Question : Loss of Oil pressure during acceleration

[Cidacious]

!!Newb alert!! Sorry folks getting my feet wet here...
I just bought this 91 GTP 3.4l 5 speed w/ 96k. At idle hot it is at 40psi. At cruise it is at 70 - 75psi. at WOT it goes to 79psi. Valvoline 5W-30 Full synthetic 5 quarts. If I go near WOT especially in 2nd through 4th gears (not first and Fifth for some reason) the guage will either fluctuate like mad from 20psi to 40psi and sometimes dropping to 0psi and setting off the light. This is especially bad in 4th at WOT it will stay at 0psi and the check guages light will come on until I let off a bit. I replaced the sending unit with a new one, and replaced the Fram filter with an AC delco one. (thanks to a suggestion thread I read by Pocket-Rocket I went from 20psi at idle to 40psi!! I need to buy one for my other GTP because it has one in it too) There is no associated valve train noise with it either. It just purrs right along like there is no problem. It just started doing it last week, and I have only driven it lightly since it started. It is still doing it even after the two changes. I know the next step is buying a mecha one, and probably tape it to the outside of the windshield while I drive it, but wanted to know if anyone has had this problem, or where I should start looking.

[Ghettoracer]

Im guessing the senders in our cars are electronic so the first thing I would do is trace the oil press sender wire and see if its not touching any bare metal cause it could be jumping from the wire to another metal surface and causing a false signal to your gauge. If not the wire, I would put a fingernail worth of oil past the top of the fill line on the dipstick and see if it does it again. Could be that when you are going to WOT, the oil pump may be sucking up more oil causing your sensor to think its getting low making the gauge to fluctuate like that. It did it to my coolant gauge just to find out that when I filled the coolant to the very top it stopped fluctuating.

[pocket-rocket]

I personally would think that if the actual oil pressure were dropping to 0 you would have a butt load of lifter tick for one thing, and it would do it only in the lower gears, including 1st. Then again, my logic isn't the same as everyone elses logic. I agree with the thought of grabbing a mechanical gauge and hooking it up. What I think you are probably going to find is that you have a chaffed wire somewhere on your OPSU, but it's kind of odd that it doesn't do it in 1st gear. I know even with good oil pressure after a hart drive, I can get my lifters to tick bad (non updated oiling in the top end), so I know for a fact you would hear something if you really didn't have any oil pressure. BTW, welcome to the board

[RedZMonte]

was the old oil in the car pretty sludgy? ive seen penzoil and others sludge up and under acceloration it sucks up the sludge and oil pressure drops like a rock.

wonder if its the guage/cluster that has a problem... like they said, verify it has good oil pressure from there it could be a bad wire or a fudged up cluster.



S

[pocket-rocket]

Well after reading this post:

http://60degreev6.com/forum/f105/91-gtp-3-4l-5-speed-engine-wiring-t44415

I'm pretty convinced it's a wiring issue.

[Cidacious]

Thanks guys! I'll start with wiring, then move from there!!

[Cidacious]

Fixed! Had wife watch cluster while I moved wires around. The plate on the passenger front shock tower was gone along with wire snake on the c100 bundle. The insulation rubbed through on the power steering line so it would ground there when the engine would move under acceleration. Thanks guys!

[pocket-rocket]

Aw... we don't have a w00t smiley.... Good deal man I would rather see it be an electrical issue than a mechanical. Much easier to fix, cheaper too!