Strange misfire or stuttering at higher rpm's at wot

[8757william]

I'm new to this forum, I've been reading posts off it for three months now. It has proved to be very helpful.

Three months ago I bought a 01 Turbo and ever since it has had this problem. At full throttle, in 3rd gear and up, once the revs get to 4500 or higher, it will have a sudden loss of power, the revs will climb very slowly it feels like a misfiring or stuttering, like its starving for fuel. Its fine in 1st and 2nd gear through the rev range. But 3rd and up once the revs get higher it happens. When it starts to stutter the boost will usually drop from .6 or .7 down to .4 and stay there. NO check engine light, no trouble lights at all. The car is all stock, No mods.

I have already done a boost leak pressure test up to 15psi, and its fine. I have installed new bosch fr6 plugs and updated 997 coil packs.

I have removed and visually inspected the MAF, I havent replaced it because from what ive read, when they're bad they turn on psm and abs lights.

I have a durametric, and this is what it told me (p1136 Fault code 440 pressure sensor signal comparison charge pressure/ambient pressure signal implausable). I cant find much info on these faults, Do you know what could cause them ???

Thanks for reading, please help if you think you can.

[Loren]

:welcome:

P1136 Pressure Comparison Charge Pressure - Ambient

Possible fault cause:

- Charge pressure sensor

- Ambient pressure sensor

- Wiring harness

[8757william]

:welcome:

P1136 Pressure Comparison Charge Pressure - Ambient

Possible fault cause:

- Charge pressure sensor

- Ambient pressure sensor

- Wiring harness

Thanks for the quick reply, I assume these sensors are mounted on the intake piping somewhere, one before and one after the turbos. Do you have any tips where I should look to help me find them.

[Loren]

Charge pressure sensor is in the intercooler (intake pressure side) pipe.

I think the ambient pressure sensor box is behind the dash/front console.

Have you looked for actual values reported for each of these on the Durametric?

Could narrow your search if one is zero or if charge pressure does not change with rpm.

[8757william]

The p1136 code I got from my durametric was from about a month ago, and I cleared the code after I wrote it down. Since then I changed the plugs and coil packs, and the car is still doing the exact same thing. So after Lorens sugestion today to get the actual values, I hooked up the durametric and it's now telling me missfires were detected on cylinders 4,5 and 6. (p0300,p0304,p0305,p0306) One time last week the check engine flashed 5 or six times quickly while the car felt like it was missfiring or stuttering, but it quit flashing and never came on since.

So I guess I might not have a pressure sensor problem, but what could be causing the missfire codes and this loss of power at WOT above 4500rpm??

[Loren]

Hmm... why only a pressure problem on one bank of the engine.

Only thing I can think of a bad hose or hose fitting.

[8757william]

Hmm... why only a pressure problem on one bank of the engine.

Only thing I can think of a bad hose or hose fitting.

I cleared the pressure sensor fault code a month ago when I first seen it. And today when I scanned it with the durametric the pressure sensor code was not there, only the missfire codes. Maybe the pressure sensor fault was old news, and had just never been erased. I did a boost pressure test already and it seemed to be fine, that would rule out most of the intake hoses right? Any other suggestions???

[8757william]

It missfired on cylinders 4,5 and 6, if they are all on the same side of the engine, would they all be controled by the same knock senor? Is there a chance I could have a faulty knock sensor or connection on that side??

[Loren]

I would go with what the fault code says - either there is a leak or the sensor is bad.

[8757william]

I would go with what the fault code says - either there is a leak or the sensor is bad.

Even though that code has not returned since I cleared it 1 month ago, you still think its possible it could be causing a problem?

[Loren]

Do you still get a stutter or misfire at higher RPMs?

If so then the problem is not solved. I would still check the hoses - you get almost no boost if you have a hose off/loose.

[8757william]

I cleaned the MAF with the instructions I found on here, but it made no difference. I used my durametric to watch the actual values for the charge pressure and boost pressure, and they moved up and down while I free reved it. And I watched the ambient pressure actual values and it was just a straight line, but I suppose thats what it is supposed to be?

I cleared the codes (missfires on 4,5,6) And I took it for a drive, everything is still the same, only at higher rpm (aprox 4500 and up) while accelerating it feels like the power is cutting out, and the rpm's increase very slowly. During idling or normal driving its fine. If I floor it in 6th gear at 60mph it will hold .7 bar and accelerate like it was new. The problem only happens at higher rpm.

After the test drive I checked for faults with the durametric but none have come back, it was only a 10 minute drive, but I did encourage the car to act up several times. I also watched the actual valuea for cylinders 1,2,3,4,5,6,misfires on the durametric while free reving it in the garage, no misfires.

Today I lowered the engine 2 inches with the instructions I found here and did another boost pressure test. I found a very very small slow leak coming from part no. 996.110.652.70 Venturi tube, it mounts right on top of the aluminum intake pipe beside the charge pressure sensor.

So I suppose I should order a new one of those? I have also been wondering about my DV's they are stock, but I cant recall ever hearing any honking sounds, so I dont know if upgrading these could help or not? Any other suggestions are appreciated, thanks for the help so far.

[8757william]

I think I found my problem..

When I tested it with the MAF unpluged, the abs/psm lights came on but it reved out in the higher gears without any hesitation or surging!

I did it atleast 4 times, hopefully I didint run it lean..

I was surprised to find it was the MAF, because I had no faults pointing to it and I never had the abs/psm lights come on before. It looked fine and I even tried cleaning it.

So I already ordered a new Bosch one off ebay $285 cdn shipped.

Thanks for all the help, I'll post back in a couple weeks after I get the part and try it.

__________________

[8757william]

Yes, it was the MAF, finally I can enjoy my car. Everything is working great, thanks for all the help.

[phillipj]

[OscarAH1W]

Thanks for the info on this... I just traded in my '01 C4 Cab for an '04 Turbo Cab with X50. Only had it a few days and gingerly winding it up here and there. Not used to this much power and PSDS only uses C2s so taking it easy here at first. Getting on the Freeway tonight, I got on it through 3rd into 4th and had what felt like the rev limiter kicking in; just a little higher RPM than you experienced. At first I figured i might have messed something up, but temps were up (never get above 3K RPM until 180+ degrees) and there were no lights. This car was babied, only 20K miles and owned by an older lady who only drove in town. How difficult was it for you to replace your MAF? I am not mechanically challenged (helicopter pilot) but not used to the lack of working space under the Porsche "hood". Thanks for any help you can provide

Cheers!

[jpflip]

Thanks for the info on this... I just traded in my '01 C4 Cab for an '04 Turbo Cab with X50. Only had it a few days and gingerly winding it up here and there. Not used to this much power and PSDS only uses C2s so taking it easy here at first. Getting on the Freeway tonight, I got on it through 3rd into 4th and had what felt like the rev limiter kicking in; just a little higher RPM than you experienced. At first I figured i might have messed something up, but temps were up (never get above 3K RPM until 180+ degrees) and there were no lights. This car was babied, only 20K miles and owned by an older lady who only drove in town. How difficult was it for you to replace your MAF? I am not mechanically challenged (helicopter pilot) but not used to the lack of working space under the Porsche "hood". Thanks for any help you can provide

Cheers!

Easy job, see MAF replacement DIY it is almost the same for the TT and also see MAF DIY. (Torx screwdriver needed) See picture for location and part# 996 606 124 00

info: a couple on Ebay....

Edited March 24, 2010 by jpflip

[Bostonduce]

owned by an older lady who only drove in town.

Was she little and from Pasadena???

Anyway...you need a T-20 security Torx bit (the one that has a center pin within its diameter). Remove the MAF first, then disconect the plug.

As a side note, be prepared that it's your plugs/coil packs causing the problem.

Use ONLY Bosch replacement plugs, not the factory Beru's, and if you do the coil packs, (you might as well since it's a b***h to do a plug change) change them to the upgraded 997TT parts. Don't let a dealer make the decision for you-they will more than likely use OEM parts.

BD

[greenboxster]

I had a similar symptom that was caused by failed coil packs, but it threw misfire codes. These cars can get pretty expensive if you just throw parts at the problem. You may want to scan the codes to see whether it is MAF or coil packs. Durametric pays for itself quickly!!

[SpecRacer]

Sorry to revive an old thread but I thought it may help someone with something that could be a simple fix.  I had a similar problem to the original poster, misfire on 4, 5 and 6 at WOT and running too rich.  I just wanted to add that cleaning my MAF fixed my issues which included a stutter in higher gears at high RPMs and a check engine light.  

Edited November 15, 2016 by SpecRacer