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joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

I have a 1983 944 that wont start unless you squirt fuel into the intake. Then she fires right up and runs fine and drives fine till shut off. Can this be anything besides the DME relay? I just put a used one on it like 3 days ago to get the car going, surely it has not gone bad that quick?

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

Sounds to me that its probably not the dme relay but the ignition switch/wiring from it to the dme relay. As a safety feature the car is wired to cut fuel supply under a certain RPM. By bypassing the fault (dumping fuel into the intake) you are in effect masking the fault.

Thats where I would look. If you jump the dme relay, does she run without dumping fuel into the intake?

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

this is where stuff gets crazy. I checked the DME with a good one and tried the one that was in the car in another running car. Both DMEs are good. I checked the voltage at the fuel pump fuse then the car cranked, it was on. I cracked the rail nut at the fuel rail and there was no fuel pressure. Hmm. I left the nut off and cranked the engine over and fuel shot out of the rail.

so.

Fuel is not building pressure but returning to the tank instead. I am guessing that I have a faulty fuel pressure regulator. Only problem is all my other porsches have the later style forward mounted regulator on the rail. So I cant swap parts to test it.

Here is the part that I am unsure about, I have no fire to my distributer now (I do have voltage to the coil) and the injectors have stopped firing. Why would my injectors suddenly quit firing and my ignition do dead?

I know that when the regulator fails closed and the fuel pressure at the rail rises too high the DME senses the increased draw on the injectors to open and shuts them all off. Does this happen when the fuel pressure drops to nearly nothing as well? Does the computer also somehow shut off fire to the distributer at the same time? Or do I have a failed coil as well?

jrrhdmust · Joined: 19 Mar 2008 Posts: 180 Location: Middle Georgia

I wonder if this is where the faulty ignition switch comes in.

I have been chasing Gremlins on mine for the last 4 months, with the car not starting in the morning, and then all of a sudden decide to start in the afternoon. I am going to run the wires and probably replace the ignition switch. I will check the speed and reference sensors as well as voltage to the coil and injectors.

I would like to see some more of the experts weigh in on this one. I am going to try starting with a prime also, to see if it works for mine.
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Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

If the coil isn't firing, the motronic isn't telling it to, or it isn't getting the message.

Assuming good DME relay, the suspects are crank sensor/wiring, or the motronic computer itself (board, connector, or wiring problem). I would swap a known good computer, then sensor.

Also, just for laughs, there is a known shielding issue with the crank sensor being interfered with by the starter, particularly on cars that have had the bellhousing cut to clear the sensor bracket.

Read and enjoy!
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joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

Pinned it down last night. Yes the fuel pressure reg was bad causing low fuel pressure and rail depressurization. However the injectors were working, but apparantly not clicking because there was minimal pressure on them. The ignition was due to a loose crank position sensor plug. It had no retainer clip on it and had just begun to wiggle apart. So with a squirt of gas in the intake she fired right up and ran. FPR arrived today so everything should be normal tonite when I put it on.

bcblase · Joined: 23 Oct 2007 Posts: 574 Location: Winchester, VA

An '83 944? That's almost a 924!
What are you doing messing with one of those?

Brad
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1987 Porsche 924S - track toy
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2007 F-150 5.4L Lariat Supercrew - tow beast
1994 Volvo 850 Race Wagon - 24 Hours of Lemons Car
2001 BMW 325xi - daily driver

joecitizennn · Joined: 12 Sep 2005 Posts: 2096 Location: no mans land

FPR on. she runs great now.

I used to not have much use for the generation 1 944 cars but they are really growing on me. I have over the last year or so decided that I like the old style dash much better. The later one seems generic and kind of blah. Plus on the older 944 you can remove the wheel spacer and run a shorter lug and super DEEEEp dish wheel. So far I have two 924S and two pre 85.5 944s and am going to pick up another tomorrow. That should keep me out of the house for the summer.