Battery Ground Problem

RogerB

RogerB

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My coupe recently stared turning over slow when starting. Then it would not turn a full round but just "bump" . The battery was six years old, so I suspected it. I took it to NAPA and has it tested. It tested good. Brought it home and reinstalled with same result. I charged it to 100% with no change, so I bought and installed a new battery and still no change. I had an idea and connected the negative pole to a jumper cable and the other end to the block. Bingo! It turned over fast and started as it should. I had a new pretty copper ground cable I had purchased off of here a while back and installed it. I cleaned the factor mounting area on the fender although there was no sign of corrosion and installed it. Still no turn over! I checked the ground strap on the fire wall as best as I could loosen and retightened it. Same result: no turn over.

I don't want to add another ground cable from the battery directly to the engine, so what am I missing here?
I have owned many coupes, and the factory ground on the fender has never been a problem. Thanks for any suggestions. RB
 
Well, either your battery - body, or your body - engine ground isn't working. I would guess it's the body - engine strap, since you have already changed the battery - body strap and since the body - engine is the harder of the two to access (in my experience, components that are easy to get at never fail).
 
RogerB said:
Just the purist in me I guess? };>)
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Never had that problem. If it doesn't work, I fix it. The battery basically has one purpose, and that is to start the engine. Once the engine is running, all current returns to the case of the alternator, which is grounded to the block.
 
Paint, and rust could be a great problem for the ground area for the negative cable. In some cases the cable looks good on the outside upon inspection, but on the inside could have cracks in it due to old age and functioning under different temperature ranges. I would recommend that you replace the cable completely.
 
Bill 74 3.0 CS said:
Paint, and rust could be a great problem for the ground area for the negative cable. In some cases the cable looks good on the outside upon inspection, but on the inside could have cracks in it due to old age and functioning under different temperature ranges. I would recommend that you replace the cable completely.
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As said above, I have already replaced the top cable. I have a pretty new lower cable to replace when I figure out how to replace it. I haven't looked at it from the bottom yet. Anyone have experience replacing it with the engine in place? Thanks! RB
 
Assuming the lower cable is the battery to alternator cable, you simply unbolt it form the starter, loosen the connection on the battery and pull it out.

I would reiterate the body to block ground suggestion. Only the purist of purists would notice this, and it helps a lot.
 
Ohmess said:
Assuming the lower cable is the battery to alternator cable, you simply unbolt it form the starter, loosen the connection on the battery and pull it out.

I would reiterate the body to block ground suggestion. Only the purist of purists would notice this, and it helps a lot.
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I am referring to the firewall to engine cable I want to replace.
 
The best engineering practice would be directly from the battery negative terminal to the block. Fewer connections to go bad, less paint on the block, etc.
 
Mike Goble said:
The best engineering practice would be directly from the battery negative terminal to the block. Fewer connections to go bad, less paint on the block, etc.
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I am fully aware of that. Just trying to keep it as BMW designed it. Not trying to be a smartass, but I have a fair understanding of batteries in that I was an electrician in the U. S. Navy Submarine Service and maintained two sets of main propulsion batteries on three different diesel electric submarines which consisted of 252 cells each being approximately 1' x 1' x 6'. If this was one of my previously owned coupes, I would "just fix it", and I may have to end up doing that if other efforts are in vain.
 
Roger, I'm not that good with electrics but did you check the ground strap from the rear of the engine to the area just above the transmission tunnel. You seem to have isolated the problem so it should be some trial and error from here. I have also experienced some grounding issues from the area around the coil. Please let us know what you find.
 
What you bolt on today to get your car running can be unbolted tomorrow after you have figured things out. Not to be a smartass, but this seems to be an unusual thread to be started by an electrician.
 
Peter Coomaraswamy said:
Roger, I'm not that good with electrics but did you check the ground strap from the rear of the engine to the area just above the transmission tunnel. You seem to have isolated the problem so it should be some trial and error from here. I have also experienced some grounding issues from the area around the coil. Please let us know what you find.
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Peter :

I'm pretty sure the problem lies in the ground strap you refer to. I'm just trying to find the easiest way to replace it with the new one I have.
 
Mike Goble said:
What you bolt on today to get your car running can be unbolted tomorrow after you have figured things out. Not to be a smartass, but this seems to be an unusual thread to be started by an electrician.
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Don't even have to bolt it on. Placing one end of a length of electrical wire underneath the negative post connector and laying the other end on anything connected to the block provides sufficient ground to make the car start normally. So, this leads me back to believing it is the firewall to engine grounding strap. Just trying to figure out the easiest way to access the bolts/screws to replace the strap. The electrical knowledge is not the problem.Mechanical access is the holdup at present. Be safe. RB
 
Mike Goble said:
Don't worry, I'm well grounded...
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Mike - hoping to also be well grounded, in addition to replacing the missing tranny to firewall strap, I added an alternator to block strap, and a ground cable from the alternator ground site to the battery ground location on the fender. Then I added a ground strap from the block to the subframe around the motor mounts.
 
Roger, not sure of the access with the CSL, but on my carbureted CS it's easy to get to with the air filter off. I don't think working from underneath will help at all so possibly put some heavy padding on the fender and lie down on top there so you can access it without destroying your back, the paint-or both. I believe the sheet metal screw is a 10mm at the tunnel and then there is the engine side??

Good luck!
 
Repaired it my way and from the bottom! Put it on my lift and noticed a very slight bit of movement on the ground strap to bell housing end. Got my ratchet and long extension and turned the bolt about 1/16 of a turn. Got out and turned the key to hear the beautiful music of the 3.0! };>) Thanks for all of the responses and have a great weekend. I know mine will be much better with this problem solved! RB
 
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