Two bad new oil pressure sensors? Tell me I am wrong.

I noticed my oil pressure gauge reading low last week. At cold start up it was just over 15psi and dropped to maybe 5 psi when hot. This had me concerned so I took out the sensor and hooked up a good quality pressure gauge.
Gauge shows 38psi at cold startup which made me feel better, so I assume the sender is going bad and ordered a new sender.
New sender shows the gauge pegged high when I turn the key on and stays there when the engine started. I assume I just got a bad sensor so I returned it and exchanged for another.
2nd sensor does the same thing?? I ran a extra ground from the sensor case to a frame ground to ensure a bad ground was not the issue. No difference.

Measured the resistance on my original sender and it was around 28ohms on the bench. Measured the 2nd sensor that failed and it shows open.
The truck pressure gauge shows pegged high with no sensor connected and exactly the same when the new sensor is installed.
Am I missing something? I can only assume I got 2 bad sensors, however unlikely.
I purchased them from Napa. OP6640SB was the part number. The sensors are stamped 60 on the housing which is the same as the original I removed and corresponds with the trucks pressure gauge, and all the online charts show this to be the correct sensor.
I guess the next one will need to be from somewhere else.

Never mind reread your post yoi already answered what I was asking. Sorry.

You're wrong. Glad I could help.

In my experience, shorting the sensor wire to ground will peg the gauge. If it's showing full high even when not connected, something in the circuit is grounded.

Although, Roger's diagram shows an open circuit doing that, so maybe an '80 is different. Either way, if it's pegging without a sensor connected something probably happened to the wiring when you chaged the sender.

Blue Ox said:

In my experience, shorting the sensor wire to ground will peg the gauge. If it's showing full high even when not connected, something in the circuit is grounded.

Although, Roger's diagram shows an open circuit doing that, so maybe an '80 is different. Either way, if it's pegging without a sensor connected something probably happened to the wiring when you chaged the sender.

Click to expand...

The original sender is back in place until another arrives and it works as before. 0 psi when the truck is off, truck running =15psi. I don't think I caused an issue with any wiring, but I appreciate the suggestion.

Are you ordering senders that match the year of your gauge. It's not uncommon for people to order the sender based on engine year. That is incorrect. Year of gauge and year of sender need to match. If they do sounds like your problem is at the instrument cluster it's self.My next step would be pull a wiring schematic,verify if there are voltage stabilizers ,or resister in the circuit,test those and the gauge itself. If those are good it has to be an issue with the printed circuit.

I put a standard motor products oil.pressure sender on my 79k10 350 and was reading like your stating. 15psi going down road and almost 0 at idle. Found a ac.delco oil pressure sender and now 45-50 going down road and 30 at idle. Also hooked up mechanical guage to confirm before installing ac...same reading. May want to search for ac delco sender.

Why not install a mechanical gauge to validate what is really going on?

The sensor shouldn't need a separate ground. They didn't come from the factory that way, why change it now?

I personally had two oil pressure sensors go bad on my truck with very little run time on either.

You can see how new this one looks and it was already bad.

There is a sender for "idiot lights" and a different sender for an actual OEM PSI reading gauge too.

3rd sensor received. 19 ohms resistance out of the box.
Gauge now shows 0psi with the key on, 38psi at cold startup exactly like the mechanical gauge I had used to check the pressure before.
After a few minutes when the idle settled back down to normal it was 32-34psi which is also the same as the mechanical gauge.
So 3rd time is a charm and every thing is back to normal.
So if anyone needs a sensor do not waste your money on the NAPA MPI OP6640SB (1 year warranty)
I ordered their other sensor MPI OP6640 (3 year warranty) Hopefully it lasts a while, but I will probably install a mechanical gauge or maybe one of those 3 gauge kits over the winter.