Mach 5

I traced a lack of fuel pressure after shut down to the FPR. I replaced it and now the fuel pressure holds after cranking, but the car won't start. Is there some procedure needed to purge air from the lines? I have searched all posts regarding FPR replacement, and all that is described is simply taking off the old one and installing the new one. The car started fine an hour ago with the old FPR, so I know it has something to do with the swap.

Any suggestions are welcomed.

Roger

Mach 5

Sorry, '86 951, if it matters.

Roger

SloMo228

When I replaced the FPR on my '87 S, it took a little while for the pump to repressurize the lines. I jumpered the DME socket to run the fuel pump with the engine off to prime the system first. Since it's a return-style fuel system, there shouldn't be any need to bleed air from the system, whatever may be in there will likely be pushed out by the fuel moving through. You could try tapping on the fuel rail while the pump is running to dislodge any stuck bubbles, though.

Edit: You may want to check your reference sensor connectors. I don't know exactly where they are on the 951, but on my 944S it's right by the FPR. When I replaced my FPR, I managed to break my reference sensor connector without even noticing. They're old and brittle and it doesn't take much force, just bumping it with my hand was enough to crack it. I ziptied it together as a stopgap until I could replace it with a new connector.

odonnell

Should be self bleeding, it will take a few extra seconds to get fuel after you install the new one but nothing obscene. Is the vacuum line plugged in? What pressure are you seeing?

Mach 5

The reference sensors are not the problem...this time. I just resolved that issue a couple weeks ago. Without getting into all the details, virtually every component that you could think of related to starting and running issues has been rebuilt/replaced over the last two years. Name it, it's been replaced!

With respect to fuel pressure, it is about 42 psi with the 3.0 bar and about 35 psi with the 2.5 bar, i.e., normal. The 3.0 bar was the one that doesn't hold pressure, so I swapped a "good" 2.5 back in.

Update: I swapped the 3.0 back in. Would not start at first but after some cranking, it did. Now I'll will swap the 2.5 back in. If it still refuses to start, I guess there must be something wrong with the 2.5.

Or...it is a completely new "random issue". Again, think "wack a mole".

Roger

Mach 5

Well, it's some random issue. It started, didn't run great with the 2.5 bar FPR, not like it did/should with the 3.0 bar. Brought it home. Let it sit. Won't start again. I dont know that this is the thread to get into all of this. I should probably just start another "944 turbo won't start" thread, outline everything that's been done, and start the process all over again.

Anybody wanna buy a 951???

Roger

Mach 5

OK, well I think I found the current problem...injector wiring harness. While its running, I can giggle the injector wires and get it to stumble and stall. I replaced the reference sensor harnesses a couple weeks ago because they were cracked and frayed. I should've just replaced the injector harness at the same time. I think I might replace the injectors as well. Hey, why not? Throw 'em in!

Roger