Neverendz

I posted a few days ago about my crazy tach. Well, today I got into my 87 944na to go to work and- cranks, no start. Luckily I had my Portable Ignition System at home. This is a box that serves as a coil in case you have no spark. So I hook it up and get to work. On a guess I ordered a new coil, but to no avail. This is where it gets weird- I have fat, white spark from the coil wire! So, I pull the cap, clean, rotor, clean. The only thing I get is crank- run for one second- quit or ocassionally a sustained/rough idle at 400 rpm- but when depressing gas- no change! Weird! Could the DME be altering the spark advance wrong enough to cause a no start??? Nothing like owning a car for 4 days and getting a no start. Time to hit the books. . .

,Bill

Perry 951

It is a possibility that the DME has gone south, and using an ignition that bypasses it is temp fix.

Anyone have a DME he can borrow? I'd send you mine if you add a turbo and all the other goodies.

Neverendz

Yeah, but, err. . . DME = $Fat Qwon$ ! ! !

KW951

So this portable ignition works just like a coil? And the car runs fine with it in place? How does it know when to spark?

If you are getting spark from the ignition coil but the car won't run it does sound like the timing is off (since you know the cap, rotor, wires, and plugs are good). It could be a DME problem, or a problem with the timing sensors on the flywheel.

Perry 951

I would assume the special box has it's own pick-up. I saw one in a JC Whitney catalouge back in the day. You attach the magnetic pick-ups with some JB weld, and plug in the box if and when you need it.

If it is just a coil that gets the signal from the DME and it works, then you need a new coil.

Neverendz

The Portable Ignition System, or as I call it "The Hot Box" was made by KD tools. I bought it about 13 years ago. I don't know if they still make it, but I'll find out. You have a pos and neg lead to connect to the battery. There is an on-off switch and an ignition wire that you attach to the cap in place of the cars coil wire. When on, you have permanent spark. There is no spark advance, however, so driveability is poor. But it gets you where you need to go. These were great 5 to 10 years ago, but today everything is DIS.

The coil is new. So that's ruled out. Could be a stuck sensor on the bell housing causing full advance or retard. I was under the impression that one is for vehicle speed, and the other is for crank signal. I'll have to look that up.

What if I put the new coil in and that cured the problem? But since I was using the hot box the DME tried to compensate and is locked up in full retard? Interesting. I'll have to disconnect the battery and then see.

I'm hoping it's not the DME. I've never done any repair to one, and an exchange is still fat.


,Bill

PeteL

Have you tried swapping the DME relay? Cranking with no start is a symptom of failed relay. About a 25 dollar part.

Neverendz

Okay. Last time I posted I was down to either bad speed sensor, bad ground/wiring/connection or DME. I checked all grounds that are ignition related- OK. I checked continuity of wires from, coil, speed sensors- OK. I pulled out both the reference sensor and the speed sensor. I did a sweep test and they both produced a signal, but sometimes these sensors can appear to be okay and aren't. So, I then swapped them just for kicks, still no start.

As logic dictates; if the car has injector pulse the reference sensor and speed sensor have to be working. I have injector pulse, but no spark. The DME works spark and fuel separatley. All arrows point to the DME. The only way to test the DME is to supply a known good.

So I went over to the closest Porsche dealer and described my problem and finds to a few of the techs. Everyone agreed on the DME. One of the techs had two spare DME's, but of course wouldn't lend it to me because he doesn't know me. So he said to drive the car over on the hot box and we'll plug one in. I did so. Car starts. Since he had one to many DME's sitting in his box I offered hime $200 for it. Good deal in my opinion.

Thanks everyone for the help.

,Bill

Water944t

OK, maybe I can help a bit...

I had a very similar problem, turned out to be worn and brittle wiring on the injectors. The wires were coming into contact under the rubber boots, and shorting/fscking the system. It was causing the exact same symptoms you are describing, crank but no start. Spark and fuel appeared normal, compression was good. When I finally rewired the injectors, no more problems.


Hope that helps.


edit//

I just saw that you fixed it with a DME swap. Oh well, remember this one, it might help another time.