tricky electrical puzzel

[Glanceb]

I recently got the car serviced, and it ran really well for about a day, driving it in the rain I noiticed that the horn hard stopped working which wasn't an overly big issue and I kept going. After driving the car around for a while the whole car went dead while driving and stoped, no power nothing it was baisically like the life had been sucked out of it.

I then tried a jump start which worked but at higher revs the engine is now misfiring and has an unusual rythm.

Next step was to check the spark plugs (all ok), the altenator (ok), so I wanted to double check the altenator so while the car was running I disconnected the battery which caused a dead stop again.

I always assumed that once a car was running the battery could be reoved. I tried the same battery removal while the car was running on my VW Karmann and the engine kept on going. Is this a normality with the e9 or do I have a major problem somewhere?

 

[jmackro]

I recently got the car serviced, and it ran really well for about a day, ...

Glanceb:

I can't explain your coupe's problem from the information provided - it's pretty hard to diagnose these things over the internet. But, my coupe had a similar problem a couple months back, so I am fresh on debugging these things. A few thoughts & questions:

- Tell us more about "recently got the car serviced". What work was done? Anything electrical? Your problems could just be a coincidence, but the timing is suspect.

Next step was to check the spark plugs (all ok), the altenator (ok), so I wanted to double check the altenator so while the car was running I disconnected the battery which caused a dead stop again.

Yes, the car should keep running when you disconnect the battery. So I question whether your charging circuit is really ok. Tell us more about how you checked the alternator? Was the voltage regulator also checked?

For what it's worth, the voltage regulator was the component that failed on my coupe - that failure caused the alternator to put out too high a voltage, which destroyed the battery, Pertronix ignition, gauges, and the "load shedding" relay that powers things like the headlights.

 

[Glanceb]

tricky eleectrical

I assumed that if the alternator had a problem the light would appear on the dash. When I put a multimeter on the terminals of the battery it is only readin 9v??

Where abouts is the voltage regulator and what tests should I do to check the altenator?

I appreciate the help, I'm starting to believe the saying BM trouble you.

 

[Glanceb]

tricky electrical

Actually now that I think of it when the car was serviced they changed the spark plugs oil filter, oil etc. Basically a general service was done. I do remember when I picked up the car the odometer started working again but then stopped, the rev counter doesn't work and never has nor does the clock?? Would this be the regulator? I am not good at electrics at all so this has me a bit worried.

 

[MMercury]

I recently got the car serviced, and it ran really well for about a day, driving it in the rain I noiticed that the horn hard stopped working which wasn't an overly big issue and I kept going. After driving the car around for a while the whole car went dead while driving and stoped, no power nothing it was baisically like the life had been sucked out of it.

I then tried a jump start which worked but at higher revs the engine is now misfiring and has an unusual rythm.

Next step was to check the spark plugs (all ok), the altenator (ok), so I wanted to double check the altenator so while the car was running I disconnected the battery which caused a dead stop again.

I always assumed that once a car was running the battery could be reoved. I tried the same battery removal while the car was running on my VW Karmann and the engine kept on going. Is this a normality with the e9 or do I have a major problem somewhere?

We have all been daunted by the vagaries of old cars, but rather than reinventing things, do you have a basic auto primer of some sort? Your mystery could be any number of simple things.

But first, read this: "Warning!
Some people tell you that you can check your alternator by disconnecting it from the battery to see if the alternator can produce enough current to keep the engine running. BAD IDEA! Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.
Simple Test: If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle." From: http://www.bcae1.com/charging.htm

Based upon what you have said, here is a good place to start:

http://www.cscoupe.org/tech/autobooks/chapter12/gallery.htm

 

[jmackro]

I assumed that if the alternator had a problem the light would appear on the dash. When I put a multimeter on the terminals of the battery it is only readin 9v??

Where abouts is the voltage regulator and what tests should I do to check the altenator?

Glanceb:

The advice that MMercury published is good. His post addresses your question on how to test a regulator (see the text at the bottom of p. 128 that MMercury scanned and posted). The regulator is mounted behind the battery - the pictures that MMercury posted show what it looks like.

The fact that the light isn't glowing doesn't mean that the alternator-regulator-battery are all A-OK. Heck, the bulb could be burned out! The bulb catches most failues, but isn't 100%

MMercury is right - you shouldn't disconnect the battery while the car is running. However, if your car is simple (like my carbureted 2800 CS) with no electronic components, damage is unlikely. Don't try this on your 2009 Lexus! Again, I was less advocating disconnecting the battery as a definitive test, and more replying that "yes, the car should have kept running".

I am not good at electrics at all so this has me a bit worried.

Well in that case, discretion may be the better part of valor. Just drive the thing to your friendly neighborhood classic BMW repair shop and hand them your Visa card.

 

[abe3.0CSi]

Make sure ground to car is okay.
abe

 

[jranmann]

I agree Abe it's likely a major 'ground' fault as BMW links the grounds in groups according to the system diagrams on my e24. the Rain, etc and previous work by 'mechanic' all spell trouble...

I often hold my breath as I leave my e24 Coupe for repairs as it often comes back more distressed than when I leave it...

Hazards of ownership I suppose...

Cheers...

 

[Glanceb]

tricky electrical

Thanks lads, I will have a look this weekend.

The visa card and a classic repar shop are a good idea only in Ireland they are few and far between (the classic repair shops)

Cheers.