USArmy_Medic

Hey guys, this unfortunately is my first post. I have a 1983 928S, I recently had to change the battery because it had sat for a few months while I was away from home. I couldn't find a battery to match the length of the stock, and ended up using the shorter duralast battery.

anyway when I was making the turn onto my street (thank god I was so close to home) my negative terminal slipped off of my battery, there was a large surge of power (as evidence of my headlights getting much brighter and I heard my relays make a noise) and the car died. Well I went and replaced the fuel pump relay, and the EFI relay but the car still wont run longer than 2 seconds. I will start, but will die shortly there after, and I can hear the fuel pump whining after it shuts off.

I'm assuming since the owners manual says that disconnecting the battery with the car running will damage the alternator, that my alternator needs replacing. On a side not, when I put my flasher relay in it screams, and I can feel it vibrating like crazy so I have left it out for now.

Can you guys shed any light on my situation? I really appreciate any info that can be offered. Thanks ahead of time.

Landseer

Can you say what year the car is?
That would help folks to help you because they have different wiring set-ups by year. And USA cars are different sometimes than gray market or rest of world cars.

9two8

....he tells you in the first line.., Quote-- ( I have a 1983 928S )


Ken
80 928 S
5 Speed

UK

Landseer

Jeez. Impossible to miss. Embarassing. Sorry.
Do you happen to have a digital voltmeter?
That would help.

John Speake

I believe your car is an L-Jetronic. Without a battery connected, you would have very high volts applied to all the circuits, maybe more than 16v.

I would suspect the L-Jet ECU brain. Try to borrow an known good L-Jet ECU.

Landseer

Logic would say it could have cooked the brain. But you have an awful lot of other things to work through, fairly simple, that if nothing else are prerequisite to keeping the car solid. You said its been sitting a while, I assume outside.

If your grounds haven't been cleaned in a while, a voltage surge can further disrupt them,too.

Might be a good time to take a quick time-out, clean the grounds (5 in particular) and pull the CE panel to inspect and clean and replace the fuses. Look at the back to ensure no melted wires.

5 grounds I'd target are neg strap to body; 2 located just above CE on firewall inside car; one under car on pass side connecting block w/frame, and the important injector harness ground on the pass side cam cover hiding under the emissions piping.

Bad ground can cause relays to behave like you describe. Bothers me that the flasher relay (# V) is doing this, so you may have more things going on at once.

Is battery voltage still above 12V?
Little positive wire on battery clean? It feeds the brain John spoke of.

I'd also not discount the injector relay. A Y-shaped wire jumper should be tried to bypass it. The reason is sometimes the actuation circuit voltage isn't sufficient to trip a known good relay, due to other causes. So getting the car to run on a jumper eliminates other variables and lets you concentrate on the causes.

You could also be suffering from an ignition switch that's failing.

Lots of possibilities here. Dr Bob, also Alan, have both posted a lot of great troublshooting tips on electrical situations like this, search with advanced search if they don't chime in directly.

Fogey1

Rather than putting a known good ECU in your car and taking a chance of burning it out, it's probably better to put your ECU into a car that runs to see if it still runs after the swap. Of course, doing it that way is less likely to send business John's way.

Where are you? To do a swap at all, you'll need a local owner with a running car. BTW, Autozone sells the right size Duralast.

USArmy_Medic

Hey guys thanks for the tips. No unfortunately I don't have a voltmeter,guess I need to add that to my tool list, especially with the electrical nightmare these cars can turn out to be. Also, I'm in New Orleans, I've seen a few 928's around, but I don't know the owners personally.

Alan

Failure mode still sounds like a fuel pump relay issue - try running with fuel pump relay 30-87 bridged - does it run OK then? did you get the right replacement fuel pump relay (year specific).

Yes you need a voltmeter - I thnk its a bit unfair to blame the car for this one...

Alan

SteveG

Alan is being diplomatic and going strictly from your handle, I'm guessing you were TDY, and you get home, you want to jump in and go. BUT knowing what "nightmare these cars can turn out to be" and still letting the ground strap "slip" off, may be a self-inflicted wound: perhaps it needs to be pointed out (any newbys out there?) that:
1. the battery needs to be correct size, some people have had batt short against the cover.
2. the battery needs to be secured properly, see above.
3. the ground strap (all connections) needs to be secure.

If you have a battery disconnect switch, never disconnect while engine is running.

USArmy_Medic

I ordered the relay from dC Auto, and the car ran fine for about 16 miles with it until the spare knocked the battery cable off. And I don't blame the car at all, I just hear that the 928's were plagued with electrical problems from a lot of people so I agree that I should already have a voltmeter. Besides, I love my car too much to blame it, yeah she catches an attitude every now and then, but that's just proof that she does have a personality.

Dennis Wilson

Had a problem like this on my 78 5 speed and upon investigation discovered the positive batter cable had been routed through the shock coilovers. As a result, any dip of the rear end pulled up on the cable battery connection. A new cable and proper routing fixed it.

Dennis

Alan

So sounds like the new fuel pump relay was before this happened? In that case I'd say its highly likely this is the issue.

The fuel pump relay on this vintage has 2 parts a 'primer' case and a 'run' case.

When you first turn on the ignition you get a burst of pump activity to prime the fuel rails - then the relay turns the pump off. The relay subsequently only turns the pump on again when it detects the engine rotating. This is a safety interlock - if the engine ever dies (e.g. accident) the fuel pump shuts down

It seems likely you fried the circuit in the relay that detects engine rotation and you are running briefly off the initial priming pressure only.

Test is the same as above bridge 30-87 on the fuel pump relay socket to get the pump to run continuously and see if it fires up & runs.

Alan

Fogey1

One of the great perks at a lot of bases is an automotive hobby shop with lifts and tools and so forth. It's worth checking for if you're on or near base and on active duty. "So forth" is also likely to include guys who know what they're doing.

USArmy_Medic

Yeah it would be great if I was still at bliss, but nothing close enough to me here in New Orleans.

Can anyone help me out with a link to this relay jumper so I can try it out.