How is the starter grounded?

[Jay87]

Hey guys,

Trying to diagnose a problem where my starter will not engage or turn over. Car is an '87 is coupe with a three-terminal solenoid.

I have battery voltage at Terminal 30 (from junction block). I will check to see if I get 12v from the small wire (terminal 50) as soon as I can get a second pair of hands. The braided wiring strap from the solenoid terminal opposite the line from the junction block is in place, though it looks old.

What I do not know how to check is whether or not the starter is properly grounded. I don't see an obvious grounding terminal anywhere. How can I check to see if the starter and solenoid are properly grounded?

[StereoInstaller1]

The strap is the ground.

[Jay87]

Thanks for the quick reply. I do get battery voltage at terminal 50 with the ignition to start. If I pull the line from the junction block and touch it to the terminal with the connecting strap, I can hear the main relay cycle on. If this is the ground, why did this happen?

And, since I have 12v at terminal 30 and 50, does this confirm that my starter must be replaced?

[StereoInstaller1]

The relay click you hear is the unloader relay, the starter has nothing to do with the main relay. That is run by the green/black wire: it stays grounded until the starter cranks the motor over, then it is 12V.

[StereoInstaller1]

also, you wanna test your starter from the diagnostic port: look up your schematic on unofficial BMW, search for "resetting inspection light".

[Jay87]

I didn't even think about the diagnostic port... oh well. Starter is out now, gonna go find a replacement and give it a shot. I'm thinking it should be fine since I have 12v at terminal 30 and then at terminal 50 with the ingition to 'start'.

Will post back!

[Jay87]

Okay, the starter runs fine on the bench at autozone.

Let me get this straight - the solenoid grounds to the motor body via the strap, which grounds to the chassis only by virtue of its mounting face on the flywheel?

If this is true, I will clean all surfaces with wire brushes and consider adding another ground where the strap meets the solenoid. Sound legit?

[StereoInstaller1]

Okay, the starter runs fine on the bench at autozone.

Let me get this straight - the solenoid grounds to the motor body via the strap, which grounds to the chassis only by virtue of its mounting face on the flywheel?

If this is true, I will clean all surfaces with wire brushes and consider adding another ground where the strap meets the solenoid. Sound legit?

No, that sounds silly. BMW did a fine job of grounding the block, don't fuck with it, just a waste of time and materials.

Starter grounds to block, block grounds to body, body grounds to battery. No issues if all is in OK or better shape.

[Jay87]

Well, you get to laugh at me now then. I grounded it with a 12 gage wire and tried to start the car. I burned the hell out of the wire, and got the solenoid to click, but the starter motor didnt turn.

I used a wire brush to clean the surface between the flywheel housing and the starter flange, and used copper paste when putting it all back together. Is there a certain grounding strap or straps that I need to test, and how can I test them?

The only one I have looked at is the ground between the oil pan and chassis, which looks old, but I can measure battery voltage when using the pan side of the strap as a grounding point.

Whats next? Sure would be nice if this car started.

[Jay87]

Looking at the bentley manual, I just realized that my starter bracket is missing. The starter is held on to the engine only by the flywheel housing. It occurs to me that if this became loose and fell off, that might have been the origin of my trouble if this bracket is responsible for grounding the starter.

Though when the car originally failed to start, it was sitting in a parking spot where I had previously started it. I noticed no pieces lying on the ground. Also, the posts on the rear of the motor dont look as though they've had nuts mounted to them for some time. Still, I figured this was worth mentioning.

[Jay87]

So how do I actually test to see if the starter is grounding? I assume it isnt, obviously... how should I go about troubleshooting it?

[StereoInstaller1]

Dude, the starter is bolted to a huge hunk of metal, which is grounded with a huge strap.

The damn thing IS grounded!

[Jay87]

Then this doesn't make any sense. Once again, when starter is keyed, I get 12.6 volts at terminals 30 and 50.

Starter operates fine on a bench rig at Autozone where the ground cable is clamped on one of the ears on the mounting flange. I dont want to just throw parts at this, and it seems like a new starter is not needed.

Why the heck won't this run when I turn the key?!?!?

Car push starts fine, everything else is good. Why wont the starter run?

[StereoInstaller1]

Well, there are other possible causes. Have you disconnected the black/yellow and hit the key? You might also have the main 12V going to the wrong terminal.

Did you look at the ETM?

[Jay87]

I've been through the Bentley's troubleshooting section about the starting system, with no help there. I have it hooked up just as they show, which is the same way it was hooked up when I tore it apart today... this just doesn't make any sense... the functions seem so simple, and I feel like I'm meeting all the criteria.

Thanks for all the help... any other ideas?