thegeezer

Hey All,
I've seen this topic posted quite a bit before but i'm curious to see some opinions of my situation..

My 1982 Trans Am is a Crossfire with 263k+ miles on the clock. Not sure if the block is original or not, one day I'll yank the alternator and see if I can get to the VIN stamping. I run the car with regular 10w40 oil, usually with purolator filters. Cam is stock as far as I know and naturally the tranny is a TH-200C.

When the car is fully warmed up, the oil pressure drops, as does the idle speed. I have two other V-8 firebirds and they never drop below 15psi, but this car will drop down to what I would approximate to be 5psi on the stock meter. I did replace the sender back in 2001 and that made a slight difference, but this time I grabbed an oil pressure meter to get a mechanical reading.. Unfortunately the mechanical meter is 0-300psi so the very first tick-mark is 10psi. At a very low idle in drive (around 500-600rpm) the mechanical meter reads around 10 psi (just a tad above the 0psi peg), and at 1000rpm it is over 20psi. During normal driving, it will be around 30-40psi.

Is this anything to be worried about? This seems to be beyond the 10psi per 1000rpm rule mentioned here in the archives.. Also, I am wondering, is it asking for trouble to have my idle down so low? The engine purrs like a kitten and never stalls otherwise. So what do yall think? Keep runnin it? Boost the idle up a tad? Or be nervous about it?

-Kevin

z28monster

iTrader: (1)

replace the oil pressure sending unit... they go bad often... a while back i had the same low oil pressure deal so i first replace the sender and i fou d out it was the problem...

Vader

That IS strange. Generally, Chevy V-8s with such low mileage don't have oil pressure problems unless they've been neglected or abused. I'd suspect the pressure sending unit as well, but you can verify the dash gauge reading by installing a mechanical pressure gauge at the sensor location or at the port on the front of the block above the camshaft oil gallery.

F-BIRD'88

Turn the idle speed up. 500rpm is too low.
It may idle smooth as silk at 500rpm but the oil pump is not turning fast enough. Set the idle speed to 700-750 in gear when fully warmed up.
As long as it gets to full oil pressure (40PSI+/-) at 2000rpm when warmed up, its ok.

Vader

Idle is ECM/IAC controlled on a CFI. Target for a warm engine is in the range of 550-600 RPM in DRIVE. Not much to be done about that short of reprogramming or "cheating" the TPS.

You should be able to fit a 0-60 or 0-100 gauge to get a better look at pressure. Since you are making adequate pressure at RPM, I would not suspect any serious damage. 1 PSIG per 100 engine RPM is generally sufficient on an SBC, but we all like to see a bit more.

thegeezer

Yep Vader, the computer pretty much controls the idle. I did run thru the tbi rebalance again using my digital manometer, and the idle didn't change much. Making those adjustments is quite amusing. I had a laptop hooked up and the engine was running at 300-350rpm, I don't think I ever saw a v-8 running that slow under normal conditions.

I did replace the sender and still get the same readings.. I've run the car quite a bit since I started the post and everything seems to be fine..

Is there any way I could try and run an additive in the oil to help take out sludge, if perhaps some sludge on the pickup screen is hurting things a bit? I'd be willing to give that a whirl since I probably won't have the oil pan off anytime soon..


Kevin

RB83L69

Your oil pressure readings at normal RPMs are reasonable.

I think if you got it to idle at the right speed, your oil pressure reading would take care of itself.

thegeezer

Yep, an extra hundred rpm or two would make it look nicer.. But would the crossfire be happy like that? With a/c on, or sitting in neutral, the extra rpm's make things look better.. It's only when stopped in drive that it gets down to its lowest.

RB83L69

It should idle higher than that, like 600 or so in drive. 300 is way low.

thegeezer

no

That insanely low rpm was a reading during the tbi rebalancing.. That is done under different conditions - the idle air passages are plugged, the 2 iac motors are disconnected, and the car is in drive. At the very end of that procedure, they tell you to adjust it to be 475rpm. Running thru that procedure did boost my idle slightly. Under normal driving, the engine may get to as low as 500 in drive while stopped, but is usually a bit more (600-700).