87924GT

Hey,
I'm coming home to the land of the watercoolers. My last Porsche was an '86 Carrera slant that I built last year and I really appreciate and now remember how well balanced the 944 platform is. I just bought an '86 951 (my 1st turbo)thats's been taken care of by a friend of mine that works in a local independent Porsche shop. When I bought the car I was told that the TPS was the problem, but it's not. TPS was replaced and still it won't pull past 4200, under boost and not act like the fuel shutoff is kicking in. Could it be a vac leak or what? I cleaned the TB when I changed out the TPS because is was just a little dirty. It wasn't nasty, just dirty. I'm new to the turbo side and do all the work on my cars at another local Porsche shop.
Any and all suggestions will be appreciated and thanks in advance,
Steve Ed
Stratton MotorSports

Ski

for sure check all the vac lines, and double check the ones to the FPR and dampner - this 4200, it's under full boost? If the hoses on the intercooler and especially the TB hose are old, these can have splits that only reveal themselves under boost.

Is the car stock or what mods?

Mighty Shilling

Also, just a thought, considering I've never experienced a knock sensor...

But, maybe you're running a little lean, and triggering the knock sensors into making it slow down?

bearone

was the tps changed to a new one or one that was thought to be ok?

87951

ibkevin

A bad knock sensor will pull 6deg of timimg.

87924GT

I checked the hoses Sat and they looked and felt OK. I'll check those again and also the FPR and dampner. The car's been chipped (Welt) and has a boost enhanser. I noticed a little oil from the intercooler tube on the left side facing the engine. It wasn't more than what I'd call residue. Is that normal?
TPS is Bosch new.
I'll 1st check for vac leaks and then the knock sensor.
Steve Ed

Epic2112

You could also swap out the AFM, if you have a known good one that you can try out. That *might* be the issue as well.

Daniel Dudley

AFMs do cause stumbling at precise rpms, as the flap rubs the variable resistor in a worn spot, usually the spot where it stays during cruise rpms. Dirty pin connections can also cause this.

I don't know 951s. Is there an overboost cutout switch ? How is your fuel pressure ?

dand86951

Does it have an adjustable fuel pressure regulator? If so it may be set for too much fuel or conversley too little fuel pressure. What boost level is the boost enhancer set at and what boost are you seeing when it stumbles?