I have a 79 F250 with a 460. Approx 74,000 miles. Engine is original. I'm the third owner and knew the previous two so I know the mileage is correct. The only work performed on it was a water pump replacement, P/S pump replaced, and the smog pump was replaced with and Edelbrock carb installed. All of the other gauges work properly. The oil guage shows no pressure. I've replaced the gauge with a new with no changes. Bypassing the sending unit will jump the needle to high. The IVR has been replaced. I have installed an A/M gauge and it shows 70 at start and 25-30 at operating temperature. Temp and fuel gauges work fine. I have changed the sending unit (numerous times) and it works briefly and then back to the same. If I was dealing with a grounding issue then I would suspect that the temp gauge would be giving me problems also. If it was a problem with the printed circuit board then I would suspect the gauge would be dead when I jump the sending unit. I did have the both the factory and A/M gauge plumbed in together via a tee at the block with the factory gauge showing no pressure while the A/M showed it as good. Am I simply getting bad sending units? It used to show high pressure at highway speeds. I know it would be simple to just use the A/M gauge but the truck is all original and too nice.

 

check the resistance from the pressure sender connection to ground with the engine off and compare to the resistance with engine running. If the sender appears to be ok, then start chasing the wire back to the cluster (including the cluster connector and copper traces on the cluster backing)...

 

Reads like a bad sender. Go easy on the seal tape too, it needs a ground through the threads.

 

Try to find OEM on the bay. They come with a sealant already on sending unit. If other gauges work IVR was ok.

 

Are you getting a warning light sending unit from the parts store, or are they giving you a pressure gauge sender? Many parts store employees don't know the difference.

 

I've seen coworkers do that very thing when I was part timer at our AAP.


Not sure of your's location, but this on a 351M, the sender should look like it except for the pine needles.