Electrical Gremlins - '85 280SL Euro

[gswartzfager]

Okay. Chuck said to ask away, so here goes. This one has me and my mechanic stumped. Motor rebuilt. Now, starter will spin -- sometimes. Sometimes not. Like dead spots in the ignition switch. Tach bounces from 2,000 up to about 4,000, but only when car is cold. Usually gets settled down and all is well. Oh, and the horn won't work. Don't know if they are all related or separate. Everything else electrical is working just fine.

Sounds like a bad ground, right? I have looked and tightened up everything that even looks remotely like a ground. Under the car, under the hood, under the dash, you name it. Took the battery out. Pulled negative cable, cleaned, scaped and so on. Cleaned all the bus connections under washer resevoir. Two new ignitions switches, nothing. New starter when motor rebuilt. New one replaced under warranty just to make sure. Neutral safety switch replaced. Linkage is fine and all. OVP had the fuse blown. Replaced the fuse. Nada. I cannot bend enough to to it to test it while in the car, so that could be an issue. Horn has current at the wheel, but won't get through to the horns, which have been tested and are fin. Could the OVP be the source of at least some of these woes? I am really thinking that they are not related, but who knows, maybe they are.

I got a steak dinner, cold beer, or whatever you choose to spurge with to whoever can figure this one out. I hate electrical gremlins. They are the worst.

Thanks for any input.

Glenn
I am not thinking

[350SL4spd]

That does sound like a bad ground. Easy to say from here, I know .

My father spent more than 30yrs with a similar problem on his old Jeep FC. After years of going under the truck with a screwdriver to jump the connections on the solenoid, he ended up installing a jumper wire to a switch in the dash for the days it was being a punk. He never did find the source...

I'm not sure why I went off on that anecdote... lol. This problem is distinctly ringing a bell in the back of my mind but I can't get it into focus. I'll chime back in if I remember...

I'm sure you'll find the source one way or another, and make sure you let us all know what was the cause.

Good Luck!

[Gurunutkins]

just a thought but you say the motor is rebuilt. did you replace or reconnect the big grounding strap at the bottom of the bell housing to the chassis otherwise you could be trying to earth the starter through the small gauge wires that run to the engine. probably you have done it but worth checking. it probably wont help width the horn problem though
cheers
Barri

[t walgamuth]

Originally Posted by Gurunutkins

just a thought but you say the motor is rebuilt. did you replace or reconnect the big grounding strap at the bottom of the bell housing to the chassis otherwise you could be trying to earth the starter through the small gauge wires that run to the engine. probably you have done it but worth checking. it probably wont help width the horn problem though
cheers
Barri

x2.

Also sometimes an extra ground strap from a starter bolt to the negative on the battery will help.

Tom W

[gswartzfager]

Thanks for the help so far. The grounding strap from the bellhousing is definitely on there good and tight and corrosion-free. I had not thought about adding and extra grounding strap directly the to starter. That might be my next move. I am definitely thinking the horn is not related. I recall having an issue with it before the banishment of the poor car for her rebuild, so I don't think it is related. The tach, for this morning at least, cooperated after I replaced the fuse in the OVP. I will have to wait and see if it continues to behave.

Glenn

[GSMITH]

You might have answered your own question.
"Like dead spots in the ignition switch."
Does this mean you get to take yourself out for Steak and Beer?
Next time it does not work wiggle the key around in the Start position.
It is a $30 part. I am talking about the switch not the lock tumbler.

Mine gave me problems with the AC interior fan once in a while. Fan would stop out of the blue and key wiggle fixed it temporaraly. Once replaced no more problems with the fan at least. Yours might be giving you intermintent start and no Horn.

Scroll half way through this post to see how the switch is connected to the back of the lock assembly. http://www.dieselgiant.com/repairignitionlock.htm
Unfortunatly I found this post after I had already removed the assembly.

You already seemed to check the ground out pretty well.
I chased the same starter symtom in a Jag XJS for a year before I found the battery to chassis conection needed cleaning on the chassis end in the trunk.
The fuse on the OVP probrobly got blown by a jump start.
You already found how it causes a problem in the Tach but I never heard of it going away once things warmed up.

[nobby]

Originally Posted by GSMITH

You might have answered your own question.
"Like dead spots in the ignition switch."
Does this mean you get to take yourself out for Steak and Beer?

I think he said he has replaced it twice.

Any cluster problems seemed to be solved adding a ground wire from the cluster to the chassis under the dash.

[gswartzfager]

Okay. Brand new ignition switch. Still screwy starter. Brand new fuel pump relay. Tach is still jumping. But new issue. Sometimes when car is cold and I go, it will die. Losing spark or fuel, don't know which because it dies for about 2 seconds, catches back up and is then fine. Once warmed up no doesn't do it. Tach is still jumping all over the place, usually but not always when cold, so it could be that it is so high the rev limiter kicks in for a second and causes the stumble.

Okay, now for a strange theory. The main grounds are in the passenger foot compartment against the outside firewall. All of them are good and tight clean on the inside. Now, here goes. My former law partner hit the right fender. Had it fixed and painted. Looks great, but if the fender was off to be replaced, could it be something on the otherside of the main grounds did not get replaced properly or messed up the ground? Strange theory, but it is all I got at this point. The starter issue is between the ignition switch and the starter because when it is acting quirky, I can jump a wire directly to the starter and the battery and it spins just like it should. All the wires between the switch and going outside seem to be good. I still think it is a ground issue. Gotta be. So I am completely crazy with the idea of the fender damage and repair causing this? Did not do it before, but had the fender and the motor rebuilt at the same time.

Sorry for the book.

Glenn

[350SL4spd]

I'd say that that was a pretty out there theory, but I've had a hell of a lot weirder things happen to me while trying to find the source of my torment.

I guess the only obvious trial would be to pull all the grounds off that side and bolt them to a wire directly to the (-) on the battery? If that fixed it, I guess you'd know. It's a long shot, but its not too difficult to try.

You might also (as long as we're talking long shots) jumper the important wires off the ignition switch (to where they're supposed to go) to rule out a short in any of them. That is definitely possibly a culprit .

Good Luck!

[gswartzfager]

Okay. Work has been completely overwhelming lately, but finally I have gotten two of the issues resolved. The horn was a pinched wire in the steering column from when I replaced the universal joint that connects to the steering box. Fixed that. The bouncing tach was not so easy. New fuel pump relay did not fix it. I was afraid it was in the distributor as my mechanic suggested. Nope. Before I busted into the distributor, I replaced the coil and ignition control box with an aftermarket one made by Heuco, as that seemed more logical. That fixed that problem. Now if I can only remedy the starter problem, I am good to go. I have not had a chance to run a ground straight to the starter yet, so perhaps that will fix that. I any event, serveral different non-related problems. I hope this helps someone with a similar tach problem in the future.

[Roncallo]

It sounds to me like your biggest problem is you are diagnosing by process of elimination rather than using a voltmeter. That is a very expensive way to work.

Step 1) Place + volt meter on S terminal of starter - terminal on ground. Rotate key to start is there 12 volts yes/no?

Yes - trouble shoot starter or cables to starter.

No - go to next connector up the ignition stream and repeat step 1.

[350SL4spd]

Ron, How you find time to diagnose other people's issues with that project you're running right now I'll never know...

Your cool head & knowledge are needed & appreciated.