A buddy has an 87 that periodically has no electrical power, or very close to none. I posted a thread earlier and it appeared the consensus was a bad ground or positive cable or junction. Based on some faulty testing I suspected a bad battery ground cable. A new one was ordered and installed. Still no power. I removed the positive battery cable clamp. The post and clamp looked corroded, so I cleaned them up, and BAM - we had power.

I thought the problem was solved, but a week later the problem returned. When I went over to look at it, the car had power, started and ran well. I had planned to clean all the grounds and positive junctions, so I took the car to my house and proceded to do so. I didn't find anything notably corroded or loose. I began to drive the car back to my buddy's place, stopping once along the way. After that stop, the car had no electrical power again. Eventually after some fiddling around the battery compartment, power returned and I drove the car the rest of the way to his house, puzzling over what could possibly cause this.

Here are the symptoms:

1. Periodically there is no electrical power at all or close to it. I noticed that clock seems to work, but none of the lights or anything else does, and when you turn the ignition on, even the clock goes off. I have measured a 2 to 4 volts at the jump post during these incidents.

2. The car has never stalled once started. The problem only seems to appear when the car is sitting.

3. When this happens manipulations of battery and cables seem to resolve it until the next time, which could be weeks, days or hours later. This might just be coincidental.

4. During the incidents the battery shows good charge state and there is no evidence of a broken post or other battery problem.

5. I didn't personally verify this, but the owner reports that there is no response to a jump applied to the front jump post during the incidents.

6. Today I noticed the volt meter periodically jumped to close to 16 volts while I was cruising. I was going to measure the actual voltage but by the time I got to my buddy's house it had stopped doing it and showed just below 14V at cruise speeds.

So, there may be a problem with the voltage regulator, but I don't know how that would account for the main problem. My simple mind says there must be a problem with the main positive battery cable, isn't it strange that the car never loses power while driving?

HELP!

 

That's what my simple mind says, too. Or corrosion at the power terminal on the starter.

Not strange that the car runs fine when running. The alternator provides all the power (plus battery charge) when running. The circuit from alternator to battery is only used for charging once the car starts. Focus your search there.

 

Shouldn't there be full (or close to accounting for resistance and depending on what you ran the voltmeter between) battery voltage between the positive post and the engine block or strut tower? I would investigate the charging and starting circuit further. Maybe a frayed cable somewhere?

These intermittent problems are always the most costly and frustrating for shops. I was reading "Canadian Technician" and there was an article about an Explorer with an intermittent problem, every time this woman picked up her kids from school on Wednesday at 4PM, and loaded their crap into the back, when driving, all the dummy lights that initially show during start up would intermittently flash going over bumps. Well, long story short the tech found that one of the kids tuba was constantly pinching a wiring harness and it frayed, causing an unintentional ground.

 

Hi Glen:

I cleaned the terminals at the starter and alternator. I'll focus on the positive cable. Since as you pointed out the alternator is supplying power while driving, does that rule out the engine harness between the starter and alternator and jump post? The problem might be near the battery since manipulations in that area SEEM to help sometimes. Other times, it resolves just by sitting for a while.

 

What about a fusible link handling too much current? I don't know a whole lot about the 928 specific electrics, so i don't even know if 928's have fusible links in the charging circuit, but if power comes back after it has time to sit, that could be a fusible link cooling down couldn't it?

 

Try taking off the ground strap from the motor to the chassis at the steering rack. I found one of my cars here that the bolt had corroded inside the hole it looked perfect from the outside but once I took it apart there was so much corrosion i'm surprised that it worked at all. I chose a longer strap and used a different bolt hole to fix it. good luck

 

If it's a frayed wire, it's inside the sheath. I looked at the whole length of the positive cable and didn't see anything, but now that the problem has reappeared, I need to manipulate the cable and see if I can recreate the loss of power. So far it just happens at random.

 

I wish I had found that. I cleaned and applied Deoxit to all the grounds. They look fine now.

 

AFAIK, there are no fusible links.

 

Ok. I encountered this in the shop i work at recently, so that's why i suggested it.

 

I had the same issue with MY87 last week, turned out to be the ground cable for the battery. Good luck.

 

For grins I would swap in another battery. Also, check the grounds in the spare tire well as well as the wires on the connectors.

 

Bill, I had a similar situation on an MY85 once. Turned out to be a loose connection at the hot post in the engine bay. Might be worth checking if you haven't already.

 

This is what I am thinking...

If it runs reliably once started, then you know that all of the wiring from CE panel to jump-post to alternator, to starter, to battery terminal (where the EZK and LH get their separate power) is all good. The alternator is supplying the voltage and it is being properly distributed everywhere.

The battery itself is only needed to start the car. Once started, it just sits there accepting charge current, and if you disconnect it then I think all that would happen is the alternator-voltage might go up a bit (less load).

You've checked the battery terminal carefully, but consider a broken connection internal to the battery: It might make contact, or not, or only poor (high-resistance) contact, but fiddling with the battery would likely change that.

It could also be the ground strap from battery to chassis, but you've checked that also.

A good definitive test when it is "playing dead" would be to put a voltmeter directly on the battery posts (not the terminals) with key on (i.e. some electrical load). If you don't have 12 volts there, then something is open-circuit internal to the battery. If you have 12-volts between the posts then start moving the meter probes outwards and find out where the voltage goes away (key on)... positive terminal to chassis, starter to chassis, etc.

Good hunting!

 

Sounds to me like the battery has an intemitent short.

The car is fine when running so as Jim mentions the charging system and wiring is correct.

Try a known good battery........good luck.