odonnell

The car cold starts just fine, but when heat soaked (up to temp, left to sit for 5+ mins) it starts but then instantly dies. It sounds like classic fuel pressure to me but am unsure about how the pressure should look during a hot start. It's annoying because I just replaced the FPR and pump less than 4 months ago.

I hooked up the gauge and here's what it does when it stalls: during cranking it's ~2.6 bar and it fires for a few revolutions before it dies. During that time it doesn't discernibly go below 2.5 bar. After stalling the gauge is back at about 2.6 bar.

So how high does the pressure need to be to overwhelm the driver and send it into self-preservation mode? It's my understanding that if the injectors draw too much current (i.e. high pressure) it shuts itself down to prevent damage.

I have tried starting the car on 3 cylinders (one injector unplugged) with no success. Maybe the injector driver in the DME is damaged?

When idling, the pressure is 2.1 bar and is 2.6 bar with the vac line unplugged. When revved it drops down to 1.6/1.7 bar which makes me think this new FPR may already be bad. Car is running noticeably rich.

marc abrams

Mike, I never heard of a "self-preservation mode" on any car? I can't see how high fuel pressure would cause high amp draw. You mentioned it starts fine when cold and run's rich, I would be looking at the coolant temp sensor and idle speed motor.

odonnell

Post #12 in this thread is why I still think this is the problem:

https://rennlist.com/forums/924-931-...ce-needed.html

I installed a new FPR just now and it hot starts just fine, so maybe that was the problem and I just had a defective part. Although it still dips down to ~1.6 bar of fuel pressure when I rev the engine. The coolant temp sensor is about a year old, I'll measure it just for good measure though.

As for the idle valve, the early cars have a simple bypass that gradually closes as the engine heats up (not a motor). If I keep my foot on the gas a little it still does the same thing so I ruled that out. Someone correct me if I'm off on that one though. When it is finally running, it idles great and I can tell the valve is smoothly opening.

Tiger03447

Dear Michael: I can understand a slight dip in the fuel pressure upon revving, due to pressure lag in the rail, however, when revving for say, over 30 seconds, if the pressure doesn't come back up, I'd suspect a clogged fuel filter (or two) or perhaps a failing pump or a kinked fuel line..or one with a partial blockage..Have you changed out any of the fuel lines recently, or never?

odonnell

Fuel filter and pump are both less than 6 months old. As for fuel lines, the ones under the hood are < 10 years old and the ones near the tank are about the same. The hardlines near the torsion carrier were crimped about a year ago so I cut out the damaged section and replaced them with rubber hose sections designed for fuel injection.

marc abrams

Mike, you have the same car car as mine. I was thinking it was a turbo from the avatar.

Your pressure seems ok for for starting. Does the pressure drop in that 5 mins the car is off? I'm thinking leaky injectors and loading up?

odonnell

Not a hair. I have over 2 bar for 1hr+ after shutdown. Everything rebuilt.

konakat

I had a similar issue that also manifested as stalling when the car was running more than 45 minutes or so. I suspected fuel pressure but it ultimately turned out to be a bad DME.

marc abrams

Mike, did you ohm out the coolant temp sensor yet and if you did, was it done at the DME so to check the entire circuit? When it stalls does it start up and die or nothing, will it stay running if you hold the throttle open?

odonnell

Yes, and it was right on point. I measured it at different temps from both the engine bay, and from the DME connector with a few ohms difference but 99.9% the same reading.

Go figure I went to start it and it fired up, but died after ~10 secs. All signs point to a bad electrical connection.

Swapped in the old AFM and early DME... fired right up, idled perfect. Drove it around and did errands to charge the battery and started fine every time I restarted it. Guess it was a flaky DME.

marc abrams

Ok, good to here Mike!!

odonnell

I don't believe it... Back to the same antics. Starts but then loses power even with giving it throttle. I'm thinking it has to be ref sensors at this point, literally everything else has been tested or replaced.

marc abrams

Mike, if you think its the ref/speed sensors, forget that tach bounce crap, use a noid light to rule out the sensors, DME. If the fuel end checks out ok, maybe start looking at the ignition. Don't assume its new its good.