Flaky oil pressure gauge in my 1986 GP 305?

[ilduce]

Supposedly the engine is rebuilt. Well, whoever did it had crappy vacuum line hygiene and I threw about 25 feet of new shiny rubber in there. Pretty bad hygiene on the sending units, too. But, I'm real bad with instrument clusters and anything electrical other than installing speakers and a radio. I need some help!

When I bought it all the gauges worked except the oil pressure. I've got that, water temp, volts, and fuel. Until today every one except the oil pressure has worked, and reliably. Today when I was warming it up I noticed the oil pressure read 40 psi. My cigarette almost fell out of my mouth and I was a happy fella. Then it went flacid! Yeah, went right back to zero. I also thought my temp wasn't working after that, but I think I did see it move, it could have been gauge paranoia.

So, since the gauge apparently has power going to it, should I assume the sending unit is shot? I don't even know where it is. I have a LG4 305 engine. Last weekend I changed out the oil. The filter was on real tight so I banged around with my filter wrench. I also just had twin pipes run from the manifolds back on my car at a muffler shop. Could any of this work have banged the unit and made the gauge work today for a minute or so?

If it's the unit, what tools do I need and how easy is it?

 

[monte olrac]

should be behind the distributor if its a chevy motor :http://www.oreillyauto.com/site/c/d...odel=Grand+Prix&vi=1255340&pt=03438&ppt=C0039

 

[AlanB]

An easy way to test the gauge and wiring is to disconnect the wire from the sending unit. With the wire disconnected the gauge should read max pressure. If you then ground the wire, the gauge should read zero. If either test does not work then you have a problem with your gauge or wiring. If both tests work then you should replace the sending unit.

As mentioned above, the sending unit on a Chevy should be mounted right next to the distributor, driver's side, at the base of the intake. You have to really lean in and move stuff out of the way to find it. Keep in mind that the sending unit for a gauge is different than the one shown in the O'Reilly photo, which is for a light. The gauge unit is larger with a metal case. I'll see if I can find a photo.

 

[monte olrac]

thats the sending unit i had on my monte, with a guage

 

[ilduce]

Well, I haven't even checked the wire going to the unit. I drove it the other day and saw my water temp gauge wasn't doing anything. At least I have fuel and battery left. Should I just go and wiggle the wires going to the sending units and see if that helps? I hope it's not the gauges. Where is the unit for the water located?