OK, the car got a 90 E300 alternator upgrade, and I STILL could not get the car to charge the battery...

tested the alternator, good.
car started fine, but would NOT maintain charging.
I'd start the car, I'd get 14.1 volts, then it would slowly drop down to 12.2... TOTALLY miffed me.

I didn't think it could be the ground strap because the car started fine.
I was wrong.
the ground strap was loose, and pitted. I took everything apart, cleaned and filed smooth the strap, and the bolt, and went to tighten everything back down only to find that the threads are gone in the bellhousing... CRAP! the bolt would not pull tight. (is the bolt supposed to poke through the motor plate? I think it's the wrong bolt.)
anyway, I drove to the parts store, and picked up a 40" ground strap, and removed the ground cable from the body connection at the battery, and cleaned it all down to the metal, and put the new strap in there, then routed it through the bushing in the heatshield, and routed it over to the intake manifold. I put it under a shield bolt to the manifold.
INSTANT starter action, and the alternator now puts out 14.3volts with EVERYTHING on.
I bet this will fix the temp gauge problem I had too...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Always nice when you can fix a problem that was hiding right in front of your face Those can be the hardest to solve sometimes.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

I am saving this thread.
People always seem skeptical when you say there Alternator issues might be caused by the Wiring and the Grounds.

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84 300D, 82 Volvo 244Gl Diesel

Yup. Totally fixed both charging AND it fixed the temp issue!!! my temperature gauge days rock solid on 80 now

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I had a student that kept missing classes due to dead batteries in the car (a mid 2000's ford focus) his uncle gave him to drive. They put 2 new alternators and a battery in it, and still had the same problems. He was at the mercy of his "mechanic" uncle to get the car fixed, so I took a look at it with him. There were lots of "rigged" items that jumped out as soon as he lifted the hood indicating his uncle's talents. Wirenuts under the hood of a car is never a good sign! Anyway, I quickly discovered resistance between the engine block and negative terminal of the battery and told him he had a cable issue of some sort. He took the car back to his uncle who said it was definitely not that, and made the guy buy a used OEM alternator at the junkyard to try. Still had same problem so his uncle gave up. He could make it to school if he charged it overnight, and the weather was clear. If he needed the wipers and headlights he was screwed...

Student brought it back to me to look at, and I noticed a spark at the back of the engine when he went to start it. Sure enough there was a burned spot where a couple of the accessory brackets bolted together - and the ground cable was bolted to the bracket that then bolted to another bolted to the head. Looked like a royal pain to get the brackets out, and seeing as how it was his uncle's car who knew it all I quickly worked out a solution. Did I mention this student is in a welding program I teach at a community college? Had him reach back in there with a 6010 electrode and nuke the place where the 2 brackets mated up. Instantly he had perfect charge from the alternator and no more dead batteries. I hope his uncle doesn't need to take those brackets apart....

classic!

I've never used wirenuts to fix an electrical problem on a car that was not trailer lights... even though I carry most sizes in my vehicle... (I'm an HVAC contractor...) unless we're talking about stupid trailer lights...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

If I am troubleshooting weird issues (such as lights half lit, or relays that pull in but won't release) in a control panel the first thing I always check is the common side of the circuit. 99% of the time that is where the problem is.

When I redid the battery pan on my 240D, I cleaned the ground cable connections, that cleared up the jumpy behavior in the fuel and temp gauges.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech