# Engine misfires only with MAF enabled



## Richtenb (Feb 1, 2010)

Hi guys i have a bit of a strange problem.

My cylinders are misfiring but only when i am running with my MAF enabled, If i run speed density with the same tune except that the MAF is disabled it runs perfectly fine. Not a single missfire on any rpm.

It misfires randomly aswell between the cylindars. I have tried with 3 different MAF:s and one is a brand new Delphi from GM and the engine mehaves the same with them all.

I have run the tune i got with my MAF enabled for perhaps 4 months without a problem and then suddenly it just started to misfire and blow my dipstick out. 

Car is running on brand new br7ef, same result with ngk tr6, brand new spark plug wires. Tune seems really good aswell when i am doing the logging, a bit lean on lower rpm:s and idle like i want it. The misfires starts directly on idle when i do the logging with hp tuners, on all rpm:s and it is heavy misfiring.

I am totally confused here about the problem, especially since the car is running great in speed density, narrowbands seems ok and the tune seems fine aswell. The maf:s i have tried are 2 Delphi from GM and one Summit Racing aftermarket MAF. The one i had in the car when the problem began was a delphi which had been fine for 4 months

Appreciate any suggestions, car is not throwing any codes unless i drive it for a while, then it throwes random misfires when running with the maf which wasn´t a big surprise....

Car is running on E85, Could it be the O2:s? even though i do not get any code?


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## Poncho Dan (Jun 30, 2009)

Misfires with MAF hey? What do your AFRs look like when it's happening? Could just be that the MAF got dirty... or it was never calibrated right.


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## Richtenb (Feb 1, 2010)

as it happens directly on engine startup at 800 rpm idle it´s about 15, slightly lean. actually it is at 9.92 or something if i translate to E85. I have tried leaning it out more, no difference. But the engine worked perfect with the MAF and without a single misfire on the same tune for 4 months, that makes me think that the maf is calibrated right.

I actually tried going back to the stock maf HZ aswell but same result


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## Poncho Dan (Jun 30, 2009)

That's a head scratcher. I guess try cleaning the MAF pickup sensor and see what happens. The problem lies in the MAF somewhere... sounds like maybe it's giving an erratic/jumpy signal.

Also, check the screen in front of it and make sure the vanes aren't kinked. If they are, you can use a toothpick to straighten them out a little.


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## Richtenb (Feb 1, 2010)

Yeah i Thought so to until: First i cleaned the stock sensor with brake clean and let it dry (always do that with my BMW:s and it always work) Nothing, So i tried my summit racing MAF with the same result. Then i went away to GM and bought a brand new OEM sensor, same result.... You could feel the whole car going really rough with all of the sensor and the strange thing was that it just started from one day to another. So 3 MAF sensors cannot be wrong or?

No changes in the tune or anything either


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## Poncho Dan (Jun 30, 2009)

When you log MAF hz, do any hiccups in signal show up on the "oscilloscope" plot? I mean, does the signal look lost at any point? It might be a broken/loose wire.


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## Richtenb (Feb 1, 2010)

Good suggestion.. Thanks Dan, have to check that up.. I get back with the result on friday or so when i have time to go and test it.


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## Richtenb (Feb 1, 2010)

Hi I tried logging the maf today on idle as the problem occurs directly on idle and on all rpms when driving. didn´t get any strange hz values on the MAF, i got pretty much the same that is entered in hp tuners. when i press the pedal it immediately writes values in the corresponding cells, doesn´t seem to be any hiccups. the HZ is rock steady aswell on idle, no difference at all if i let the throttle be. Non the less it is misfiring and running rough. I switched my front end narrowbands aswell to denso items, problem remained the same. 

I have followed the cable that is connected to the maf aswell but it looks good. 

when i did the maf log i logged dynamic airflow vs maf freq in hz of course

do you have any other suggestion on what to log?


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## Richtenb (Feb 1, 2010)

Here are my short logs with the maf enabled... i do not want do drive it for long with all thoose misfires. I renamed them to .doc and gto_procharged is the cfg file


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