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Ground Loop

2K views 5 replies 3 participants last post by  astro355 
#1 ·
I've been installing a Nordsdok Digital Gauge Panel and it all went well untill I hooked up the speedo. This is installed in a 1989 Cargo with a 1989 TBI 350 V8 hooked up to a 700R4 tranny that has a VSS.
I've been talking to tech support and they are asking to make sure I don't have more than one "Ground Loop" in my electrical system. As far as I know, the way I have the ground hooked up is: the battery ground is tied to a bolt on the body at the radiator support, then goes from there to a bolt on the intake manifold.

The problem is that sometimes while being at a stop, the speedo starts to show speed numbers and then goes back to cero. The tech guy says it's more then likely a grounding problem. That there should be only one "Ground Loop".
The biggest problem is: I DID THE MOTOR SWAP!! :whack: so of course I don't know any specs on how it was done!! to much :cheers: if you know what I mean.

Any advise on what I'm missing?
 
#3 ·
That doesn't sound like a ground problem to me.
I think it might be picking up electrical noise or ignition (spark plug) noise that is being radiated into the speed sensor leads or DRAC output.

I have seen instances where reving the engine in an Astro/Safair with the factory digital dash will cause the speedometer to read a few miles per hour and go back to zero at idle.

The speedo counts pulses and having a issue with a bad or poor ground, I thnink, would cause the gauge to either not work, change brightness, or read wrong at all speeds. But you might also be fighting an inherent design problem in the vehicle wiring since I have seen the factory digital do the same thing.

There is no easy solution since the VSS in the trans feeds a module (DRAC, Digital Ratio Adapter) in the dash that cleans up and divides the output of the VSS into pulses that go to the ECM, cruise control, and speedometer. The only solution I could suggest would be to try a replacement DRAC module or change the VSS sensor. And probably none of them will positivley cure it.
 
#4 ·
'cudapaul said:
I have seen instances where reving the engine in an Astro/Safair with the factory digital dash will cause the speedometer to read a few miles per hour and go back to zero at idle.
And that is because there is not "enough" of a ground to cover the system.
'cudapaul said:
The speedo counts pulses and having a issue with a bad or poor ground, I thnink, would cause the gauge to either not work, change brightness, or read wrong at all speeds. But you might also be fighting an inherent design problem in the vehicle wiring since I have seen the factory digital do the same thing.

There is no easy solution since the VSS in the trans feeds a module (DRAC, Digital Ratio Adapter) in the dash that cleans up and divides the output of the VSS into pulses that go to the ECM, cruise control, and speedometer. The only solution I could suggest would be to try a replacement DRAC module or change the VSS sensor. And probably none of them will positivley cure it.
If you completely remove the ground, the gauge will spike, not stop working. I would stick with the tech's advise here.
 
#5 ·
yeah, I need to make sure my ground loop is sound. My ground cable goes from the battery to the body and from there to the engine intake manifold. I'm gonna make sure I go from the battery onto the engine block and from there to the chassis and from there to the body.

The motor mounts are isolated by the rubber bushing, correct?

Thanks for the help guys.
 
#6 ·
You don't have to worry about that. There are several places were the engine wiring harness grounds to the block but you need the big ground cable going from the battery to the block. You really shouldn't be able to start your van without that ground.
 
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