RELLIK

I was going down the highway running around 75 MPH and my friend was in his car beside me we decided to race, I have a 1991 Z28 305 and i lost power and oil pressure but i am not leaking oil and not burning any that we can tell.,...does anyone have any idseas on what i should replace? I usually run about 32 - 35 lbs oil pressure normally now its down to 18 when idling...will it be ok for me to go ahead and drive as well?

PyRo9862

Don't drive it untill you know whats wrong. How far did you drive with no pressure?
Its one of two things, you actually lost oil pressure, or your sending unit (or a connection) is bad.
I'm not sure how to determine which, I will leave that to someone else. If you drive with no oil pressure, its almost the same as driving with no oil in the car, its very very bad (unless you want your motor to seize for some reason).

trackbird

You could have lost the oil pickup off of the oil pump. I had an 89 Formula that had the pickup fall off of it (I had good oil pressure except when on the brakes, it went to 0), but if you lost the oil pickup and are slightly low on oil, it may explain it (vibration can knock them off).

How is the oil pressure when cold? If it is fine cold but drops when the oil warms up, the pickup may have shifted towards the bottom of the pan and the suction, when applied to warm oil can pull it into vapor (it "boils" under the heat and vacuum) and that would be another possiblity.

However, I am guessing that it is more likley that the pickup fell off than the chance that it simply fell down. They are in there pretty tight.

Or, dirt stuck the bypass valve in the oil pump in a slightly released position.

There are many reasons, those are a few of them. I'm sure there will be others.

I'd make sure it is full of oil and that there is no oil in the coolant and no coolant in the oil and go from there.

Good luck!

trackbird

18 when idling, does it come up with a few revs?

PyRo9862

I got the impression that its constatnly reading 0 pressure, that couldn't be the sending unit?

trackbird

PyRo9862

Its official, i'm an idiot

RELLIK

when its cold i hold normal pressure when it warms up now im losing pressure....it is full on oil and when it warms up the pressure will raise with a few revs to about 20 - 25 tops driving at 40 MPH it stays at about 20 PSI unitl i stop then it drops back to around 18 or a little lower ... it is a tuned port injected 305

lordmetalz28

oh great i did my oil pump last year, i had to hammer the pickup in the pump, i cant wait till it falls out, is that a big problem when they fall out.

aklim

Lets stop this crap and attach a mechanical oil pressure gauge to the sender. BTW, if you really had 0 psi of oil your engine would be rattling around in a short while.

trackbird

I agree that a mechanical gauge will verify the actual oil pressure and eliminate a bad sending unit or faulty gauge. However, he didn't say 0 oil pressure, he said it is lower than it used to be.

Stick a mechanical gauge on it and see what it reads and we'll go from there.

aklim

My bad. Get a gauge on it anyways. That way you know for certain if it is low or not. If your pump has to be removed, tack weld the pickup tube onto it so you know it will not fall of again.

18 psi is really low. Mine idles at 30 psi. If it was truely that low, either the pump is faulty or the bearings might be shot.

90rocz

The 1991 and 1992 models ran a standard pressure/standard volume pump, normal is only 32@2000+, while earlier models like mine ran 55psi@2000+, if you end up replacing the pump get one for a pre-'91 "Z28"...
Things that can lower oil pressure:
1)high volume filter..like Duetch(sp?)
2)engine wear...if with new oil it drops off badly after warm up.
3)cheap oil or dirty worn out oil.
4)worn oil pump, large clearances..
*Remember tho, it only requires 10psi/ 1,000 rpm to survive..and some say only 30psi max is enough for a daily, but for abusive driving I prefer a "pre-1991 Z28 oil pump"...

aklim

Not sure about the pre or post 90 pump but I got a Melling Standard pressure High Volume pump and get about 30 psi on warm idle.

RELLIK

i have aftermarket mechanical guages mountes to my dash, I did however replace my oil with cheaper oil this last oil change but I will be sure to check my pick up tube and replace the oil with some that is better can anyone suggest a better oil then Penzoil 10 W30?