RC713

Background: So I had an intermittent no start situation on an 86 n/a I picked up a couple of months ago. I changed out the reference sensor because it was a rig job, cut on both sides with bus connectors from Radio Shack making the connection. While I was at it I replaced the harness back to the DME as well. I started up the car just now and it died after running for a couple of minutes (always warm my cars and bikes up) and wouldn't start back up. I checked the connections, even pulled apart the wiring harness connection into the DME to see if a wire had come loose, it hadn't. I tried it a number of times and...

The clue...the "!" light that is always on (it is alerting me to the brake fluid light being on even though the fluid is fine) wasn't on and no tach bounce. Then I would try again and the light would be on and it would start and run and then die. Try to start it again and it correlated perfectly, no "!" no start and no tach bounce, if I started cranking (it always cranks) and the light was on from the turn of the key it would start (and die). What's this telling me?

Thanks all in advance.

944Ross

I would guess it's the ignition switch, not putting power to all the circuits. Before cranking, the "!" light should be on because you have no oil pressure, if nothing else, and since it isn't, I'd suspect the circuit isn't being powered up.

dv8nxs944

I'm not sure but mine was doing the same thing and ended up being the DME relay.

cb944

the cutting out and not starting does sound exactly like the DME relay, mine did that when I was driving it, not fun... but the '!' light not coming back on and no tach bounce... I don't remember that - but I would definitely switch out the DME relay with a new one anyway, just to rule it out. They're not expensive - or if you're good with a soldering iron, try resoldering the contacts. I've still got my old broken one here, bizarrely I found it today and was looking at it about an hour ago! It looks fine inside the casing, so I suspect they suffer from poor solder joints.

Chris.

RC713

Tried the DME relay from my parts car last night (I think it's good), tried the one from my 951 today (I know it's good) as well as the actual DME itself from my parts car, (tested it in Spencer's car so I know it's good) got the same symptoms, no lights, no start. Plugged back in the old DME and relay and of course, dash "!" light came on, fired right up. Sat in it and the "!" light was flickering AND (new info, hadn't noticed) the gauge showing the alternators output was bouncing off the bottom, usually I get at least 12 even at idle, was off of that a good amount. It then died, tried to start it again, no light, no tach bounce no start, but it does crank strong. So...if it was the alternator it should still run the ignition off of the battery, correct? It would set off all of the dash lights and run poorly as it drained the battery but it should still run, or are these cars different?

dv8nxs944

The tabs on the inside of mine weren't making contact so I was told to wedge a piece of cardboard in the contacts and try it and it worked.

RC713

Even after testing the DME itself and a couple of relays, say it was that, would a bad DME or relay cause a no tach bounce situation?

cb944

I don't know the answer to that, because I don't remember what happend with the tach when mine failed, but just a thought.. my understanding is that a bad DME relay stops the fuel pump from working. Get someone else to crank the car and check if you can hear the fuel pump whirring.

If it's running, then it's not the DME. If it isn't, well, then you still have no clue other than it might be the DME

RC713

Any ideas fellas? My non-running car has my running parked in, kind of stuck... Thanks for any ideas, my next thing to check is the ignition switch, looks like a PITA, please feel free to stop me if the symptoms don't reflect that as a possible problem. Any other suggestions?

V2Rocket

IIRC your ignition switch was pretty soft, may be time to replace. I had a similar problem a few months ago

RC713

O.K. So I thought I had this cornered, that it was the ignition switch, the part forward of the tumbler. That's where the actual work takes place to charge the electrical system and run the car, correct? The tumbler just either releases to allow the philips head in the ignition switch to turn or not correct? If I am wrong please let me know, I changed out the ignition switch (link to the picture of said part below) for the one from my parts car (always interesting to have the neighbors come by when you are upside down with your head under the dash and your feet over the top of your headrest...I'm 6'1 220lbs, must have looked pretty comical). No luck. I have been toying with the idea of a pushbutton start, and while watching a video embedded in a how to post by Campeck I noticed something, that when he switched "on" the system (it is a two part switch, power up, then a push button fires the starter motor), basically I think the equivalent of turning the key to the "run" or "on" position, all the gauges came on, alternator, fuel, etc. Mine stayed dead, I checked in my 951, turned the key to the run position, dash gauges came on. New (different) ignition switch, same exact symptoms. What else might cause this? Please feel free to take any stabs at this, I am out of ideas at this point. Sorry for the long post, just wanted to give as much detail as possible. Also included the Campeck post so you can see what I mean (and a pretty cool design if I do say so).
http://944online.com/images/products...ignswitch2.gif
https://rennlist.com/forums/924-931-...e-a-944-a.html

RC713

Just made some jumpers, pulled the alarm control module, jumped it per Clarks instructions, that wasn't it, checked the connections on the coil checked the set screw on the rotor, pulled a plug, no spark... Any ideas? Cleaning the grounds is next I guess. Cranks and cranks and cranks...

Grandpa#3

Hi RC713, If you have NO 1/16" Tac Needle Bounce try wiggling the connections at back of engine or have someone else do it while you try to start. I still think you have a bad Ignition Switch Module. Did you put in a NEW one to test it out? I would have loved to have seen a Gent your size crammed into the foot well. I had the same No Start as you are having, same systems. I'm 70 and can't get down like that anymore so I had to take out the gages. Fixed the No Start and brightened up the gage lights while in there. I hope you figure out your problem.

Cheers,
Larry

till_that_day

I'll preempt this with saying that the above posters seem to have much more electrical knowledge on the Porsche than me....

I know its not that great for the systems, but have you tried a shot of starting fluid. Its an instant tell of weather or not you have spark.

I'll just say I've had coils crap out on me in other cars and do the same type of things.

RC713: did you check incoming voltage to the coil?

specsalot

The DME harness had eaten my lunch a few times so far. Tach bounce proves speed sensor and a good portion of electronics / ignition system. Fuel spray out of injectors proves DME relay, fuel pump, reference sensor, and CPU. I've found lots of issues with wiring in DME harness on harness side of plugs.

Lately I've had an intermittant stall at idle, with an immediate start up. This could be created on queue by wiggling the reference sensor wiring on the DME harness side plug. Cut back the boot to find (no surprise) bad insulation - shorting wires. Taped up - problem temporarily solved. 20 Year Fix - rebuild DME harness.