Misfire on 996 turbo

[MIA 911]

Hi

Can anyone help me please? On my 2003 996 turbo I have a strange occurrence, if I accelerate hard in any gear when the revs reach between 5,000 and 5,500 rpm it holds back at these revs, it feels like you are hitting the rev limiter. If I keep my foot down it goes through it and revs round to 6,500 rpm with no trouble. The other odd thing is that if I turn the psm off it doesn't happen at all. Has anybody else had this problem? I have taken it into the Porsche specialist and they have connected it to their computer and no fault or error is shown, and they can't throw any light on the problem. One other thing does happen occasionally, the ABS and psm warning light comes on, but if I turn the ignition on and off again it resets and is fine. I have replaced the mass air flow sensor as I thought this may have been the problem, but obviously not. Thanks for any help.

Paul.

[blaineuk]

Sounds like a abs sensor fault.

[smj996c]

MAF sensor or cracked coil pack

[JNG1]

Duff spark plug?

[_gez_]

It does sound like a MAF problem. You got the same answers when you asked last year.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

[monthefish]

_gez_ said:

It does sound like a MAF problem. You got the same answers when you asked last year.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

...and how about now that he's changed the MAF sensor?

[MIA 911]

Hi
Thanks for your comments, but I have put a new mass air flow sensor on the car plus I didn't realise last time I put the post on that it was fine with the psm switched off. Thanks again.

Paul

[PHOENIXUK]

JNG1 said:

Duff spark plug?

+1

[MIA 911]

I had new spark plugs fitted 1000 miles ago

[matc]

MIA 911 said:

I had new spark plugs fitted 1000 miles ago

Could still be duff even though they're new. I spent a considerable amount of time and money some years ago trying to fix a missfire that occurred shortly after a service and it turned out to be a bloody spark plug!

[_gez_]

monthefish said:

_gez_ said:

It does sound like a MAF problem. You got the same answers when you asked last year.

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

...and how about now that he's changed the MAF sensor?

Oops, missed that. Apologies. As you fitted non-standard sized tyres you really need to rule that out as the cause (PSM incorrectly sensing wheelspin due to missmatch in rolling radius front to rear). Try and find some standard sized wheels/tyres to swap on for a test to rule it out.

[MIA 911]

The car worked fine for over a year with these tyres on. They are GT2 wheels and tyres which are 315 on the rear
and 235 on the front which I made a mistake and said I had 245 on the front which are a standard size for a GT2.
Thanks again.

Paul

[_gez_]

MIA 911 said:

The car worked fine for over a year with these tyres on. They are GT2 wheels and tyres which are 315 on the rear
and 235 on the front which I made a mistake and said I had 245 on the front which are a standard size for a GT2.
Thanks again.

Paul

And now the rears may have worn to a point beyond the PSM system tolerance. GT2's don't have PSM so that is irrelevant. I'm not saying this is definitely your problem but you need to rule it out before you start swapping expensive parts that having nothing wrong with them.

[Sunnysidebb]

Gez is correct about rear tyres, it can cause intermittent ABS/PSM failure with no codes. I have had this a few times when I changed my fronts but left the rears with about 2mm tread left.
Another cause for ABS/PSM failure is "Steering Angle Sensor" Failure ot out of tolerance. PWIS/PST2 and durametric will show a code for this. Not sure if the cheep hand held code readers will though.
Its easy to have the sensor re-calibrated and it should always be done after suspension work and geo set up.

[MIA 911]

Hi

Thanks for your comments about the tyres. I have only done approximately 3,000 miles since purchasing the car and the tyres still have loads of tread
on them. One other thing I didn't mention is that the car has been tuned. It puts out 587bhp. It had all been done professionally before I bought it. I don't know if anyone has got anymore thoughts.

Thanks very much.
Paul

[speedbird1000]

if it does not happen with psm off, it is very likely a tyre size mismatch (front back) triggering the psm. it could also be abs sensors. 587 bhp ? 3000 miles is plenty to eat the tyres

[Sunnysidebb]

Switching PSM on or off had no effect when I had the problem. The trouble is there are a number of non associated reasons "PSM/ABS Failure" can occur from Maf to Steering Sensors to actual PSM/ABS problems.
What annoys me about this is that even though there seems to be no hard fault when you get the light in the dash you have actually lost the PSM and ABS so you have got to stop, turn off the car and restart to get your PSM and ABS back.

[996ttalot]

MIA 911 said:

Hi

Thanks for your comments about the tyres. I have only done approximately 3,000 miles since purchasing the car and the tyres still have loads of tread
on them. One other thing I didn't mention is that the car has been tuned. It puts out 587bhp. It had all been done professionally before I bought it. I don't know if anyone has got anymore thoughts.

Thanks very much.
Paul

Has the indy actually datalogged to see if there are any misfires for example? I very much doubt that it is because it will generate pcodes unless the misfires are below 100.

Have you boost leak checked the car - this would give you the same issues that you speak of without given pcodes and is one of the most common causes.

As sunnyside said the sensor can also be faulty as well.

BTW, you can recycle the ignition whilst driving - just don't pull the key out - you don't need to stop. Just turn the key off and back on.

Could also be variocam related since that is when it goes into high lift. But again you would expect to see crank position sensor pcodes.

I take it you have hybrids fitted if you have "587hp"

Edited by 996ttalot on Wednesday 9th May 12:08