Here goes- I have a 95 Z28 auto. 118k miles, but runs very well. I have kept up with all the maintenance, the car isn't hard to start, doesn't knock, use oil or anything. Basically, from what I can tell the motor is in great shape. Anyhoo, doing some second gear pulls I realized something very strange is happening to my oil pressure.

If I start a pull in second at about 3500 rpm, the oil pressure is at about 40 psi. When I hit the gas, at about 4000 rpm the oil pressure drops all of a sudden to 25 psi At first I would let off, scared that the motor would spin a bearing because of maybe some oil starvation somewhere. I changed the oil last night, and even put in just a little extra, and tried a second gear pull. This time I stayed in it. The oil pressure did the same thing as before, but when I stayed on the gas, the pressure came back up again after it dropped off It came up to about 50 psi at redline.

So I ruled out not having enough oil, I thought maybe the problem could be caused by the bypass valve opening, but I really don't think that would cause the oil pressure to drop 15 psi

Has anyone had this happen before or have any thoughts????

John

 

I have sen this discussed here before,maybe in advanced tech.Sound like bearing problems,when under load it allows the oil to flow out instead of where it should.Thats about my best description,sorry.You might want to search in that forum.Hope it isnt too bad.

 

I have this same problem, and ive had for 2 years, since ive had my car. Ive posted on here as well as many other message boards and ive never found anyone who had something to specifically fix it, or even diagnose it for that matter. Ive been goin to the track and racing once a month the whole time and i dont have any problems, and it still runs like a raped-ape! I was cautious at first but ive just kinda put it in the back of my head. That may be a bad idea, but in my opinion, if there was something really bad, then I would definitely know about it by now.

Good luck and let me know if you find anything out.

-Ryan

 

I believe this is just a strange cavitation problem that many people have had with the stock pump. If that's your problem the only real fix is to install a rebuilt one with the "slit" across the pump face to help equalize pressure across the pump gears. You should be able to dig up some info as it's been discussed many times on here and the email lists.

 

Does anyone have some more info on what I can do?? If it's a bearing problem I need to fix it, if it's a pump problem I need to get it solved before the heads and cam go on. I'm gonna try and dig up as much info as possible, but I have to go to work now, and any help or info would be greatly appreciated.

John

 

I would try a Melling High Volume pump.

 

You guys who have this symptom are describing 100% the symptom you get if you lose the pickup off of the oil pump. Once you pump a quart or so out of the pan (getting up around 4000 RPM) the pump starts to pull air and the pressure falls off. There are a couple of way to find out if the pickup is on there...

Try to locate a "borescope" and go through the drain plug hole and see if the pump still has the pickup attached firmly. Sometimes you can tap on the bottom of the pan with a rubber mallet and the bottom of the pan will flex enough so that the pickup will bounce around and you will be able to hear it clunking in there.

Good luck...

 

Never thought of that!!! It's worth a shot, I'll see what I can find.

John