Oil pressure gauge issue
 

My buddy's Four Winns Liberator is doing something strange. With the key off, when he turns the blower on it pegs his oil pressure gauge. The bilge pump, lights, etc also move the gauge but not as much.

Any ideas?

Check the Grounds under the dash, and at the engine block, from the main harness. Should be a 10 gauge wire going to the engine block, or bellhousing bolt, etc. Then, under the dash, check all the ground connections. A weak or bad ground for the accessories, will try to find ground thru the gauge.

Thanks MT. I was thinking it was a ground issue but I thought it was weird that most accessories affected it, and not just one. Going over there tomorrow so we'll check grounds thoroughly.

More confused now! We checked all grounds and they seemed good. Then the gauge started pegging at 80 as soon as you turned the key. So, we started looking at the gauge and sending unit.

We hooked a brand new gauge to the sending unit and used jumper wires to power it off the battery. Gauge still pegged which eliminated any grounds in the dash. Grabbed the sending unit he just replaced and hooked it to the new gauge. That one also pegged. Grabbed the original sending unit and that one doesn't peg.

I took the two that pegged home with me and tested them with an ohm meter. With no pressure one read 1 ohm and the other 4. So, that means almost 100% continuity. Here's the weird part. When I applied 60lbs of pressure one came UP to 60 and one 90(I'm going off memory). When you ground a sending unit(0 ohms) it pegs the gauge, so it seems these two units are backwards?

I grabbed one of my spares that I know is good and at 0 pressure it read 160 ohms, at 60 lbs of pressure it read 50 ohms. Which makes sense, lower ohms higher pressure reading. Which is why the gauge pegs when you ground it(0 ohms).

So, is it possible something is wrong with his gauge and it's feeding voltage to the sending unit and frying them?

what brand of gauges? what sending units? some of the newer sending units have 2 terminals and one is marked G and most think its Ground when in fact it means gauge .....

I chased the same thing finally ran a new ground from the gages to the engine, also I was told if you put sealer or Teflon tape on the oil pressure gage it will cause the same thing. leave some room on the sensor so it grounds

VDO gauge and one sending unit is also VDO. Both only have one terminal.

We grounded the gauge to the engine and ran the positive lead directly to the battery using jumper wires so we eliminated that. I just don't understand why two of the units seem to work in reverse.