Another Oil Pressure Question

[scape]

I read through the threads and didn't see this issue.

85 with 350. Have the dual oil pressure sensors.

I swapped the motor/trans/body from a 2500 frame to a SWB 1500 frame. Oil pressure gauge worked prior. We fired up the motor after the swap and the gauge is all over the place. It jumps from 20 to 70 and back. It acts like a ground issue but not sure what could have changed there. Any ideas?

 

[Bextreme04]

I read through the threads and didn't see this issue.

85 with 350. Have the dual oil pressure sensors.

I swapped the motor/trans/body from a 2500 frame to a SWB 1500 frame. Oil pressure gauge worked prior. We fired up the motor after the swap and the gauge is all over the place. It jumps from 20 to 70 and back. It acts like a ground issue but not sure what could have changed there. Any ideas?

Only the single wire to the sender on the back of the engine feeds the gauge. The oil pressure SWITCH provides power to the choke in a non-fuel injected truck. That wire provides a power feed to the sender from the gauge and the sender provides a variable resistance to ground, based on the oil pressure, to move the gauge. If you have a wildly bouncing gauge, you either have a wildly fluctuating oil pressure, loose connection that is going from a good resistance to ground to open, or a bad sender/gauge.

Since you just did a frame swap, I'd be checking all of the wire connections to make sure they are solid between the gauge and sender and then make sure the engine is grounded to the cab(back of cylinder head to firewall) and the frame(alternator bracket to frame) with good solid wires and clean contact points. There should also be a firewall to frame ground wire on the drivers side from near the wiper motor.

 

[scape]

I verified all ground straps, but don't remember there being one from firewall to frame. I have one from cab to frame but it was located toward rear of cab on right side. Thanks

 

[kkgp81]

Ground strap everything- Battery to frame, frame to motor, motor to firewall, frame to cab, frame to bed, etc. Jumping around kinda indicates a loose ground.