Hey 6speeders

I've been battling a mostly unexplainable CEL (flashing and solid, intermittent) for months now.

Almost $10K and months later... it's still an issue. Both valve tappet solenoids replaced. Key Variocam components replaced (exhaust valve was sticking on Cyl 2), exhaust issue addressed, etc.

In addition, long story short, a bad experience with the local P dealer resulted in them "Accidentally" wiping out my tuned throttle mapping and resetting to stock. (I am shipping my ECU down to the original tuner to be reflashed, so I'll have it back shortly). That may be a factor as well.

In the meantime, if something here sounds familiar - your insight would be most appreciated. I am growing tired of the CEL saga, and so is my wallet...

This is CURRENTLY what is happening...

The engine itself runs strong, smooth and doesn't show any remotely-noticeable signs that anything is "askew". I've had multiple Indy mechanics do ridealongs with me to get their input as well. Everyone is saying it's running mint.

But it's still throwing codes. And the codes thrown range from bank-wide misfires (234 and/or 456) to bad 02 sensors to ABS(??), along with a few I don't remember.

It's all over the map, but the most common thing is the misfire codes.

The thing is - she ain't misfiring. The engine runs butter smooth. It simply is NOT missing, there's no way. (And yes, I've had all plugs/coils done - they're not even 2 months old).

So, the last few days I've purposely driven it a fair bit to see if I can notice any correlation between certain RPM's, speeds or otherwise conditions that "trigger" the CEL lamp.

Here is what I've found, and to me it makes no sense:

If I keep the car in gears 1 and 2, the CEL will not appear. I can lug it around, I can ride the variocam threshold (on/off at about 3K rpms), I can do max-boost 2nd gear pulls - you name it.

It's not gonna come on when the car's in gear 1 or 2, and for the most part, gear 3 as well.

But gears 3 and primarily 4 are the culprit gears, and I've now determined EXACTLY what triggers the lamp...

It happens in 3rd or 4th gear when I am sort of lugging along at just below freeway speed (so, 80 - 100 KM/hr), the RPM's are going to be around 3000 - 3400, which I believe is right around the VarioCam threshold.

Specifically - the light ONLY seems to come on if I'm using the throttle gently, AND if I let off the gas when coasting around the 3500 mark.

The bottom line is that I'm only getting a CEL when I'm driving very, very gingerly at low highway speeds when I let off the gas at 3.5Kish in 3rd or 4th.

Any ideas?

If I keep the revs high - no light.

If I'm driving like a banshee - no light.

If I'm in gears 1, 2, 5, or 6 - no light.

If I just let the thing idle in neutral and screw around with the throttle - no light.

Maybe I'm wrong, but when I'm just coasting along, gingerly using the throttle (and actually letting OFF the gas), isn't that the least likely set of conditions for producing a misfire?

You'd think it would be at max boost, under hard driving or otherwise NOT while "coasting".

Anyway, sorry about the novel.

I'm just going nuts trying to figure this damn thing out.

I know that it doesn't make much sense to try and diagnose until the ECU is properly tuned again, but remember that I was getting misfire codes even before the dumbass dealer "unflashed" my ECU.

Thanks guys...

Cheers

-Chris

 

What plugs are you running? I'm sure you have checked this out, but I had a similar issue in my 944 Turbo.. Turns out that I was running just ONE range too cold and at part throttle, my tune was just a bit rich, which slightly fouled the plugs and gave me issues. Same thing as you.. If I drove the snot out of it, I had zero issues.. The problem was worse in warmer weather when I was lugging around.. the air density made the car run even richer and fouled the plugs even more.. I went one range hotter on the plugs and the problem went away.

Not sure if that helps..

 

Part throttle light load and when backing off the gas sounds like a lean misfire. get it on a dyno and try to simulate the conditions and see what the afr is doing or throw a datalogger on and go for a cruise. Sounds like something minor maybe dirty injector or two?

As stated below if there is a vacuum leak anywhere from the MAF to the intake manifold it will create a lean misfire.

 

If you can get a Durametric, it is possible to record many functions including cams angle, number of ignition, etc etc... You just plug it in and select what ever you want to record and analyzed the numbers after your ride.... It is a very good tool for a case like yours....

 

I had very similar issues and they were all related to boost leaks on the intake side of the turbos. So under vacuum. It was part throttle or no throttle etc. I fixed these leaks and everything is fine now. Best way to check is to run durametric. Anyone with a tuned car should have this or something similar.

 

As most have said, most problems with these cars are boost leaks, vacuum leaks and MAF issues, o2 issues. That MAF sensor creates more CEL's and codes than you can imagine. Have you tried a new MAF and/or o2 sensors?

 

Hi guys

Thanks so much for all the help... much appreciated. (Sorry about the delayed response here, I've been head down, butt-up finishing my taxes all day... ugh.)

Sounds like the consensus here is boost leak/vacuum issues combined with 02/maf sensors.

And re: plugs, duly noted. What I will do is when I get a leak test done and likely the MAF sensor cleaned or replaced, I'll also swap out the plugs for some serious performance plugs.

I'll report back with my findings.

Thanks again, guys.

Cheers,

-Chris