924Board.org

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

I recently bought an '87 924s, and the car is in great shape.....minus the fact it won't start.
I have replaced the ignition coil, battery, rotor, distributor cap, and spark plugs, and it still won't start. It sounds like the engine really wants to turn over, and I get a fast "re-re-re-re-re-re" sound every time I try to start it. I get 1 spark when I try to turn it over (found out using an induction spark plug tester), then nothing more.
I've done some research and the only things possibly remaining are the DME being faulty or the crank sensor. If anyone has any ideas or has had this problem, I'm out of ideas and things to try and would love a fresh perspective. Hopefully someone knows how to fix this!
Help me please!

edredas · Joined: 09 Dec 2004 Posts: 861 Location: Charlotte, NC

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

I don't think that's the problem because I'm not getting a spark. The timing belt rotates and seems fine. Thanks though

headstrong2740 · Joined: 29 Apr 2010 Posts: 111 Location: Moline IL

so your getting a fast re re re re re and only one spark... and then thats it?

Are you getting any pop or slight chugs or anything? Smell Fuel from your exhaust? Did not notice anything in there about fuel and could be a factor as well... but sounds more like spark is your main problem so....

I would look into the timing as mentioned.. or i would look at your ref. sensors then

I know the DME relay controls the fuel pump... but dont think it controls spark.. I think thats more your cam/crank sensor.

As far as the DME itself being bad... i would go as far as to say its doubtful. Not impossible... but doubtful... try to see if you can get a few new ref. sensors or even used ones from a parts car or somthing and try that route.

Hope you figure it out
_________________
1987 924s "Enzo"
2002 1.8t VW Passat
http://porsche924resto.shutterfly.com/ - follow the progress of "Enzo"

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

Definitely check your sensor(s). I think you also have an ignition control module (in addition to the DME?)
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

headstrong2740 · Joined: 29 Apr 2010 Posts: 111 Location: Moline IL

i dont think there is a control module on the 924s .... atleast i have yet to see one

the 944s and s2 did but not sure baout the 924s
_________________
1987 924s "Enzo"
2002 1.8t VW Passat
http://porsche924resto.shutterfly.com/ - follow the progress of "Enzo"

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

I was under the impression that you only needed the reference sensors to keep the engine running. I thought that during starting a 12V signal overides the sensors. I'm going to check several signals with an oscilloscope tomorrow including those sensors. Any other advice/thoughts of what to check?

headstrong2740 · Joined: 29 Apr 2010 Posts: 111 Location: Moline IL

no actually those sensors are used to tell computer when to fire the spark based of number of teeth count

But could be wrong... just my understanding of it
_________________
1987 924s "Enzo"
2002 1.8t VW Passat
http://porsche924resto.shutterfly.com/ - follow the progress of "Enzo"

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

I read a bit that the ignition control module function was moved in and out of the ECU. Here is an excerpt I found on Rennlist.

"I think all 944s have them. But on the 8-valve cars, and the 968, they're in the ECU.

I think that the all-too-common 8-valve ECU failure is in this stage of the ignition. And since it's part of the PCB in the ECU, you have to buy a whole new ECU. I thing Bosch either discovered this problem after the 944 had been out for a couple years, or suspected it might happen, so at the time of the 16-valve engine management re-design (knock sensors and stuff integrated), they decided to move it out of the ECU and to just about the furthest point from the ECU they could find.

Then after a few more years, Bosch solved whatever the issue was with putting the igniter module back in the ECU, and put it back. So the 968 has the igniter module back inside the computer.

I'm not sure what it actually does, though. It does "something" to the signal from the ECU to the coil.

Bryan"
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

If the crank reference sensor is non-op, the car will not start.

The other thing I learned the hard way when I had a 924S is that (on my car anyway) it was very sensitive to loose connections at the battery. Make absolutely certain that BOTH battery cables are tightly connected to the battery posts, that you have a good clean ground, and that none of the leads coming from the positive cable are loose or frayed.

On my car, a problem similar to what you described turned out to be nothing more than a loose battery cable that I had forgotten to re-tighten after replacing the starter. The car would crank and crank and crank, but wouldn't fire. Retightened it, and voila! It's a long shot, but worth checking.
_________________
erstwhile owner of just about every 924 variant ever made

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

I checked the ref. sensors and the speed sensors with an oscilloscope and they seem to be perfectly fine. Also, I was getting the starter solenoid signal, but the was no pulse most of the time and if there was it was only at the very beginning

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

On our older cars we have a pulse picked up from the ignition coil, that is used by the fuel pump relay as a signal that it is OK to run the fuel pump.

If you car works similarly, and you have no pulse or just one at the beginning, and you similarly describe just having a possible spark just at first, I'd look at the ignition module, or DME if the ignition module function is embedded within.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

Went back and checked again, and I found that the speed sensor is supposed to make a saw-like wave, but instead I was receiving a sine-like wave on the oscilloscope. After checking resistances under the hood with a voltmeter on the sensor itself (was testing on the connector near the DME) I found the ref. sensor is normal but the speed sensor seems faulty

edredas · Joined: 09 Dec 2004 Posts: 861 Location: Charlotte, NC

CabooseSA · Joined: 14 Jul 2011 Posts: 18 Location: Virginia

I checked the resistance on the speed sensor and got infinite for both. I suspect the sine wave signal present on the speed sensor was not actually being generated by it. I have been trying to remove the speed sensor but it is really stuck. I have sprayed on some grime cleaning agent but it hasn't really budged. Does anyone know a removal procedure? Or if it is different for an automatic transmission?