+1, for a quick check. place your DME into a known good car. NO WORRIES your DME will not harm the donor 3.2.

+1 Check the OHMs on the CHTS, Ref & Speed Sensors

+1 check fuel pressure, HB has a cheap but effective test kit for $20

Thank you for all of the most recent replies (and the earlier ones). I will start with these in a few weeks--I am on a lengthy business trip to Central Asia tomorrow...

Jonathan

Measure the fuel pressure and see how quickly it drops when shutting the engine off.
It should maintain pressure for 20 minutes or so, if it drops quickly you know there is your problem. Could be the fuel injectors or the pressure check valve.

HI Jonathan, got your PM - not sure I could add much to what the guys have said. Safe travels and let us know how it goes when you return - sry you're having an aggravating time with this bit of 'fun'.

Can you describe what its like when the power cuts out? Does it feel "digital" or "analog"? Ie does it feel like you're loosing power like sucking thru a straw with a hole in it, or that something electrical is causing more of an on/off stumbling?

Have you checked your distributor recently?

How old is your battery? I have found that when batteries get old they get "weird". Had a problem like that on a motorcycle once - it cranked and started with great ease so I never suspected a battery was the cause of the problem, but at strange times it would cut out much like you describe and I got several no-starts that seemed unrelated to anything. I believe I did check it with a volt meter but can't recall if that diagnosed it or if I just upped and replaced it. I would almost certainly replace yours or at least swap it with a known good. I have an optima and it cranks like its angry, all the way down to sub zero.

Past that I would try to purge your mind of possible causes and just look at your motor, top side, bottom side, just look for cracks, smoke, loose bits, corroded grounds, eyeball it for things that shouldn't be.

Folks, I finally solved this. My winter maintenance included the following:

New O2 sensor
New speed sensor
New cylinder temperature head sensor
New TDC reference sensor
New bracket for the speed and ref sensors
New DME relay

After the first four, car was definitely running better. After the DME change (my old one was like a box of Good'N'Plenty at a movie theatre--it literally rattled when I shook it) it runs beautifully and idles steadily at an indicated 880 rpm. I am happy I changed all the sensors as the old ones (especially the last three sensors) all were showing many signs of age--flaking rubber on wires, discolored heads at the plug end. Changing them was tedious, but not difficult.

Other items completed over the winter:

New heater hoses from heat exchangers to main heating system
Brad Penn 20 W 50 oil change, new filter, new drain plugs
New J tube from the oil tank to the engine oil cooler (old tube was feeling weak...)
Bilstein sport shocks all around
New Hawk HPS brake pads--I read these generate a lot of dust; let us see
Rennline pedal set and dead pedal--accelerator pedal is fully adjustable
Rennline driver and passenger floor boards and track mats

Now all I have to do is put in my Das Sport rollbar--which I am about to repaint--and I will be ready for the DE at Watkins Glen in June.

Jonathan

Well done.

Can someone describe what the DME Relay is doing? I am only familiar with relays for switching ie headlight relays. What is it that the relay does for the DME brain?

Thanks r-mm. I did as you suggested last autumn and spent quite a bit of time just gazing at the motor and hoses/connections to see if anything looked odd and might indicate a vacuum or other problem. Did not find anything and it seems to have been sensor/DME related in the end.

I am also curious to hear what the DME relay does for the Motronic box; I know it also serves as the relay for the fuel pump.

Congrats!

I experienced the same issues starting the car after a long run but never when it was cold. What I did was to check the voltage at the fuel pump fuse (after the dme) in the morning or when cold (before starting, fuse removed). Then checked it again after shutting it down after a long run (again with fuse removed). The voltage reading dropped. I replace the dme relay, now I can actually here the pump kick in. My problem solved!

Which one solved your problem/s?
 

Jonathan,

Good to hear the good news and the car is running satisfactorily. However, you did not mention which remedy did actually fixed the problem. You replaced a lot of parts which are not cheap for some people and sharing your findings would be much appreciated by others. Thanks.

Tony

http://forums.pelicanparts.com/porsche-911-technical-forum/849856-getting-know-our-911s-performing-some-basic-tests-before-there-problem.html#post8468264

1987 911 Cab starts and runs great after a cold start but dies after a few miles, but starts right back up and runs fine until the next cool down. Then repeats the above. Replaced everything except computer.
Any suggestions, I'm desparate!

^^^ As Sal suggested, check the DME computer for solder cracks, especially where the coil transistor sits up off the board on the aluminum heat sink. Very common failure with similar symptoms to yours Boots.

Chuck.H
'89 TurboLookTarga, 429k miles

Can you get hold of another 84-89 DME from a buddy? I suggest trying another 84-89 DME in your car. If you need help testing your DME PM me I may be able to help.

When it fails to start, do you have spark? Test for spark during failure.

I thought that if you remove the oil cap you should notice a change in the engine - idle drop an/or rougher idle. Thats what happens on my Carrera. I had a vacuum hose leak years ago and the tell-tale sign was no change in RPM or idle when the oil cap was removed. Removing the cap creates a vacuum leak, so if there is no change when cap removed, doesn't that mean there is already a leak somewhere else? In my case, a couple of new vacuum hoses fixed the problem. The hoses may look fine, but still have cracks that are not easily visible.

I doubt your stall/restart issue is caused by a vacuum leak. Even if you possibly have a leak that would not likely cause a engine stall with no restart.