[moonrider1]

OK guys I was driving my 79 one day an noticed that the oil pressure guage dropped to zero. I pulled over immediately to try to determine if my oil pump died on me. It appears to be working fine and I am having no engine noises, smoke or over heating problems so I assumed the sending unit was bad. I replaced it and the guage still reads zero. What is the best way to trouble shoot this problem and determine if the guage is bad or if there is a wiring short? I looked at the wiring in the engine compartment and it does not appear to be shorted anywhere. Any ideas?

[firebird_racer_78]

That's sounds interesting, I'm not sure what causes it, but I know that the oil pressure guages on the late 70's Trans Am's are notorious for being faulty. At least that's what I can gather, or it's just a strange coincidence, because I have a 78 TA my brother's gots a 79 TA and my friend has a 79 10th Anniversary TA and an 81, and with all of them either they don't work or bounce around alot. If you do figure out what happened please post.

[Razorhorn]

Originally Posted by moonrider1

OK guys I was driving my 79 one day an noticed that the oil pressure guage dropped to zero. I pulled over immediately to try to determine if my oil pump died on me. It appears to be working fine and I am having no engine noises, smoke or over heating problems so I assumed the sending unit was bad. I replaced it and the guage still reads zero. What is the best way to trouble shoot this problem and determine if the guage is bad or if there is a wiring short? I looked at the wiring in the engine compartment and it does not appear to be shorted anywhere. Any ideas?

Betcha a donut you got a faulty sending unit.

Here's how to test the wiring to the gauge and the gauge itself. With the ignition key turned on (motor not running!), short the sending unit wire to the engine block (effectively grounding it). Have your wife read the gauge. If it goes to maximum pressure, your wiring and gauge are good and it's the sending unit. If it doesn't budge, let us know and we'll take it from there.

[moonrider1]

Thanks Razorhorn. I did try the ground the wiring harness and guage test and the guage did not move with the key on and the wire grounded. I'm assuming now that I have a short in the harness or the guage itself is bad. I guess I need to know where to go from here to isolate the problem.
Thanks again for the help

[Razorhorn]

Hmmm. I aint giving up on winning a donut yet. Let me check out my kids car tonight and I'll get back to you. I might have it backwards...might be on the oil sending unit disconnecting the circuit pegs the gauge with the ign on (engine off) and then shorting it to ground zeros the gauge. Sorry - I can't remember off the top of my head. I just troubleshot the temp sender on my Vette and I may have them backwards...

[kevin.1]

I test gauges/wiring in same fashion as Razorhorn's initial post. However, I short the sending wire to ground and check gauge, then short to battery(+) and check gauge. In one case, the gauge moves to max and in other case it moves to min.

[P@blo]

Originally Posted by kevin.1

I test gauges/wiring in same fashion as Razorhorn's initial post. However, I short the sending wire to ground and check gauge, then short to battery(+) and check gauge. In one case, the gauge moves to max and in other case it moves to min.

I wanted to provide my update. Oil pressure gauge would not move from 20psi. Remove plug at sender and ground it again with no results.

Jumped from the positive on the battery ton the sending unit plug and the gauge pegged. Removed the battery jumper and the gauge returned to zero. Then I plugged the sending unit back in and the gauge started working. Looks like the gauge was stuck and works perfectly now.

Hopefully this information helps others.