flyboy1717

Good Morning,

My car (92' tip) has recently developed a new problem. Periodically, while driving, at any speed/rpm, I have been experiencing what appear to be dips/spikes in voltage. The dips are characterized by all systems dimming/shutting down (headlights, dashboard back lights, radio, cigarette lighter (radar detector). The car hasn't stalled yet, but has come pretty close. I abandoned my trip the other night to check the voltage of the charging system. When I first measured the voltage at the battery, at idle, engine running, the voltage was approximately 12.60, which would indicate a problem with the charging system. This did not change as I increased engine speed. After turning the car off, and back on, I was able to record 13.80 at the battery, indicating the alternator was now providing a charge to the battery. I wasn't able to replicate the low charging voltage again. So my questions are:

1.) Have others experienced what I'm calling a dip/loss in electrical power.

2.) Have others had an alternator/voltage regulator fail with similar, inconsistent readings on a multimeter.

3.) In Adrian's book he calls for measuring AC voltage in the DC system to see if the diode packs in the alternator have failed. How is this measurement done. I measured AC voltage across the battery terminals while running, however my meter was simply interpreting the DC voltage as AC (13 V DC, makes the meter think its 26V AC). Is there another way to check for this voltage without using an ocisloscope?

4.) Am I headed down the right path by removing the alternator, or should I be checking for other issues first?

Thanks for any insight.

Roger

Rocket Rob

Check your ground cables. There is one at the battery and another between the starter and the bottom of the car. A loose ground could cause this.

flyboy1717

Rob,

Thanks for the response. I was able to check the ground cable between the battery and the body. Everything looked clean and tight, but I did take the connection apart and cleaned it again with a wire brush.

I wasn't able to get up above the starter to check the ground cable there. I'm a little confused at how this could cause my symptoms, as I would think that this ground is only used when the starter motor is being used. I will try to get up above the starter this Saturday and hopefully find a loose wire which would be the "smoking gun" for right now. If I can't, I may just continue driving it and see if the symptom reappears.

Does anyone else have any ideas/input.

Thanks,
Roger

meek

Roger, there were a couple of posts recently that discussed similar issues to yours, one of which was my car. In the end, it turned out to be the power supply from the fuse board to the ECU. The wire was intermittent, as was the problem and a pain to diagnose. The ECU was checked early on and was all OK, then checked again a week later and wasn't. Not sure why the power wire degraded as it is still in the car; the mechanic just ran a new wire through rather than strip the loom apart to take out the old one. Good luck with your hunt.

PS my symptoms were not consistent i.e. power would cut out entirely on the move for a fraction of a second, dash lights all on etc., but the motor would keep running. Sometimes it would cut out all together and leave me stranded.

flyboy1717

Adam,

Thanks for the reply. I just checked out your thread, that did sound very difficult to eventually find.

My symptoms sound slightly little different, as I've never had a problem starting it (yet). My problem usually occurs while driving, and the electrical power will "flicker" on/off for a split second for 3-5 times, and then seem to resolve itself.

Regardless, I will do a visual check of the loom leading to the ECU, though I think its taped up pretty good. Also worth noting, is that I recently removed the soaking wet foam from the drivers side (left hand drive). I believe this foam also protects the loom going to the ECU in addition to soaking up water. Perhaps I disturbed something getting in/out of my car. I also haven't resolved the water intrusion problem yet, hopefully the water which was previously being captured by the foam isn't being captured by the ECU.

Thanks for pointing me to your thread. I will spend some more time with it this weekend. One of the frustrating points of this problem, is I can't recreate the problem on demand. I've drive over 100 miles without it happening...

Thanks,
Roger

Rocket Rob

This second cable, grounds the engine to the chassis. Your battery won't get power consistently or poorly if this connection is bad.

Alex Sol

Raising up an old thread. Had this same issue where I was only getting 12.5 volts and slowly draining down. By 30 mins of driving i'd be down to 11.9 volts. and then park on driveway. Come back out and no start! Did some testing. Trickled the battery to full. Started and removed the positive terminal. No change in voltage hovering around 12.5 volts. Hooked up Oscilloscope and waves were very choppy and had large variation in voltage. Assuming it was alternator, I purchased rebuilt and slapped back in... (yes I slap stuff vs install). Start up and exact same voltage. Broke a battery terminal, bought new and replaced. Slapped in a brand new battery (Costco Special for Honda civic size). No difference. Read this thread and decided to check grounds. Battery Ground in Frunk no problem. Ground from Starter to Chassis behind the passenger side Rear Wheel area was loose on the starter side. Snugged up, Started and boom, 13.5 volts. Swapped out new battery and slapped in old. Same 13.5volts. Called the Alternator shop and asked for my core back. And solved a problem where I was making very little power above 4,500 rpm meaning it was spooling up very slowly to redline. Happy again in Porsche Car DIY. Thanks to the contributions of this community!