Chris

Anonymous · February 24, 2007, 06:24

Quote from: "Liz"Thought that since I had changed the MAF and the car was running along nicely and pulling so much better that I would treat myself to a dyno run this afternoon..

This is pre-MAF change..

This is after..finally I break the 200 barrier, well 203.5 to be precise s:D s:D

I am well chuffed, nearly 10 HP difference, quite amazing really how much difference the MAF can make if it isn't working right! I have no more farting around and no more blip in the acceleration. The difference to Simons car was quite amazing too - his felt like it was running out of breath and is now cured.

"I have no more farting around.."
by farting do you bean, a bang sound a bit like a backfire? My car does this all the time.. I'm pretty sure it's not normal, even tough I have TTE exhaust + gutted precats. When the engine is hot.. it's "horrible", it bangs allmoust everytime I drop the gas. it's not horrible, it's quite cool.. but sumthing shouldn't be good, I wonder what it is, but I don't have a clue where to start...

Anonymous · February 24, 2007, 06:26

Quote from: "mr2mark"Hi I have that "wall" at about 4800 rpm... Ive changed coil packs, injectors , spark plugs , even cleaned the MAF ..... After reading this subject I am definatly going to try a new MAF. ............ Then I mightbe able to overtake people again without having to pull back in all red faced s:oops: :oops: s:oops:

I don't have any walls so to say, and my car runs pretty fast. But at around 4000Rpm I can totally feel the diference in power (more power, like the engine has reached the rev range it likes to live on)

kanujunkie · February 24, 2007, 08:42

Quote from: "mr2mark"Hi I have that "wall" at about 4800 rpm... Ive changed coil packs, injectors , spark plugs , even cleaned the MAF ..... After reading this subject I am definatly going to try a new MAF. ............ Then I mightbe able to overtake people again without having to pull back in all red faced s:oops: :oops: s:oops:

could also be the VVTI

Liz · February 24, 2007, 08:43

Your talking about the normal noise like a "pop" that you get with gutted precats and a better than standard exhaust - quite normal and lots of fun. My turbo has just started to do it as well! Personally I like it.

My farting around referred to the car just feeling like she wasn't running properly and not pulling and being sluggish. Hope that helps.