Hello, I have a 1984 928S that was meticulously maintained for 20 years and has suddenly turned into a lemon (I bought it 8 mos ago). It has had multiple electrical problems that keep killing the engine. Almost everything has been diagnosed and tested by one of the Big 3 and everyone is now at a loss about what to try. The current symptoms: driving, probably fast, turn on the headlights, complete electrical failure. After gliding to the breakdown lane, usually in between speeding trucks with no gas pedal, the car will fire up again.

Any thoughts and opinions are greatly appreciated. I'm just looking for chatter. As I said, one of the Big 3 has had it for two weeks and they're stuck.

Thanks.

 

Kind of hard to give advice that's probably already been done. It would help if we knew everything they tested or did so we could ponder this futher.

 

Randy V: This thread should be linked with

https://rennlist.com/forums/928-forum/203629-car-dies-when-i-turn-on-headlights.html

another 84s that dies with the lights are turned on.

 

So.... driving down the road.... you turn on the lights. The lights pop-up? And then the car dies when the lights come on? Or the car dies prior to the lights reaching the 'up' position?

With lights up? Or lights down? On? or Off?

This line of questioning is an attempt to figure out if the problem is linked to the lights themselves or the motor that raises them. (Gotta start somewhere...)

 

Sharkskin's Rx for gremlin eradication

HTH

 

What if you take the lights motor fuse?
Klim

 

Hand crank the lights up and see if the motor dies?
jp 83 Euro S AT 49k

 

Hi just a thought look at the wire bundle that runs next to the light bar that runs across the front of the car and see if any wire harness is rubbing on the light bar as it transitions, could be a worn through wire bundle that is grounding pay particular attention to the the ends of the bar where the linkages are, another thing to try is disconnect the light motor and turn on the lights, this will tell you if the problem is in another part of the wiring harness or light switch. good luck, Stan

 

Wow, that is a strange problem. Mrmerlin is on to one train of thought - the physical movement of the light mechanism causes wiring problems.

Try this, unhook the connectors at the headlamps. During daylight, drive the car (in a safe place) and now turn on the headlamps. If the engine doesn't die, you've confirmed it is an electrical issue related to headlamp current flow. If it dies die, then it is likely an issue with a physical wire chaffing around the headlamp system.

If it is related to headlamp current problems, I am thinking along this line .... As you know, there are + 12V connections to all the electrical gizmos, and the return path to the battery is via ground connections to the chassis and then through the chassis to the battery. When any connection gets dirty, resistance increases and there is a voltage drop. When a ground return circuit is corroded or broken, the current "looks" for different ways to get back to the negative terminal of the battery. If the main path is corroded (very high resistance) or a wire is broken, the current takes different paths and those paths may not have the necessary current capacity.

My guess is you have a ground problem or connector corrosion problem. There is "just" enough current capacity for the 928 to run when the lights are off. When they are turned on, there is a large voltage drop SOMEWHERE and the engine electronics stop working.

I suggest a very good look at ALL connectors, ground points and all ground wires (brown ones) - their connection to the chassis and at the battery connection to the body (rear) and at the battery terminal itself. There are many ground points BEHIND the fuse panel, you need to take the bolds loose and move the fuse panel for access. There are many plugs that go into the fuse panel. Remove and clean all those connections.

Inspect at the connections at the L-Jet fuel module and the spark coil and spark box. Check voltages with and without the lights on.

Another possibility is your alternator. If the diodes are marginal or bad, they could drop out .... though the battery should be able to source enough current.

Yet another but much less likely possibility, a short in the headlamp switch or wiring. I would think that there would be some bad smells of burning stuff - but a voltage drop is likely the cause of your engine electronics to cut out.

 

All good suggestions. Sorry to have been so glib in my earlier response.... but if you have lots of gremlins, you really should disconnect the battery and take a look at the backside of the fuse panel. I pawed through a whole stack of fuse panels at a dismantler while looking for one I could cannibalize, and just about every one of them had some wires across the back with melted insulation. This can cause shorts in the panel itself, resulting in any number of problems. Granted, that wasn't a fair sampling since all of the panels were from junked cars.... but still, I think it's worth a look. On an 84, I don't think you had the power wires attached at the top of the panel like later cars, and I think it should be easy(4 small screws) to get a look at the back side. Get a strong light and try to look past the surface wires.