Hey guys,

Been awhile since I've posted. I picked up an '84 trans am with a 350 tpi out of an '88 Trans Am. I've already concluded that the fuel pump relay is bad, as the pump does not energize when you turn the key on. But it does start after a bit of cranking. The current problem I'm having is the oil pressure. Key on engine not running the guage zeros. Engine running cold, 80 psi plus. Engine running at operating temp, 70 psi low rpm, 80 psi plus high rpm. There are no oil leaks, there are no god awful noises coming from the engine. Everything seems fine except the guage reading high. My first thought is the oil pressure sending unit. Would I be better off checking something else first? Thank you for your help.

 

I'd remove the sending unit and try hooking up a mechanical gauge. If it reads the same then it's obviously not your gauge or sender.

 

I don't have a mechanical guage...yet. Would it work to swap the sender with the one out of my '85 T/A 305 4BBL? I know that one works.

 

Do the senders look the same?
If it really bothers you a mechanical gauge will put your mind at ease.
Mine's pegged the whole time I drive my car unless the drive lasts longer than 45 mins. I'd only be worried if it was reading low.

 

the down fall to most motors is that they run out of oil (low press) sounds like a high pres. oil pump to me.

 

Check this out. My car was originally an '84 H.O. 305. I read somewhere that this was the only third gen firebird that came with an 80 psi oil pressure guage. If this is correct (is it?). Then the pressure sender in the transplanted 350 tpi would be for a 60 psi guage. This would cause the wrong voltage to be sent to the 80 psi guage, resulting in an inaccurate reading. Can anyone back me up on this?

 

The 84 HO cars had a 60 psi gauge, same as all the other V8 cars. I don't know where you read that but it's wrong.

The 80 psi gauge was in 6-cyl cars.

The gauge itself is the exactly same, electrically; just has different numbers painted on its scale. The sending units are different, to make up for the difference, such that they reach the same electrical resistance at the 2 different specs of applied psi. So for example if you put a 80 psi sender into a car with a 60 psi gauge and the system has 40 psi, the gauge will go to half scale which corresponds to a reading of 30 psi.

All that aside, it sounds like you have a defective oil sending unit. I wouldn't bother with a mech gauge. You gotta go buy the gauge, then install it which is a hassle, then it'll tell you that the oil pressure is fine so your stock system must be AFU which of course will be the sending unit, so then you'll have to go buy the sending unit and uninstall the gauge and install the sending unit. About 3 or 4 times as much money and at least twice the work, compared to just changing out the SU in the first place... which is the problem with these gauges about 95% or more of the time anyway.

Kind of reminds me of some eqpt I had to work on some years ago. I had probably 30 of them in my area. It had an audio amp with about 20 electrolytic caps in it. I had got it down to a science of taking it apart and finding THE bad one and changing it out. After about the 3rd time of taking the same one apart twice in less than a week for successive failed caps, I learned my lesson, and every time I tore one down, I shotgunned them ALL. The lesson being, sometimes the easiest, quickest, and cheapest method of troubleshooting, is to just REPLACE IT. Not always, but SOMETIMES. This is one of those times, where troubleshooting doesn't save you anything because it's more work and money than swapping it out.

 

Man, I wish I would have read that before I went and put in a mechanical guage. Cost me 16.99 plus about an hours work. But everything is fine. I think I'll just leave the mech guage installed for now. Like you said, now that I did it, I would have to undo it As for why someone would have put a V6 guage cluster in a Trans Am All of you guys are great! Thanks a whole bunch.