Author Topic: Still chasing an electrical issue (Read 3954 times)

willworkfore30s · « **on:** June 26, 2012, 05:59:59 PM »

I've got a 318is that I have been working on. I'm trying to chase down an electrical issue.

I swapped to stock m42 for a lower milage m42 out of a vert. I used the original engine harness and accessories.

The issue seems like a weak connection somewhere. The car is running well with a solid idle but when I drive it, it will intermitently do some crazy stuff. The temp gauge will peg on hot and the engine will have less power. I can floor it and let off the pedal a couple of times and the gauge will go back to normal and it will run fine again.

I am not 100% of this correlation but it seems that if I turn the car off while its in "limp" mode with the temp gauge pegged, when I go to turn it back on I get nothing. The radio and stuff will turn on but the car wont crank, not so much as a starter click. But then I can put the car in gear and roll it dumping the clutch to spin the motor over and then it will crank up. I have had success with this a few times but I am not 100% that it works everytime.

So it seems to me like something is coming disconnected or connected when it shouldn't be and shaking the drive train one way or another seems to giggle it back to the way it should be.

Anyone have an experience with this phenomenon? Any ideas on how to track it down or what it could be?

Daniel Q · « **Reply #1 on:** June 26, 2012, 06:47:19 PM »

I'm also working on my m42 at the moment. Are the wires to the alternator tight and not touching each other?

Geoff · « **Reply #2 on:** June 27, 2012, 05:55:13 AM »

it sounds like a main grounding point may be flakey or missing. make sure there is a solid clean ground between engine and chassis, and between battery and chassis also. make sure ground is solid on the alternator itself as well.
Geoff

lqbanotxano · « **Reply #3 on:** June 27, 2012, 08:27:42 AM »

A bad ground from the alternator to the chassis caused all kinds of problems for me. I finally got a ground strap from a lawn mower (from Carcraft or a tractor place) and had no more problems. The old strap was "corroded" and that was enough to cause problems.

willworkfore30s · « **Reply #4 on:** June 27, 2012, 12:43:36 PM »

You guys are genius'. I got in the car this morning and turned the key....nothing. Got out to check the ground strap as you guys suggested. Motor mount bolt holding the strap on was less than finger tight. Got out a 13 mm wrench and cranked it a couple times. Car cranked right up and its running better than it ever has. I can't believe I didn't notice this earlier. The temp gauge is spot on. The idle is better and it accelerates through the power band much more smoothly. It seems to have more power. It's like a new car.

DRTE30 · « **Reply #5 on:** September 27, 2012, 11:01:06 PM »

That is fricking awesome that you were able to fix your issue with such a simple fix. Not to take over the thread, but to simply move it along, I have a general question:

Let's say for the sake of this hypothetical that all of the grounding points are properly making contact, and the grounding straps are new BUT the grounding strap between the engine block and the alternator looks to be old and in poor condition but tight. Would this one isolated strap cause the symptoms that the OP talked about?

Secondly, it seems that a battery that is not running at optimum performance will create similar symptoms as well. Has anyone had experience with this?

Lastly, if the battery is causing symptoms such as these, what is the threshold of a working battery as opposed to an improperly working/faulty battery?

Geoff · « **Reply #6 on:** September 28, 2012, 08:52:54 AM »

:)rearing its ugly head again, is it? well doc, I'd say yes any underachieving ground strap or wire will cause problems. as already noted by a previous post, the one to the alternator must be good as well. it has rubber bushings, so may not have a good enough ground just by being bolted on. as to a battery, generally speaking, I like to test voltage first, hopefully it will be 12.5 at least, 12.8 would be better. Then test it with car running to see is it being charged. voltage should be 13.2 or a little better. it should not take a huge hit when you turn the headlights on. If a battery seems to have ok volts but wont start the car, it should be load tested. If you dont have a load tester, any polish emporium will have one, go where you got the battery from if you can. then, buy me a beer:D
Geoff

DesktopDave · « **Reply #7 on:** September 28, 2012, 03:57:34 PM »

Batteries are tricky beasts. Best idea is to put it through a few load tests. I've had good luck with used batteries, but I make sure to get them tested at a few auto parts stores before trusting it. Three is usually the charm as many parts counter guys have better things to do.

Ground straps are cheap - IMHO just replace it. I have seen the occasional strap that has corroded internally...less copper makes for more resistance...that makes for less copper...you get the idea. High resistance is also bad for the regulator.

A really good battery will also slightly improve your gas mileage if you can believe it. I've used an Optima Yellow Top with a great deal of success, but they're awfully expensive (~$200). I hate to admit it, but the best battery I ever had was an undersized WalMart unit. It was a freebie - I was cleaning out my FIL's rental unit and rescued it from a frozen puddle. It's now ten years old and running my wife's minivan!