Resistance to ground at different parts of body
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Joined: Jul 2000
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Engine: 5.7L V8
Transmission: 700R4
Resistance to ground at different parts of body
I'm curious to see if anyone has measured the resistance to ground for a working car to get a baseline. I'm having problems with grounding (I think) and I'd like to eliminate different things like battery ground to chassis etc. I haven't done the measurements myself, I figured I'd post this up before work and hopefully there will be replies when I get home. 
I was thinking of using some kind of conductive grease on the ground strap stud to get a better connection, is that a good idea, and if so, are there any recommended types or brands?
I was thinking of using some kind of conductive grease on the ground strap stud to get a better connection, is that a good idea, and if so, are there any recommended types or brands?
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Joined: Jun 2001
Posts: 356
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From: Fort Sask. Alberta
i got a factory strap that goes from the back of the block to the firewall. a 4awg wire going from the block to the strut tower brace. a 4awg that goes from the battery to the seat belt bolt on one sid. and a 0awg wire that goes from the other battery to the other seat belt bolt. both batteries are in the back and the seat belt bolt goes inside the frame. everything seems to work well.
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Joined: Nov 2000
Posts: 440
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From: Cleveland, OH and Flint, MI
Rather than measuring resistances a better bet is to measure voltages. The reason for this is that the resistances are so small that they are hard to measure, but a small resistance can cause a comparatively large change in voltage.
What you can do is connect the black on your voltmeter right to the ground on your battery using a long wire and then check the voltage at various ground points on the body. Do this check with everything turned on and the engine running. The more load you have through the grounds the bigger effect a bad ground is going to have. Ideally you want to see 0.000 volts at all grounds. If you have a bad ground you'll see an "elevated ground" which means the volt meter will read positive voltage at a ground point away from the battery.
It is ok and expected to have elevated grounds in some areas, like the tail lights. It doesnt really hurt anything, and getting rid of it would be expensive. However if you have for example an elevated ecm ground above your main engine ground, it will cause you all sorts of problems because the ecm will see all the sensor values as less than they really are.
Hope this helps
What you can do is connect the black on your voltmeter right to the ground on your battery using a long wire and then check the voltage at various ground points on the body. Do this check with everything turned on and the engine running. The more load you have through the grounds the bigger effect a bad ground is going to have. Ideally you want to see 0.000 volts at all grounds. If you have a bad ground you'll see an "elevated ground" which means the volt meter will read positive voltage at a ground point away from the battery.
It is ok and expected to have elevated grounds in some areas, like the tail lights. It doesnt really hurt anything, and getting rid of it would be expensive. However if you have for example an elevated ecm ground above your main engine ground, it will cause you all sorts of problems because the ecm will see all the sensor values as less than they really are.
Hope this helps
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