Alan

There aren't any - in any case with those its a one way trip...

Bill from what you describe its isolated to the battery itself (internal issue) or more likely (since I assume you jiggled the cables but didn't really jiggle or remove the battery itself) the positive supply to the ~Starter.

Have you tried a new/alternate battery - I'd swap one in first - easy to test.

It clearly isn't an alternator issue - since you say it stays running well once running and so the wiring from the Alternator to the Jump Post and Jump Post to CE sounds fine. So most likely remaining is the Battery to Starter cable. It could also be the cable from the Starter to Alternator/Jump post.

You can try to test for voltage as Jim notes - do this with ignition on - but this does require the car cooperates and fails while you are ready to test...

You could also strip back the sheathing from the ends (start battery end on Bat/Starter cable) and see if its heavily corroded (my guess is right there if you get this far).. If its not these then you can use HD heat shrink tube to repair the ends.

Alan

SeanR

That's what crossed my mind also as I was reading.

James Bailey

Lots of times people wiggle, jiggle,pry, pull off or pound on battery terminals and end up damaging the post internal connections. The fact that the battery has been touched several times increases the possibility..

SeanR

Bill, do you know how old the ignition switch is?

RET

Just repeating what has already been written: test with voltmeter progressively if the car has obligingly failed at your convenience (between battery posts, positive battery post and ground, far end of positive cable and ground, etc.) until you find the open circuit, or if the problem does not cooperate, replace the battery to see if problem does not return in the future.

FWIW, the battery in my boat caused a fairly similar problem: all seemed well and everything worked as it was supposed to (fans, lights, other low power items) until the starter was engaged and then all power disappeared; fiddling with the battery cables brought power back until the starter was engaged again, which immediately caused the battery voltage to drop to zero. A kick to the battery brought voltage to normal as did turning it on its side or upside down (it was a gel cell, not a flooded battery). Many repetitions produced the same result each time. OTOH, this battery never again was able to start the motor, unlike the problem you describe.

Good luck.

Bob

928 at last

I had a battery act up with internal shorting in another car a while back. I'd do the voltmeter test at the terminals and work forward while it's acting up, or just replace the battery with a known good one for a while.......

Alan

Lots of talk about internal battery shorts - thats not really very likely here.

An internal battery plate short will rapidly cause that cell to discharge - possibly overheating and damaging (even exploding) the battery. Its not usually recoverable, battery becomes pretty useless (voltage drop, usually also accompanied by higher internal resistance due to secondary effects).

A battery open circuit is more plausible here especially related to terminal physical damage. In this case messing with the terminal itself, or battery movement or heat or current loading can all cause changes in the behaviour. Heat being the most likely explanation of purely temporal changes.

e.g. let it sit and it fixes itself...

Alan

Bill Ball

The battery is getting a lot of press. So far, the battery looks good to me. When the electrical system was dead, I still measured ~12.7V across the posts, even when seeing only 2-4V at the jump post. And then there is the report by the owner of no response at all to a jump with an external battery.

Having dealt with broken posts before, I've tried to wiggle the posts and have seen no change in battery voltage and there is no movement in the posts. AFAIK, they haven't been pounded on. I could not reproduce the problem by manipulating the battery posts.

Doesn't the lack of response to a jump at the jump post implicate the engine harness? It's a little confusing to me. I gather from the wiring diagram that the battery positive cable goes to the starter, then via the engine harness to the alternator and the jump post. If the battery ground is good, for the battery not to provide any power, I would think the section of cable from the battery to the starter would be implicated. For the jump post to not start the car, I would suspect the engine harness. I have to double check that the owner actually tried to jump at the jump post rather than at the battery itself or is there a cause that would account for both failures?

If just the battery is bad, I would still expect a jump with an external battery to do something.

Alan

Yes it would seem so If the section between just the starter and alternator is bad it would account for both... depending on the wiring - some cars have Alt to Jump Post and Alt to Starter sections - some have Alt connected to the Starter and from Starter to Jump Post, so depends on config. WD shows all connected at Starter on an '87 - do you have 3 terminals on the starter big lug or two? How many terminals connected to the Alternator B+?

yes and if the battery cable to starter is bad ditto for a jump from the jump post. So a lot depends on whether the jump start attempt was at the battery terminals or jump post?

The chassis to engine block ground is not a culprit - could be for other issues like no starter action - but not for total loss of CE power.

Alan

James Bailey

As recall the wire to the jump post is not really a heavy enough gauge to flow enough power to start a 928 with no battery.....it is not battery cable. Jumping there is to assist in starting a car with a low battery.

Alan

It's not ideal I agree - but its short - certainly the starter should do something if the connections/wires are generally OK.

Alan

hacker-pschorr

My 81 was acting similar to this car, ended up being the green (or is it yellow) wire that goes from the jump post to the starter was badly damaged under the harness cover. Pulling back the insulation it was badly frayed. It's amazing my car ever started.
After replacing that wire it spun over so fast i thought valves were bent.

Alan

Not quite true... Assuming the battery is good the ECU's will be getting power anyway from the battery (while discharging) so it means nothing about the continued goodness of the battery to starter to alternator segments - only that the alternator to CE is good.

Now if the battery goes out of the alternator circuit its quite likely that the voltage regulation will be very poor - voltage stabilization, level and ripple noise will all get worse. You may get more radio interference/noise, higher/erratic readings on the voltage guage... any of this ring any bells after running for a while...?

Alan

jcorenman

Good point, the battery is happy to power the ECU.

Bill did report a higher voltage at the console voltmeter at one point so that fits.

the flyin' scotsman

Issues with the large capacitor, battery would add voltage spikes/ripple..........simple exchange should verify possible issue.