Strange electrical problems - Fixed
 

OK, something strange developed in the last couple of days.
Engine temp gauge jumps erratically and intermittently.
At the same time, the headlights and dash lights tend to flicker.
Once in a while during this phenomenon the engine hesitates.
Sometimes the glow plug lamp will also flicker.

I'm thinking this could be a ground issue on the instrument cluster, or maybe a voltage regulator issue. Has anyone else experienced something like this, or have any input.

An electrical schematic would also be helpful, if someone has one.

1980 300SD W116. - 360,000 miles and still going.

Check the battery cables.

Grounded!
 

An electrical ground issue would be the first thing I would look for. One that often gets overlooked is the heavy wire under the car that connects the engine to the chassis. It should be clean and tight.

There are also "clusters" of brown (ground) wires connected to body studs here and there under the hood, behind the instrument cluster, and probably other places like the trunk. Check each one as you find it, make sure the nut securing the wires is tight and that none of the wires have been broken.

Electrical problems should not cause a diesel to miss or hesitate. If not psychosomatic, that is most likely some kind of fuel problem -- an air leak in a fuel line, for example.

Jeremy

Thanks for the feedback
 

Thanks for the quick responses. If it is warm enough today, I will look these items over during my lunch break.
It's my daily driver and making me kind of nervous at this point.

Thanks again.

Fixed, for now.
 

The problem - the alternator had begun to shake loose. The two bolts on top were no longer tight. The bolt on bottom had vibrated for a long enough period to waller out the bolt hole in the alternator.
Since the alternator is grounded through its case, to the engine block through the bracket, It was losing ground.
So, as a temporary fix, and to prove that this was the problem, I used a #8 wire off the back side of the alternator to the chassis ground (where the battery connects to the chassis).

The problems seem to be gone. However, I need to get a new alternator, bracket, and tensioning bolt. Anybody got an extra lying around?

I will see how it acts on the way home tonight.

Definitely fixed
 

The ground wire definitely solved the electrical problems.
I haven't had any hesitation since then either.
I realize that the diesel will run without the battery, but I wonder if it was just in my mind that it was hesitating, or if something electrical really could have caused hesitation.
I guess it doesn't really matter at this point, it's running now.

I need to get an alternator, alt. bracket and bolts to fix it right.