Effects of poor grounds?

[Joe62Tampa]

This is a different type of issue I've experienced on the '88 Scorpio aside from the "Dr. Jeckyl, rough running 2.9", the following link:

viewtopic.php?t=39001

But, perhaps it's related. The car seemed to have run better yesterday after it warmed up and got over its initial "coughing" spells. However, I was able to cause the engine to sputter, cough, have a difficult time running whenever I placed an electrical load onto the electrical system. For example, turning on the parking lights, then the head lights would cause the car to begin misbehaving. The worst one is enabling the rear defroster. Could a missing, or a bad ground cause the car to run so poorly? Of course, there could simply be a ground that is missing (from the last time a shop worked on it, or that I may have).

I have the breakout box that can be placed between the wiring harness and the computer. It'd be interesting to run some of the tests using outlined test points to check for expected vs actual values.

Thoughts?
What'd be some signs of one or more bad or poor grounds at the whole car level?

[brokencase]

That is strange.

High current load causes engine to run bad.

I'm going to say there is something wrong with the alternator. Blown diodes or something like that. Possibly a bad POSITIVE connection from alternator to battery.

The reason I say that is your indication that turning on the rear defroster is the the worst.
Under this case the current draw is high which would mean the alternator regulator is "kicking in" to accommodate the load.
But if partial diode failure in the alternator, then it could mean your getting AC on the supply, which would reek havoc on the EECIV.
If a bad positive connection from alternator to battery then you may see a large drop in DC voltage when you turn on the defroster. Low system voltage would also be bad for the EECIV.

Test by placing a Digital multimeter in AC mode and turn on the rear defroster and observe if there is an AC voltage appearing on the cigarette lighter socket or on the battery terminals. Also check DC voltage with the defroster on.

If the case of a bad ground then I would think things would be bad all the time. Also what ground would go bad? I guess you might want to check if there is a proper grounding strap between engine and chassis. Although that would be a long shot. Either never put back in after an engine pull or rotted away.

Also check the connections on the positive terminal of the battery. There could be some corrosion causing a faulty connection on one of those wires.

[Ed Lijewski]

Wouldn't a defective VRegulator also result in these symptoms?

YMMV

[brokencase]

Wouldn't a defective VRegulator also result in these symptoms?

YMMV

Like I said "something wrong with the alternator"...