Weird electrical problem. Help sought.

[decampos]

The car's been running a little strangely recently, When accelerating the car is jerky and jumping as though it's losing power and constantly feels as though it's going to stall. It idles relatively smoothly though. Also, the dash lights (and headlights) keep flickering. I don't know if that's related.

I've left the car for a week, tried to start it up and the battery is completely dead. (Battery is not more than about 3 months old).

Any idea what the problem(s) could be?

Any pointers very much appreciated.
Ben

 

[Koopman]

Weird electrical problem.

Hi I'm guessing it's an alternator or generator problem. It could also be a loose ground cable.
Good luck.
Koopman

 

[decampos]

Hi I'm guessing it's an alternator or generator problem. It could also be a loose ground cable.
Good luck.
Koopman

Thanks for your reply Koopman. The alternator is fine as far as I can tell (a multimeter comfirmed a healthy 13.6 or so whilst the engine was running). Where is the ground cable?
Thanks
Ben

 

[bill]

The ground wire (a braid actually) is between the engine (top of the bell housing) and the firewall. It usually corrodes significantly after 35+ years. Good idea to clean the connections and replace the braid. I would also run another heavy gauge wire between the block (using one of the oil filter bolts perhaps) and the body. Even better is to connect the alternator casing directly to the body.

 

[rsporsche]

can you still get the braided ground wire? i thought they were NLA ... or just another braided ground from another model?

 

[decampos]

Thanks for your reply bill. I'll locate it and inspect its condition. I've since determined the problem to be a faulty coil. Also, the reason for the dead battery is because I left the rear screen defrost switch on. Sounds crazy, I'll have to double check that.

The ground wire (a braid actually) is between the engine (top of the bell housing) and the firewall. It usually corrodes significantly after 35+ years. Good idea to clean the connections and replace the braid. I would also run another heavy gauge wire between the block (using one of the oil filter bolts perhaps) and the body. Even better is to connect the alternator casing directly to the body.

 

[RogerB]

ECU Ground

The ECU underneath the rear seat in CSis can cause similar problems. Cleaning the mounting/ground screws sometimes helps if this indeed the problem.

 

[jhjacobs]

The rear window defrost should be powered through the load shed relay and thus completely off when the ignition is off. The most likely fast battery drain culprits are the clock, the glove box light, and the trunk light. Have someone close the trunk while you are inside to test this. The glove box is more difficult to test this way.

Here's a link to a wiring diagram. http://www.e9coupe.com/forum/newreply.php?do=newreply&noquote=1&p=89665

I've had stalling/cutout problems resulting from an intermittantly shorting points condenser connector. It was a bear to find. Your coil diagnosis sounds right. Good luck.

 

[pamp]

If this is a CSi.....check and clean all ground connections. I also run a dedicated wire from the battery to the rear of the car to a point beside the ECU. 14 gauge. Trunk mounted battery may be the way to go....I have considered this. Cars are old and weird. Not intuitive to run this extra wire but it works to cure fuel pump issues, rear lighting, etc.

 

[Honolulu]

Braided ground straps are available in several sizes.

I had a bad ground line on my '85 BMW K100RS bike. It would stall at odd moments such as merging onto the freeway. THAT will tighten your sphincter...

Replacement braided straps are available (for my Kbike, anyway) at www.euromotoelectrics.com (no affiliation, und so weiter) see at http://www.euromotoelectrics.com/Battery-Cable-Kit-BMW-K-BCK-5771317-p/bck-5771317.htm

Hint 1: surely braided ground straps are also available at your FLAPS.

Hint 2: You can also put one together with plain old heavy wire and a ring terminal or two.

Hint 3: Low number gage equals thicker cable.

Hint 4: Avoid crimped connections, use soldered connections, with a little dielectric grease when things cool.

 

[sfdon]

Using an ammeter, remove both trunk and glove box bulbs and then replace.

 

[rsporsche]

The rear window defrost should be powered through the load shed relay and thus completely off when the ignition is off. The most likely fast battery drain culprits are the clock, the glove box light, and the trunk light. Have someone close the trunk while you are inside to test this. The glove box is more difficult to test this way.

Here's a link to a wiring diagram. http://www.e9coupe.com/forum/newreply.php?do=newreply&noquote=1&p=89665

I've had stalling/cutout problems resulting from an intermittantly shorting points condenser connector. It was a bear to find. Your coil diagnosis sounds right. Good luck.

just put your smart phone in the trunk or glove box with the video camera feature on - close the trunk or glove box and see if the light stays on.

 

[decampos]

Thanks for the replies guys. Wasn't the coil after all. Even though the points were only about a year old, they were pitted badly enough to cause the rough running. had a new set and installed them, what a difference.

Regarding the rear screen defrost. It really does remain switched on even when the key's not in. The switch itself is located (more unusually) near the window switches if that may make some difference. Anyroad, everything's running great now. Thanks again for the replies.

 

[HB Chris]

Points that go bad that quickly could be caused by lack of the ballast resistor, wrong ballast resistor, unless you have a blue coil which is internally resisted.

 

[decampos]

Thanks for the info. My knowledge is lacking here. I was under the impression that the late cars (mine is within the last 50) don't have ballast resistors. Is it something that's worth installing? (If that's possible). I'm definitely starting to look into one of the many electronic ignition kits.

Points that go bad that quickly could be caused by lack of the ballast resistor, wrong ballast resistor, unless you have a blue coil which is internally resisted.

 

[HB Chris]

Then you must have a blue coil or a resistor wire but not both.

 

[Ed G]

A healthy condenser is also needed to reduce spikes, arcing, and pitting.