gcpa968

I wonder if anyone has any ideas what might be wrong with my 1996 993 turbo. It runs fine when cool but as soon as it warms up and I try a full throttle run in 3rd it gets to about 5000 revs and then stutters really badly coupled with a kind of "baarp" noise (almost as if someone covered the air intake), lift of the throttle an inch and then floor again and it goes right through to 6000. I've had my mechanic look at this and he has run DME diagnostic checks on the car and has checked with the Bosch hammer, etc and everything seems fine, no misfire or any other problems listed. The car has a motorsport ecu (I didn't get the original when I bought the car) and he is going to try and slot in an original 993 tt ecu to see if that makes any difference. Kind of stuck at the moment and I'm afraid I have very little mechanical knowledge. Your thoughts would be gratefully received.

Thanks
G

Barney1

Check the fuel pressure..

ScottMellor

I'm sure someone more knowledgeable than I will chime in. You say you have a motorsports ecu: I wonder what boost it is running? It sounds as if timing is being pulled at 5000 rpms. A lot of people have experienced a 4500 rpm hiccup with non-stock ecus. Perhaps you are getting knocking when the engine is warm. Have you tried running a tank of 100 octane?

MarkD

I'd suspect fuel delivery first also.
The non-stock ECU second, though you didn't mention when the problem started. Is this a recent development?
Also, what do you consider "warm"? How many minutes of driving before things go wrong?

gcpa968

Thanks for the responses, please keep them coming. I had a replacement fuel pump fitted very recently and the problem only occured after this. This would fit with a fuel pressure issue perhaps but I would have thought this would be the first thing that was checked (particularly as my mechanic is pretty experienced with the 993s \ 993 tts). In terms of it being warm - it only occurs after about 5 - 10 mins of driving. A bit confused - as presumably if it was an ecu problem I would have experienced the stutter before now.

Thanks
G

911/Q45

Was the fuel filter changed as part of the pump change? Something could have broken loose and clogged it during the process or it is easy to kink a hose when reinstalling the pump.

gcpa968

Not sure whether the fuel filter was changed when the pump was. If the fuel filter \ fuel lines are prime suspect here I will give the mechanic a call tomorrow and get him to double check this area. Let me know your thoughts?

Thanks
G

Barney1

Thank you......
I felt I got trashed....

gcpa968

Would a fuel pressure \ delivery problem be consistent with a problem only at around the 5000 rpm mark which solves itself when you back off and then accelerates fine through to 6000 rpm ?

Thanks guys - input is appreciated.

G

Barney1

If you loose fuel pressure under a load at high RPM the car will fall on its face. I can't see how on the next full throttle it's then ok... You may also check the mass air meter. The element might be dirty and the computer is getting a false reading.If you use a air filter thats oiled you will have this problem. Wash the filter first and then make sure it's dry. CRC makes a mass air meter spray cleaner that works great.

911/Q45

A partial clog of the filter or lines could cause a loss of pressure under heavy load, then when you back off it could repressurize for the next go. MAF sensor is also a good guess, but that should show up on the codes check.

Felix

Do you have a separate boost gauge that you can verify correct boost levels with? Could also be a sticking wastegate but the timing of the problem with respect to the pump replacement does suggest they're related.

gcpa968

Thanks for the input. I don't have another boost guage. I have made a few suggestions to my mechanic. I read last night that the knock sensor kicks in \ pulls the timing at around the 5000 rpm mark which might fit with the symptoms. Fingers crossed I'll get the car sorted soon. What with the fuel pump problem and associated issues I have not been able to drive the car properly for a good few months now.

G

aperalta

I agree with what others have indicated. If you have your ECU remapped and have not addressed the fuel pump to keep up with increased HP, your starving the motor of fuel when it demands it most. From what I have read the fuel pump fix for more flow is not that expensive, couple of hundred $$ for 5 bar fuel reg. Others who have it may chime in here. Good luck!

911/Q45

The stock fuel pump has adequate flow for 550hp. The 5 bar regulator is a separate issue and should not be changed unless the ECU is specifically tuned for it.