"Isolated Ground".

[Bucolic]

I've got a question regarding the electrical system on a CUCV. My son's CUCV wouldn't start, it would turn over but wouldn't fire up. We replaced the fuel filter and all eight glow plugs, recharged the batteries and cleaned the terminals. All of this seemed to fix the problem because it fired right up and ran fine after we did all of that. My question isn't so much as to what was wrong but regards the electrical system and that "Isolated Ground".
While we were attempting to start it, before we changed the glow plugs and fuel filter, I noticed an arc jumping from the washer on the right side motor mount and the frame. Any ideas as to what would cause that? Should there be a ground strap connecting the engine block and frame? I don't know if there is one.

 

[tim292stro]

Yes, there should be at least one ground strap from the block to the frame - otherwise it will ground opportunisticly through mounts, u-joints, mufflers, braided hoses... anything that will carry current.

A key term to remember is: "path of least resistance," you want a good cable at least the same size as the starter positive cable.

You also need a good ground from the battery, if you can bolt the block's ground strap to the same point as the battery to frame point that will give a great return path.

 

[cucvrus]

You can never have to many grounds. Put one from the engine to the frame. I used a 2/0 cable and the frame to the body I used a piece of 4 gauge I had laying around. I just put eyes on each end and bolted them all together with a star washer. Helped a lot of issues.

 

[MarcusOReallyus]

Bucolic, that term, "isolated ground", applies only to the passenger side alternator. You could see that kind of sparking on ANY vehicle, civilian or military, that has inadequate grounding between the engine and the frame & battery.

Everything electrical has to have a return path to the battery. On vehicles, we call that return path the "ground". The glow plugs, the driver's side alternator, the starter motor, and a few other things that hang off the engine have to have a return path to the battery. They do that by connecting to the engine block, which must be connected (somehow) back to the battery.

On these old beasts, the ground strap from the engine to the frame can get corroded, which reduces the ground path available. So, run something that pulls a lot of current (like the starter or glow plugs), and that electricity starts looking for another way to get back to the battery. That's what caused the sparking you see.

Fix it up like mentioned above, and you'll be good to go.


Although, I have to disagree a bit with cucvrus. If you have 50 pounds of 1/0 cable grounding your engine, that's probably too much.

 

[cpf240]

...applies only to the passenger side alternator...

Well... and the GP relay...

 

[MarcusOReallyus]

And the starter relay under the dash....

 

[doghead]

You guys are gonna confuse others.

 

[TGP (IL)]

And the starter relay under the dash....

How is this relay ground isolated?
Doesn't it ground through the harness to the common ground buss?
Tom

 

[doghead]

Yes, but the way it is built(compared to others) it is "ground isolated".

That's why I said you guys are going to confuse others.

Technically, every bulb in your truck is "isolated ground" by design. Just not in use.

Please consider the context of the topic, when you use technical terms.

Basically, all components are either are case/chassis grounded, or isolated ground.

 

[frank8003]

Yes, but the way it is built(compared to others) it is "ground isolated".

Basically, all components are either are case/chassis grounded, or isolated ground.

You guys need some real grounds installed.
Do you want fixed or flexible?
Would you like 100% copper and do you want that with silver hard plating?

 

[MarcusOReallyus]

Yes, but the way it is built(compared to others) it is "ground isolated".

That's why I said you guys are going to confuse others.

Which is why I only mentioned the alternator in the first place. For Bucolic's original question, it's really the only component that matters.

 

[timarr]

There should be 3 grounds at the rear on the passenger intake manifold. 1 to the negative buss bar and 1 to body and other is a wire harness ground.

 

[scottladdy]

There should be 3 grounds at the rear on the passenger intake manifold. 1 to the negative buss bar and 1 to body and other is a wire harness ground.

Correct. These should be colocated on a manifold bolt mounting stud. The body ground is a typical woven ground strap that mounts to the firewall. The other two should be obvious from their descriptions.

There should also be a ground from the front battery negative to the front of the passenger side frame, a small self tapping bolt/star washer combo. From the description of your symptoms the body, frame, and/or negative bus bar grounds are the most likely culprits. However, good practice is to ensure all your grounds are clean and tight.

 

[cucvrus]

I just wanted to show you a picture of the extra ground cable that I attached from the engine to the frame. It was an easy update. I don't know if it was needed but I had the cable and wanted to do something with it. I also ran one from the frame to the body under the cab.

 

[MarcusOReallyus]

Looks good to me!

Did you use any kind of anti-corrosive treatment on the connections?