Battery cable came loose when driving

[mhariush]

and then the car died. And doesn't want to fire. It cranks, but doesn't fire.

1987 S.

I haven't done all the tests yet, will do tomorrow but I tried replacing the DME computer, DME relay and Final Stage ICU unit, still no start. And there's no bounce on the tach.

What could have happened when the negative terminal came loose? Could I have frayed something?

[9FF]

Alternator diodes are normally the first thing to blow, but without a ground on you car voltage spikes and surges might have caused other damage. The battery not only supplies voltage it also grounds everything to 0v, something that sensitive electronics is very sensitive to.

Check alternator output at battery then systematically check fuel and ignition system.

[mhariush]

I swapped the alternator with one from another car, as the old alternator was making a loud whine noise. Still no start.

[944tothefloor]

If the cable just came lose, are you sure you're having good contact with all the wires on the positive side of the battery? A little rust and looseness caused the problem you described on my car. then i cleaned everything up, tightened it down, and the problem was solved.

[mytrplseven]

You should check the Ref Sensors with an ohm meter and see if they read around 1000 ohms. Check ClarksGarage for the info on which pins to read.

[mhariush]

the neg came loose beacause i prob didnt tighten it enough and i acutally cleaned both terminals with a wire brush a few says ago. the positive is now nice and copper colored. and theyre both tight again.

[mhariush]

Checked the resistance on the Speed/Ref Sensor, got the correct ohm readout.

Tried with a different ignition coil, still no start. I tried checking for spark with a spark tester, its hard to do by myself but looks like I wasn't getting spark. And no tach bounce.

[mhariush]

Getting 11.5 V on the pos and neg coil side to ground.

[mhariush]

changed ignition switch and bypassed alarm. Still no start.

[djnolan]

Fuel pump or DME relay?

[mhariush]

fuel pump is brand new and I've tried a new DME relay.

[thekidd]

need 12.0V or greater to start the car. Try jumping the battery, all the starting attempts may have drained the battery. If it doesnt charge back up, get a new battery.

[mhariush]

Battery is good. The non start began after the negative lead slid off while driving. It wouldn't fire after that.

[djnolan]

is there spark when cranking? Are the plugs wet from fuel or smell of fuel after a good cranking? Can you try a spare known good dme? Put the dme from the dead car in one of your other running cars and see what happens?

[John_AZ]

Fried the motronic DME computer.

and do not jump the car even if is mentioned in the owners manual.





J_AZ

[944 Ecology]

On a 944S, you may have got lucky and fried only the output stage for the spark. It is located on the inner fender of the driver side, below the headlight. If you have a spare (you should), you might try that first.

[mhariush]

Don't see any spark.

I've tried two spare DME computers and one other Ignition Control Unit aka Final Stage (the one on the fender)

Still nothing. I'll try a second Ignition Control unit today and a third spare computer.

I had similar issues once and had to take it in to a shop and all they did was change the ICU/Final Stage

I also bypassed the alarm by jumpering it as per Clark's

[djnolan]

you can buy a sparkplug tester to verify spark if you are working solo.

[mhariush]

I tried with a spark tester, didn't see any.

But I started going through the DME test plan, and on Test point 3 b I found a problem

I am not getting voltage between 24 and 37 with the ignition on. I tried this on the other S I have and I got power. But I did not get power on either when trying the 14 pin plug. And I have working DME relays (tried 2 spare ones)



But what exactly do they mean by "check power supply from ignition lock via the alarm unit to terminal 86 of the DME relay to the wiring diagram"?

[mhariush]

I made a new thread to try and steer the troubleshoot in the right direction

DME Test plan help - 944S non start