Hi all,

I have been having an issue, which at first seemed fairly obvious, but now is a little odd. I am experiencing some misfires under load and wide open throttle on boost in second and third gear. Originally diagnosed as plugs, but after the second set (problem went away each time), it is apparent that something else is happening.

This is where it gets interesting. I reset the ECU and the problem has gone away, and the car runs better than ever (for now).

Is the ECU trying to adjust to misinformation resulting in the misfire after time? Is there a sensor that could cause this if faulty?

Has anyone experienced something like this?

Cheers,

 

Need a little more specifics...what kind of plugs on first and second set? mods completed? Time or mileage gap between incidents? When did you reset the ECU/after changing plugs a third time or after immediately after the second set, or on the second set but just after the incident came up again? What type or types of fuel? Geographic location? I assume this is recent so all summertime heat and humidity are in effect. No codes apparently either, MAF or MAFless? Sorry but you could really get down a rat hole pretty fast without isolating some variables.

 

Original plugs with 15k, then IR22 and back to new factory plugs. Only a couple of of thousand miles from the first incident until now. Reset the ECU today after the third set started to play up. Drove about 20 miles with misfiring, then drove a 100 miles with no problems after the reset. The only mods are Softronic, GMG racing exhaust, AP headers and BMC filters. It is the start of winter here in Australia, but still fairly warm (10-19 degrees Celsius). I only run 98 RON fuel, which is equivalent to 93 in the US.

 

First, I think the IK-22 is too cold of a plug for those mods not allowing the plug to ever reach its cleaning temp so that it can burn off deposits. How did they look once you removed them? The short time period does seem to question if the the ecu was compensating for the fouling plugs, but I believe the root problem is the plug and not the ecu. SOFTRONIC could probably give a little more intelligent feedback than myself on this part. I run the IK-20 with no issue and expect to get 30k out of them. There is a post on 14 JUN labeled Spark Plugs for flashed car....where is explain the plug ratings. What made you go with IK-22 instead of 20s? Did a shop or someone recommend them. This is the second car with softronic flash and similar mods that fouled out the 22 plugs early. Cheers...

 

Check your coils
Check the headers could be cracked
Check FPR
Check if there is a leak ( start with I/C hoses and between the Y-Pipe and TB )

 

What fuel are you using?

 

FPR reference line? https://www.6speedonline.com/forums/...ml#post2971110
Other possible leaks
Check coils for cracks in housing
Cat converter clogged

 

I am just spitballing so please don't get offended.
A pressure leak down in any stretch of the system would seem to cause a misfire but would not reseal itself and remain constant after ecu reset or play change. As long as you test on WOT in the same gear range and similar terrain so as to create the same demand on the engine. The headers being cracked would be a similar failure as well and the ap headers would have to take a significant hammering to crack. The FPR is a good one since you were giving it the juice at failure, but I would think that a bad coil would throw a code. I have had pressure leaks that threw a code, but not 100 percent on the FPR or coils giving a code. If no durametric then you would at least see the check engine light. I am here to learn as well as help so I am just trying to talk this out.

 

Damn you auto correct. That should read after plug change instead of play.

 

afaik, cracked coils, loose fpr line won't throw a direct code. AP headers and other aftermarket ones have been known to crack at the welds in the past so definitely check there. Stock are very solid.

 

Dave, what do you think about dirty MAF sensors?

Dirty MAF sensor = incorrect airflow readings = lean condition?

I'm trying to think simple problems that could cause this - his setup is pretty basic.

 

Good point Bob. I agree, check the "easy" stuff first. I saw an 07 997 CS2 come in the shop with misfires in bank 1. His cat had "melted" for some reason which backed up the exhaust flow. The cat was replaced and that solved the problem. Might as well check the turbo actuators too. There was a service advisory on those a few years back.

 

Is there any test for a dirty MAF or you just pull and spray them both?

 

There's a PIWIS test for malfunctioning maf which would throw a code. Turn ignition key to on position and voltage should be under 1.1 volts. If over 1.1 then bad maf sensor. Turbos could spew out some oil vapors which may slowly collect on the maf over time. Check by visual inspection.

 

Thanks for all the good feedback guys.

The exhaust is new (post first and second plug failure), I can't see any cracks. I rechecked the second plugs, they were ik20, no visible damage. The problem followed the plug when the coils were switchEd at the time of the second problem.

Would the problem go away after the reset if it was the fpr?
The maf sounds possible, doesn't the computer run a mafless program immediately after reset.
If the problem starts to return today I will let you know.