weird starting problem

I have a 84 911 with an intermiten starting problem. Occationally, usually when the engin is warm, the engine will crank normally and strongly but not start. It either is not getting a spark or not getting fuel. After a while it will start right up. One dealer said it might be a DME relay that often fails on older DME cars. Any ideas out there, should i just replace the DME relay and see what happens?

Hi. I too had an 84 that did the same thing.It sounds like the check valve in the fuel pump is bad. If the car always starts normally when cold, but is only difficult to start after its been driven and then sat for 15-45 minutes then that is what it is. what is happening is the check valve is not maintaining pressure in the fuel line and you have to crank the car awhile for fuel to refill the lines with pressure and start injecting. because the engine isnt really cold the engine management doesnt revert to a cold start situation (rich)like it does in the mornings or after it has sat for a long period.

You can check this by clamping the rubber fuel line on the engine and waiting about 20-25 minutes. after that remove the clamp and try to start the car. if it starts you have a faulty check valve. On Carrera I believe you have to replace the whole fuel pump because the check valve is part of the whole thing.good luck

Michael

You can test that relay after removing and cleaning the connections with a stainless steel toothbrush and isopropyl alcohol! All that is required is a pair of jumpers with clips on each end, and a multimeter -- analog or digital makes no difference!

To Test Relay off the vehicle:

1. Apply 12-15 Volts DC to terminals 85 and 86

2. You should be able to measure less than 1 Ohm resistance between terminals 87 and 30

3. Apply 12 to 15 Volts DC to terminals 85B and 87

4. You should be able to measure less than 1 Ohm resistance between terminals 30 and 87B

As much trouble as people have had with that relay, I would recommend getting one and carrying it in the glovebox or trunk as a spare, regardless of your test results this time!

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Warren Hall
1973 911S Targa

my 74 2.7 cis did the same thing, and the problem was that the mixture was lean....adjust it and the problem was fixed.