Hello fellow Brickers,

Here's a puzzler: With the headlights on, turning the high-beams OFF causes the engine to briefly cut out!

When driving, or in park revving the engine, it doesn't cause the engine to stall out (seems to cut out for a split second).

But when idling in park (~600 RPMs), it causes it to stall completely!

ANY THOUGHTS ARE GREATLY APPRECIATED...

 

You have an earthing problem. Check the many earthing points in the car and sandpapper clean them up and spray oil on them.

 

I suspected as much.

Are there any non-obvious earthing (grounding to us Yanks) points on the brick that I should know about?

 

what year/model car? 740/940's have primary grounds at 1) battery cable on frame rail 2) inside of fender near right headlight 3) inside of fender near left headlight 4) inside of firewall behind dashboard. there's a few more in back, that aren't associated with the engine or headlights. 240's have them in similar but somewhat different places.

 

Thanks Pierce, it's a 1991 740 wagon.

 

oh, and the main engine ground is on the front bottom of the block, just above the starboard front corner of the oil pan, this goes directly to the battery negative.

there's also some other secondary grounds to be complete... the tank fuel pump and miscellaneous stuff is grounded in the trunk near the access plate on sedans, and near the left tail light on wagons. on wagons, each taillight has a ground right next to it. power seats are grounded to the metal frame that supports the shifter. the abs control unit, speedo and cruise control control unit are grounded near the drivers door lower hinge.

 

Check, check, check and check.

Other than removing the ground bolts, cleaning them, and reinserting, should I do anything else (e.g. dab of dielectric tune up grease, spray after insertion with lithium grease, etc.)?

TIA

Dave

 

Fixed it!

Turned out there was a bus with three tabs on the inner fender behind the right front headlight.

The center tab (it went into a harness, so I couldn't easily trace it) was corroded to the point it was broken off.

Stripped some bare wire, cleaned the contact, re-attached the wire, plugged it in... Done!

Going to engage in a little prophylactic maintenance and go through the rest of the contacts over the next week.

Thanks everybody!!!

 

check the ground terminals on the other side, too. i listed above what goes where...

 

I'm sorry that I've been offline for a while... but I just wanted to comment that about a year ago, I had the same problem on the '89 740T I was running around in, and the remedy was the same. Well, I think mine was on the left side (I get those things confused rather often...), but otherwise the same. Like you, my brother and I went around and cleaned all the grounds... and it resolved the problem.

 

Another ground "bus" is on the left inner fender.
I took it off, cleaned all the connections and connectors, sanded under the bus, cleaned the mounting screw, and every thingstarted working.

One other symptom: With the high headlights on, turning on the left turn signal dimmed the headlights with every blink.