1987Porsche944WithRealLongName

Had an issue with the alternator wire rubbing on the exhaust and it caused some problems including killing my DME/eprom

Now that I've got that sorted the car runs... If you can get it started. I put the key in and turn it to accessory and everything lights up, turn it further and the engine won't attempt to turn but my gauges will wobble, the oil pressure gauge will shoot up to 5 bar and the tach needle might go up and down. No fuses were ever burnt. If I do get it running it will act normally for a few minutes before starting to run very rough and dying.

The ignition switch tested fine as per clarks
Same story with the starter itself
I removed the starter to alternator cable and tested with a multimeter to make sure none of the wires inside it were rubbing
Battery has a full charge of course

It is a somewhat intermittent issue, the car will start just long enough to get me stranded. Everything seems to be checking out fine, where should I look next?

kniners

Sounds like you have a short to me.
- Make sure the insulation on the wires to the starter is fine.

Happened to me once. A wire was grounding. (in the work truck '86 944)

1987Porsche944WithRealLongName

I figured as much. I tested the #30 plug to battery and #50 to the starter solenoid and both wires were fine.

Could the ignition switch still be bad even though it tests fine and all the lights come on? Do the ignition relays have anything to do with the starter?

1987Porsche944WithRealLongName

Alright I'm lost, I don't know where to start.

The starter and wires going to the starter are all fine
The ignition switch is fine

I tried getting it to start just to see and it fired up. It ran decently for a few minutes and then suddenly started getting rough. I looked at the gauges and noticed the tach was sitting around 1500rpm but I don't really think it was that high. The wideband gauge was showing things go from very rich to very lean, eventually I went ahead and turned it off. I immediately tried to start again and it went back to clicking and pegging the oil pressure gauge.

Where should I start looking for the short? I can't make sense of the wiring diagrams via pdf.
None of the fuses have blown but I tested the ones without fuses in them for shorts and found that fuse 17 (central locking) is shorting out.

kniners

Just pissing in the wind here, maybe replacement DME?

It ran fine before Alt. wire issue?

944hal

You need to tackle one problem at a time. There is a big plug on the firewall, engine side, near the fuse box. The wire from the ignition switch to the starter solenoid runs through there. Mine car had a problem with this wire. So, two things to try. Put a meter on the positive cable, or power cable at the starter and see if you have 12V. Second, run a 10 GA wire from the solenoid up near the positive battery terminal. With the car in neutral touch the wire to the positive side of the battery. If the solenoid closes and the starter cranks, you have a bad wire from the ignition switch to the solenoid.

1987Porsche944WithRealLongName

I believe the problems are related as the car ran fine before the alternator cable shorted out. I have already confirmed that the starter works and the engine turns over fine when bridging the 12v source from the battery to the solenoid.

I followed the shorting fuse lead to pin 87 on the G2 relay. It's grounded here too.
One question I have is how does power enter the inside of the car? Do the 3 red battery wires go through a switch or are they wired right into the fuses?

thomasmryan

Meters really don't tell the whole story sometimes. Have you tried a temporary DME relay bypass?

If you get it running, wiggle the key and see if that causes a disruption.

If the alt wire shorted, the insulation on any wire in its current path and or relay, should be investigated. From your description, the pull down/control coil in the dme relay maybe weak and loose contact after it warms up a tad.

Tiger03447

Dear PWRLName: You say that it clicks..that to me indicates that the battery voltage is low or perhaps has a bad cell...Have you checked the cells with a hydrometer to see if there is a bad one??did you rewire the alternator to the battery? I presume it was the main alternator discharge wire to the battery...Is there any green showing in the battery cables (corrosion)? this will add resistance to the charge going to the starter...since the alternator was shorted, sounds like you need to remove the alternator, and take it down to AutoZone for a free test on their test bench...Take the battery too for a good checkout...and recharge if necessary that's free too BTW. You might take the starter too for an amperage check on the test bench while it's doing a free spin...They can print off the numbers for you to see after each test is complete...If all these check out,and the problem persists, it's either the switch or the wiring...that's about all I can suggest for openers...Thanks, Tiger 03447 Keep us posted on what develops..

1987Porsche944WithRealLongName

The battery is new, I got it back when the issue first started creeping up. I replaced the alternator with a spare I had at the time and it does charge.

All I can figure is that when whatever wires short out they draw such a large load from the battery that none is left for the starter. Is this likely?

1987Porsche944WithRealLongName

Something else interesting:

With the key not turned the positive battery cable to ground reads 0 ohms
With it turned to accessory it reads 15 ohms
With it turned 'on' it reads 3 or so
If I push it back towards on after doing that it'll read 50

So this confirms a short somewhere behind the ignition switch, right?
My DME harness doesn't seem bad (I haven't pulled off the big rubber hose part yet though)

1987Porsche944WithRealLongName

I seem to be getting ignored now but I'll ask anyway

I'm getting 60ohms from the back wire removed from the ignition coil to ground. When I pull the G2 ignition relay it goes to 1.

I assume since this supplies the 12v power for the spark that it shouldn't be getting any resistance, right? I got the same 60ohm ground from pin 87 of the G2 relay and followed it to fuse 18, which never blew but is still seeing the same resistance on the "cold" side which goes into the passenger harness and into hell.

marc abrams

I don't have any wiring diagrams for the later cars but I won't ignore you. Those ohm readings mean nothing. What I would like you do is to get voltmeter with alligator clip leads and place one lead on the starter battery terminal and the other lead to ground somewhere on the starter and note the voltage for both cranking and when you are just getting the clicking. It should be close to battery voltage. I have a gut feeling its something with your cables.

1987Porsche944WithRealLongName

So I'm getting a reading from post 50 on the ignition switch connector to ground.

This goes to the starter/alternator wire, which was the one that originally shorted and caused this whole mess. I tested it several times to make sure it's fine, so I checked the solenoid post that the small red wire connects to on the starter. It's getting a ground signal.

Is this post supposed to be grounded via the starter case to bellhousing?

marc abrams

No, the #30 is the battery.
You can't check the battery cables with a ohmmeter, only a volt drop test works.
You want to be sure you are getting power from the battery down to the starter, you know its getting power from the ignition switch because its clicks.