joseph mitro

I’m at the track today and the car (86 951 engine) is stumbling at high load/rpm, almost like the car is running low on fuel (but it’s not). At half throttle it is bucking badly and around 4000 rpm the engine just cuts power like traction control is interfering. A cursory engine inspection indicates oil around the intercooler piping and AFM. I’m wondering if this is related? Could the engine be sucking in too much oil to run well? Is the AOS going bad (it has 2000 miles on it)?
or does it sound like fuel delivery problem? Fuel pump is original as is the fuel filter and injectors have not been cleaned

931guru

I recently helped a shop diagnose an 86 951 with a hard miss/backfiring problem under full boost in 3rd and 4th gear. We hooked up a remote fuel pressure gauge and found that it was half the pressure needed when the backfiring occurred. Shop replaced the fuel pump and the fuel filter, and the problem was fixed.

I'm not saying that this is your problem, but it could be... Good luck,

T&T Racing

Pull the spark plugs and see what is happening

joseph mitro

It is certainly possible the fuel filter, fuel pump, or FPR could be bad.

here are the spark plugs

joseph mitro

Plug gaps are in spec

edit - as I'm pulling things apart, I discovered one of the intercooler pipe hose clamps was loose (the clamp in the very bottom left in my second photo above).

this would probably account for the oil being blown around that area, and could have also caused the stumbling at high boost if charge air was leaking past the hose clamp?
thoughts?

931guru

Could be... tighten the clamp and see if it fixes the problem.

joseph mitro

welp; i think that's what it was. i tightened the clamp down, took it out for a hard drive, and no more stumbling under high load.
I changed the clutch out last weekend. I guess this was the only clamp I left loose

I'll still change the fuel filter and maybe the fuel pump as well

thanks for the replies

931guru

I nade a boost pressure tester just for the 944 turbo from an old fuel filter and an air hose connector. Fits in the J boot and can pressurize the entire intake system (I use 10 psi for testing, and a bottle of soapy water for suds). Excellent for finding loss of boost.

walfreyydo

Run a compression test. That's a lot of oil in your intake tract and to me suggests possible crank case pressurization due to ring blow by pushing oil into your intake tract via the AOS.

Compression test will tell you condition of your rings. If it passes then look at the turbo oil seals

Stumbling at high RPM definitely related to loose IC piping, but you may have other issues lurking.