Pesky intermittent start

[rmcdonnell]

Bother, my normally dead reliable 944 '89 2.7 is sometimes not starting. Usually it turns over 3-4 times then fires, but suddenly it's cranking away and not firing. Often, stopping the cranking and restarting a few seconds later will start normally.

Did it this evening, but was more persistent about not starting. I wiggled the DME relay, didn't start that try, but did the next. Once started, the car does not ever cut out. So next time it won't start normally what are the stages I should try?

Should I hear the fuel pump when cranking? I can't remember if I do or not. Should I make a jumper cable to replace the DME relay to prove that is my problem? This could also be the relay base I assume.

Anyway, a sensibly ordered checklist for now, and when it happens again, and any get out of trouble jumpers I might need would be useful.

cheers
Russell

[Icey1174]

The check valve on the fuel pump has proven to be the root cause of this problem for some people. Get a fuel pressure gauage on the fuel rail and measure the fuel pressure once you do get it running. It should be around 40 PSI. Let it sit for 20 minutes. The fuel pressure should read 20 PSI. After that it will eventually go to 0 PSI. If you are losing your fuel pressure at a quicker rate than that it maybe be that check valve or it maybe be a bad fuel pressure regulator. Get the fuel pressure gauage on and start there first.

You can make the 3 wire jumper relay for the DME. That would help rule out a bad DME relay.

The fuel pump only runs when the car is cranking or running. I cannot hear my fuel pump running while the car is cranking. The cranking makes too much noise. You could have someone else crack the car and put your ear by the back tire and the fuel door to see if you hear it running.

Some people have had problems with vac lines too. Could be a lot of things, but most recently people have been finding problems with that check valve in the fuel pump or the fuel pressure regulator.

Let us know what the fuel pressure gauge says and we can go from there.

[onZedge]

There is a procedure in the factory service manual for testing the fuel pressure regulator and check valve. Go here and download the factory service manuals (while you still can):

http://www.eucc.dk/manuals.htm

If the fuel pressure tests are OK, go to the next step. Find your wiring diagrams and use an ohmmeter to test your ignition switch contacts (there are separate starter and ignition contacts). They should be MUCH less than one ohm when the contact is closed. Intermittent problems can be a bi#ch to troubleshoot.

Report back.