944 Turbo no start (sometimes)

carolinatrophy · 05-14-2006, 02:20 PM

I hope someone can help me diagnose an occasional no-start problem with my 1986 944 Turbo. The symptoms are almost exactly like a failing DME relay, but I have changed the DME relay several times and the problem persists. The details are as follows:

1) Whenever the car has been sitting for any appreciable length of time (enough to substantially cool down) it starts perfectly. No problems.

2) 95% of the time, even when it's hot, it starts perfectly.

3) VERY OCCASIONALLY when it's hot, it will fail to start. Cranks perfectly, all the electricals seem to work fine, but it just won't start. Just like a bad DME relay, but again, that's not the problem.

4) Generally, I can just wait five minutes or so and try again and the car will start. A few times, I have just sat there cranking it for five or ten seconds at a time, and after a few minutes of doing this, it eventually caught and fired. But sometimes it takes a bit longer.

5) If it's not starting and I sit there cranking it anyway, when it eventually starts it starts perfectly. It doesn't cough or sputter or anything. One minute it won't catch and then the next minute it does.

Again, if the car has been sitting and is cold, it ALWAYS starts right up. ALWAYS.

Any ideas of what I should check?

Thanks in advance,

nynor · 05-15-2006, 03:09 PM

check grounds at the fuel pump, etc. also, could be the pump itself. or the check valve... or the fuel is vapor locking as it sits there, getting hot in the fuel line.

carolinatrophy · 05-15-2006, 04:46 PM

Will do, thanks!

Lawrence Coppari · 05-16-2006, 08:54 AM

Also check the connections were the crank position and rpm sensor unions are. They are in center about 8 inches from firewall. They come from clutch housing near the top. I had this problem a number of years ago. Engine would always start cold but occasionally not want to start when hot.

Next time yours does that, unplug each one and replug it. That could be the problem - dirty connectors. Don't mix them up.

carolinatrophy · 05-16-2006, 09:04 AM

Thank you! Are these the two connectors (that look identical to each other) sort of at the top of the bell housing? Like, you look down past the oil fill cap and you see them down there, next to each other, each held on by a 10mm nut? With rectangual plastic connectors?

They look like they might be a beotch to get to... Are those the ones?

Lawrence Coppari · 05-16-2006, 11:07 AM

They are connected by a nut but I'm talking about the union about 8 inches from the nut. The union is where they plug into the line that leads to computer. Will post picture in a few minutes.

Lawrence Coppari · 05-16-2006, 11:12 AM

Lawrence Coppari · 05-16-2006, 11:16 AM

Picture shows one of them circled faintly in red. It is in vicinity of O2 sensor connection. There are two of them. Do not unscrew from the clutch housing as their postion is fairly critical. Too deep and flywheel mills them off. Too shallow and no signal.

ae1969 · 05-16-2006, 11:27 AM

Do a simple test.........

WHen you get the no start occuring.... carry an extra plug....

Pull one of the wires and attach it and lay it on the manifold. Fire it up. If you have no spark. You can rule out the fuel pump and vapor lock.

The connectors that lawrence mentioned are definitely a big problem........... if you ever have the pleasure of cutting into ANY of the connectors on a 20 year old 944 you will find the leads extremely corroded. They normally look fine from the outside....

carolinatrophy · 05-16-2006, 11:35 AM

I just went out and found one of them, now looking for the second... But I'll get it, and thanks so much for the picture - I wouldn't have found them without it!

carolinatrophy · 05-16-2006, 11:36 AM

PS - I might be interested in your 450SL. Can you send me details and photos and your asking price? My direct email is paul at carolinatrophy dot com. Thanks!

carolinatrophy · 05-16-2006, 11:39 AM

<< WHen you get the no start occuring.... carry an extra plug.... Pull one of the wires and attach it and lay it on the manifold. Fire it up. If you have no spark. You can rule out the fuel pump and vapor lock.>>

Yeah, good point. I'm almost positive it's fuel, because if I keep cranking and cranking, when it fires, it fires right up and idles cleanly immediately. If it were spark, I would think it would sort of flood while it was cranking, and then eventually fire and run crummy for a bit before it cleared itself out...

Lawrence Coppari · 05-17-2006, 06:42 AM

Will email you pictures later today along with description.

ae1969 · 05-17-2006, 10:07 PM

Quote:

Originally posted by carolinatrophy
<< WHen you get the no start occuring.... carry an extra plug.... Pull one of the wires and attach it and lay it on the manifold. Fire it up. If you have no spark. You can rule out the fuel pump and vapor lock.>>

Yeah, good point. I'm almost positive it's fuel, because if I keep cranking and cranking, when it fires, it fires right up and idles cleanly immediately. If it were spark, I would think it would sort of flood while it was cranking, and then eventually fire and run crummy for a bit before it cleared itself out...

The point of the exercise is to determine the following....

If you have spark and no start then yes.... possibly fuel.

If you have no spark and no fuel. Bad reference sensors, connections, dme relay, dme etc..

The last possibility of no spark with fuel usually leads me to check the rotor, coil (rare).