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Rob001

996TT engine stutter under load

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My 996 turbo with 60K miles is stuttering under medium to full load starting from approx. 2800 RPM and also from time to time misfire noises from exhaust. Under slight load no stutter or not noticeable I got access to a PIWIS tester and no error codes at DME read out. In my opinion it is ignition related and I suspect the coil packs. Any other ideas or aeras to check? Could it be the MAF of O2 sensors?

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Tune-up ever been done? I replaced my MAF, O2s, coils, and plugs with new at 55,000 miles. Car drives much better now. I wasn't getting any codes (but I always wasnt experiencing back-fires). Good luck

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My 996 turbo with 60K miles is stuttering under medium to full load starting from approx. 2800 RPM and also from time to time misfire noises from exhaust. Under slight load no stutter or not noticeable I got access to a PIWIS tester and no error codes at DME read out. In my opinion it is ignition related and I suspect the coil packs. Any other ideas or aeras to check? Could it be the MAF of O2 sensors?

Are you sure your using a PIWIS or do you generically mean an OBD2 code reader???

A boost hose will show its self in no power, and a rather loud wooshing noise form under the engine. It will idle erratically and lambda will be trying to correct the fueling like a druggie looks for his next fix.?? You may even get an ABS/ PSM failure as maf goes out of tolerance. as asked are you actually using a Porsche System tester ( PIWIS).

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Yes I'm using a generic Porsche factory PIWIS tester, no Durametric or simular.

Narrowed down the symptom and it seems that only under boost pressure the stutter occurs and the boost pressure stays then low at 0.3 to 0.4 bar. As the stutter is not constant, when no stutter boost pressure goes up to 0.9 to 1 bar. Stuck or poor operating diverter valve issue?

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a "generic" PIWIS tester costs a bunch of $$$$$. (No such thing as generic...LOL). Still suspect a boost leak, waste gate problem or plugs/coilpacks.

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I know but with a lot of patience and the right equipment such as a Bosch KTS with a Porsche cable and IBM laptop I managed to get PIWIS V29 up and running... Re my stutter, booked for service today at specialist

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Are you sure the boost hose(s) are not collapsing under load? Old weak hoses will do that as well as not fit tightly at the connecting points.

What you describe still sounds like boost hose problems I have seen.

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How would you test that minus having car on dyno. Car shows misfires when problem occurs.. But no dtcs set changed plugs and coils due to service interval and coils cracked.

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The boost hoses consist of an inner and outer surface made of two different sort of rubber, by influence of residu oil, the inside can partially detached from the outer side. This can show two different kind of issues, partial blockage of air by the loose inside and loss of load along the more porous kind of rubber of the outside part of the hose. The hoses must be removed for inspection.

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As a follow up the stutter mysteriously cured by itself... kind off..

I suspect is was bad gas as the car was not used for a while as I'm often working overseas. I know that the ECU is flashed (unknown tune to me by previous owner) and I think the stutter was related to too much timing and the knock retard due to bad fuel. As a preventive measurement I changed the diverter valves (710N) and pre cat wide band O2 sensors. Next will be a new UMW tune based on a proper data log Kevin is selling.

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Replaced 996 coilpacks for 997 coilpacks and plugs, also had a leak on small hoses to diverter valves replaced valves with new billet DV and put clamps on all small hoses as they tend to pop off and changed out intercooler hoses to silicone, will some times go into limp mode with prior issues and boost leaks.

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Replaced Coil Packs, Plugs, both O2 sensors, MAF sensor, Air Filter, checked for leaks................

 

onto Diverters i guess!!!  Any Other thoughts guys??????

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Replaced Coil Packs, Plugs, both O2 sensors, MAF sensor, Air Filter, checked for leaks................

 

onto Diverters i guess!!!  Any Other thoughts guys??????

 

Did you check the car with a (Porsche specific) diagnostic tool for fault codes?

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yup no codes.... and now the oil pressure indicator is failing off and on.  This thing is either going to blow up or i have an electrical gremlin!!  anyone know if the oil pressure sender and the frequency valve are in the same harness???  would explain some things

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so many of us assume boost or electronic issues but fail to remember that engines need fuel.......... check your fuel pressure!!!!!!  blown hose on the fuel pump, and 20 psi pressure.......... 

post-101874-0-55656900-1432762000_thumb.

post-101874-0-22350500-1432762003_thumb.

Edited by taggs996
  • Upvote 1

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Hmmm...all three times my fuel line ruptured I couldn't get the car to start at all...so IMHO, your symptoms are atypical of fuel line rupture...

Edited by wross996TT

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Agree with Wross but found it interesting and also good to know!!!

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The split in the fuel line is exactly what happened with my garage queen X-50 a couple of months back and it took 7 weeks in the shop to reach that conclusion. Started with the obvious by having the dealer replace spark plugs, then it moved onto the fuel pressure regulator, checked fuel pressure (good), replaced fuel filter, drained and replaced the fuel, the two fuel tank pick-up lines replaced, inspected wastegates, all with no improvement. It fell on it's face under boost and massively stuttered, cutting out. But if you rolled into the throttle, keeping out of boost and not over .5 bar, it would pull evenly and smooth. No codes. After all that the mechanic suspected, perhaps, the MAF, so we consulted with Evoms since that is where the ECU tune was from along with their diverter valves and F pipe and they said the MAF failure is possible, but if replacing it we might as well go with the Hitachi conversion, intake kit, and their wastegates along with the corresponding ECU tune to get the most out of the car. Got all that installed and, unfortunately, no change. Finally, the mechanic decided to see if the fuel sump was staying full after a bit of acceleration by shutting the car off immediately while on an empty road near the shop and, sure enough, that was the issue. Took back to shop and pulled out the pickup lines/pump/etc... and the little U-shaped rubber hose at top had a 1 inch split in it. He replaced it and drove the car - it went like stink. Of course, with all the changes from Evoms we did he was over the top excited with how fast it had become, since it already pulled hard prior to this issue. Now it is an absolute beast and super fun to drive, spinning the tires in 3rd gear!

Anyhow, long story made even longer but just wanted to share in case someone else's car starts stuttering under boost. Don't immediately think spark plugs/coil packs...

Edited by kfitz911

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kfitz911 I'm surprised that you have check the fuel pressure and it was good even if the line was ruptured....It should be 3.3 bars + or - .2 bars ( 47.86 +or- 3 psi), is that what you got? 

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The split in the fuel line is exactly what happened with my garage queen X-50 a couple of months back and it took 7 weeks in the shop to reach that conclusion. checked fuel pressure (good), replaced fuel filter, drained and replaced the fuel, the two fuel tank pick-up lines replaced

Anyhow, long story made even longer but just wanted to share in case someone else's car starts stuttering under boost. Don't immediately think spark plugs/coil packs...

 

Yeah, I can't understand how they did a fuel pressure test and it passed with a split in that line.  With the splits I had, the pump just pumped fuel right back into the tank.  I'm glad you got it fixed, but I'm not convinced the split in the line was the original cause of your symptoms.  With all the trial and error done, they could have caused the split...so don't assume the split gave the initial symptoms...

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