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Fuel sending unit
Posted: Sun May 10, 2009 3:13 pm
by nanuke
I installed a new unit from John at Midwest and noticed that when the tank was full it only read 1/2. I removed the unit and checked the float with the ignition on and it read perfect. I noticed while reinstalling the scews that once the screws got tight the reading suddenly went down to 1/2 again. Is there a grounding issue with the screws and the tank? I tried to use a rubber washer between the screws and the snding unit and it seemed to help but not as good as before screws were tightened.
Posted: Mon May 11, 2009 5:55 am
by Cal_Gary
Ir's likely a bad ground-I have the same symptoms with mine but haven't had time to check it thoroughly.
Gary
Posted: Mon May 11, 2009 9:06 am
by MSeriesRebuild
It's best to run a ground wire back to the frame from a screw that holds the unit in the tank. The unit must be grounded. If this doesn't correct the issue, most likely the sending unit is flawed. We have taken a number of new ones out of the box that were bad. I don't know where John sources his from, but we've had a hard time finding good ones lately.
Posted: Wed May 13, 2009 12:12 pm
by knattrass
Charles - we built a dedicated ground wire into our rear harness which daisy chains its way to all the rear lamps, fuel tank, etc. Same for the front. Our new sender reads 1/4 to 1/2 in park and will jump all over the map when driving. We figured the new sender we got was bad - looks like you have confirmed that.
Posted: Wed May 13, 2009 12:12 pm
by knattrass
Charles - we built a dedicated ground wire into our rear harness which daisy chains its way to all the rear lamps, fuel tank, etc. Same for the front. Our new sender reads 1/4 to 1/2 in park and will jump all over the map when driving. We figured the new sender we got was bad - looks like you have confirmed that.
Posted: Wed May 13, 2009 2:47 pm
by MSeriesRebuild
knattrass wrote:Charles - we built a dedicated ground wire into our rear harness which daisy chains its way to all the rear lamps, fuel tank, etc. Same for the front. Our new sender reads 1/4 to 1/2 in park and will jump all over the map when driving. We figured the new sender we got was bad - looks like you have confirmed that.
That's a great way to do the ground. It isn't unusual for the needle to fluctuate when driving because of no fore-aft baffling in the tank. If it always reads 1/4-1/2 when idle, even when the tank is full, there is an issue somewhere, most likely the sender.