No crank after motor mounts replaced, 91 318is

[mjimport]

So I just replaced my motor mounts and the car sat for a week (due to temps in the 90s and no a/c)
The car drove to the store a few times but seemed to crank hard each time. I thought it was just from sitting a while.
The last time I went to the store the car left me stranded there, in the parking lot with no crank.
My wife came to give me a jump, still no crank.

My first thought was "I broke a ground when lifting the motor". But then confirmed the strap was still attached and looked ok. Also the strap uses the mount nut so the motor couldn't have put tension on the strap anyway.

I know there are plenty of causes but considering this is likely a result of my recent work, what do you guys think I should check next?
Thanks!

[AndrewBird]

The ground strap should go from the frame rail to the oil pan, not the motor mount. I doubt it's your problem, but it would be worth fixing.

I'd measure your battery voltage first. Should be 12.5v minimum. If you do get it to start, measure it again with the engine running. Should be ~14v.

It sounds like you might have a parasitic draw that is slowly draining the battery.

[mjimport]

Thanks I'll check that out. I just saw some other posts about adding extra grounds, I'll get to that as well.
A few months ago I had a bad radio antenna that was draining the battery but I disconnected that and observed very little draw afterward. I also have a brand new battery and have been driving the car with zero issues up until installing new mounts.

[mjimport]

Pass side strap

Here is the passenger side motor mount strap. I was mistaken, it doesn't use the mount nut but uses the mount bracket with a dedicated stud just for the strap. Either this is the correct ground location for the m42, or someone swapped the mount bracket from some other car..

[mjimport]

The other end attached to the chassis near the inner fender.

[R1dd1ck913]

That is right for a m42 car.

[RCtheRed]

Are the grounds clean and free of any debris? Was there any other time when you left the car sitting and it would not start before?

[mjimport]

I am going to go through all the grounds, but I am having a hard time finding any others besides the one pictured above. I still need to check the underside but I would have thought the driver side would have had a pretty obvious ground at the starter as has been described in other threads.

Since I did not disconnect the strap shown above while lifting the motor for clearance for the new mount, there is a chance that I put tension on it and caused some damage under the plastic coating.
I also noticed the strap coating was cracked, brittle and starting to flake off near the end at the mount bracket. The copper inside is green and getting nasty.

I'll replace that for sure and dig deeper to find other grounds.

Thanks !

[mjimport]

So after some digging it appears there is no ground that runs directly from starter to chassis, but one that is routed in a sleeve as part of a harness, and looks in good shape.

After fiddling with the passenger side motor/chassis strap, I was able to get the car to start several times, although it wasn't very strong.

I'm having some custom cables made up (OEM prices are stupid) and will add an extra one somewhere since I only see one ground between the block and chassis.

[Vanilla Gorilla]

I've also noticed only that one ground strap from the motor mount to the frame rail. The starter had a ground but it was in the harness as you mentioned and part of the 4 connections on the starter.

I'm guessing you check spark plug wires, ignition coils, all the other plugs and sensors etc. since you were moving the motor around, maybe something else came loose?

[mjimport]

Update

It appears the ground strap was weak enough that when I lifted the motor it moved it just enough to lose continuity.
Here is a photo of my new custom ground straps. $20 for all three! :)

[mjimport]

Ok, photo won't upload now, will try later.

[mjimport]

So I replaced the passenger side strap and short alternator strap. I also added an extra strap between the upper bolt on the driver side motor mount at the block, grounded to the chassis via one of the charcoal canister bracket bolts. This doesn't appear to be the best ground as there isn't much bare metal but it's better than only having the one strap. And there really isn't any obvious ground point on the driver side engine bay, aside from drilling a hole and making one.(which I may do at some point)

I also unbolted 3 other ground bolts/nuts around the engine bay and scrubbed them with sand paper.

The car is now holding charge after about two days (so far), starts and runs great again!