Musse

Two steps forward one step back!

Bringing my -90 GT back to life is progressing nicely but I am struggling with identifying the source of the latest challenge.

As I was attempting to turn over the engine with the starter the first time to build oil pressure after the rebuild. I turn the key and the started doesn't engage. The rest of the dash lights up, the windows, sunroof, and other items work. We then check the stater and the solenoid and the starter has power, but the solenoid does not when turning the key to engage it. So it's not getting power from the 14-pin connector (yellow cable if I remember correctly)

I tried the trick of switching the starter relay with the defroster relay (XIV), and as I did that, there was no change. However I noticed at the same time that the red cable that goes to the 14-pin connector was warm (see screenshot of the cable below, it's not from my specific car), and there was white smoke coming somewhere from the front driver-side of the engine (opposite side of the 14-pin connector). I then quickly disconnected the battery as I was afraid to fry something.


Circled cable was getting warm


I am a bit afraid to reconnect the battery again to continue investigating the solenoid issue. Some of my questions are:

- I have cleaned some of the ground points, could this be a cause of the issue?
- What could be the cause of the white smoke?
- Where should I begin to safely identify the source of these gremlins?

I've had the entire engine out of the car and rebuilt, so the chances of my connecting something incorrectly is high (likely 100% at this point)

Thanks for all the help in advance - sorry for these seemingly stupid questions. I am still learning the ins and outs of 928s (enjoying it despite these challenges

- Chris

gazfish

You can take the 14 pin connector apart to check there’s no stray wires shorting the pins and check you have the correct wiring on the starter motor. Most likely the harness need replacing, moving it during the engine removal may have caused a short where the insulation has failed.

SwayBar

The first thing I would do is track-down the wire(s) which were smoking and fix it, and then determine why it burnt. It should be easy to find since the insulation has burned off and why the smoke.

I had this happen to me once when I replaced a relay, smoke next, and found the burnt wire in the electrical panel in the bottom row of one of the colored connectors.

Musse

Progress is being made!

I opened the 14 pin connector and it looks good IMO. Nothing fried thankfully

I also found this cable, which I had assumed was ground and that is connected to the coil bracket on the passenger side (2nd picture). Any idea where it should be connected?


Black cable that was unconnected

Other end of the same black cable I had grounded against the bracket on the same side (passenger side)

Musse

Found it. It's the lift loop behind the cam cover.

But am I right in assuming that this would not cause the short circuit and faulty solenoid I experienced?

davek9

All those connections are oxidized, and need to be treated, either Dioxit or a light coat of wd40, (note WD 40 is conductive, disconnect battery, spray wipe off excess).

FredR

The starter relay is a typical 053 relay but the defroster relay is different- whether that is the cause of your problem I have no idea but if the smoke started after changing over the relay then that has to be more than coincidental.

The solenoid on the starter motor is driven by the yellow cable in the 14 pin connector- when that solenoid engages power from the battery is switched to the starter motor that is subsequently energised. When the key is turned to the starting position bus 50 is energised and you should be able to see 12 volts on that yellow cable terminal on the 14 pin connector. If power is geting through and the solenoid is healthy the motor will crank.

As for the smoke you saw you need to take a look at the power cables entering and leaving the main post on the alternator. At this stage just about every example kitted out with the original engine harness wiring is going to be in poor condition- yours does not look too bad compared to many I have seen - at least one can see the colours but that does not mean the cores are OK.

Musse

Thanks Fred!

I jumped the yellow cable in the 1st position of the 14 pin connector to the post and the solenoid engaged and the engine cranked. However after about ~ 1 min smoke was clearly visible again and we aborted. As you point out the smoke seemed to come from the alternator and also I noticed a few cables leading to the bottom of the fuse panel showing signs of being slightly burnt, not great. I will check the cables going to the alternator as well but I wouldn't know what to do if they were damaged.

At this point I am way out of my depth so I'll try to find an experienced 928 workshop around the south of Sweden where the car is stored to do the diagnostics. I am afraid that I'll attempt something that will damage the wiring even more.

Thank for all the help everyone! Truly appreciated!

karl ruiter

The cable coming off the 14 pin connector to the engine can be subject to a lot of internal degradation. There are four types of wires in it: Smallest, slightly larger, big, and huge. (At least in my '88) The smallest wires hold up pretty well, but all the others can tend to lose their jackets after a time. It does not always happen, but it can be very dramatic when it does.

Mrmerlin

make sure you disconnect the battery till the issue has been investigated and fixed

Musse

Today I continued trying to identify the source of the electrical smoking in the engine bay, and also checked the alternator, starter, and cables to both.

Beginning with the alternator, I saw no sign of heat or burned cables. I did however see that the ground cable was severely oxidized. I missed this when reinstalling the engine but it is now clean.

Both cables look fine from what I can tell

After cleaning the ground cable oxidization I continued investigating


I followed the harness to the starter. As mentioned earlier in the thread, there's power to the starter but not to the solenoid when I turn the key to start. But if I jump the pin in the 14-pin connector to the post the solenoid engages and the engine cranks. As far as I can tell, there's no sign of damage to the cables. I removed all three, cleaned, and reinstalled.





My biggest breakthrough was however that I am pretty sure I found where the smoke came from that I saw in the engine bay. It appears to have come from main cable bundle (the front of engine harness).

Does the damage circled in red look like how a short circuit burn would look like?


Here the damage is most visible. I followed the cable bundle and this was the only place wher I could see it.

Another view of the same damage.


I didn't have time to continue following the harness back to the 14-pin connector from on top (my engine lift blew a relay and I couldn't lower the car - seems like electrical problems are following me around )

If this is the damage I saw in the shape of smoke - what could be the cause? Could it be cables inside the harness budle where the insolation has worn off and they are shorting? Could it be that the bundle has worn through the insolation and 12v goes directly to the block somewhere?

It seems unlikely that the oxidized ground cable in the alternator would cause this...

Is the nest step to just order a new front of engine harness? Or am I risking wasting money if that burns as well because core issues is somewhere else?

FredR

The small cable on the alternator is not a ground cable [if that is what you infer] - it is the exciter cable, should be coloured blue and goes to pin 1 on the 14 pin connector if my memory is still working correctly.

You need to determine why voltage is not getting through to the solenoid- could be a problem with the ignition switch not energising the bus 50 connection when the key is in the cranking position. You might do well to test the resistance from the yellow cable pin [in the 14 pin connector] to earth. It should indicate a very high resistance value as in no current flow potential.

I would not order anything until you have determined the root cause of your problem. The electrics in this part of the system are prone to age related degredation as discussed earlier and time based replacement is an inevitability but yours may still have some life left in it.

gazfish

There should be a square rubber insulation piece glued to your oil pan that prevents the starter motor big cables shorting to the engine, it looks like it’s missing in your photos. Can you see clear space between the cables and sump. Might not be the cause of your issue but it’s a safety item.

Phatslax

From my experience with a 1981 euro I would check the whole loom from the 14 connector to the ancilliaries. Mine was completely rotten, to the extent that there was no insulation left. Multiple availability of shorts.

Alan

They are the same '53B relay on a 90' model year - so its unlikely a relay issue. I suspect the starter relay not engaging likely has nothing to do with the smoke, are you sure the smoke isn't just from oil on the manifolds burning off?

I'd suspect your starter doesn't engage because the starter relay's 85 connection is not getting grounded by the trans switch (neutral/park safety swicth). This connection is in the spare tire well behind a plastic shield above and in front (wrt the car) of the battery box. There is a 6 pin connector there (the starter relay pin 85 connects on Pin 4 a Violet/White wire. It must be grounded for the car to start). If the trans has previously been out the switch may not be connected properly. If its a manual it should be permanently grounded.

Alan