93 4.3L V6 low/no oil pressure. already changed pump. Help please!

[mirrox]

First off, hello!

Here's the skinny...
I've got a 93 chevy cheyenne 1500.
4.3L V6.
Auto trans
2 wheel drive

Problem: when I start the truck the guages all zero and then go up to what they're reading. The oil pressure hits about 30psi (mid guage) then as the truck idles, the pressure drops. If i accelerate the engine or drive the guage changes and reads higher pressure. Then when the engine idles, the pressure falls. Seems like each time it falls, it falls lower. About the time the truck his 210F degrees the oil pressure is almost 0 at redline. This scares me.

Now, the weird part:
The engine runs totally smooth. No lifters knocking. no screaming of dry metal on metal. No unordinary oil leaks (as in no HUGE leaks). It runs strong and and quiet with no loss of power or any lag.

Attempted Remedies:
I've already changed the oil pump. (primed pump, installed with new intake screen, new rubber pan gasket, new filter and added 4qts quaker state with 1qt Lucas).

I'm getting ready to throw in a new oil pressure sending sensor.
Could it be anything else?

Any suggestions are most appreciated. Sorry for the long read, just trying to be detailed.

Thanks,
Christopher

[broughy84]

if it isn't the sensor, which is most likely is, then you could have some very worn bearings on the crank.

[wrparks]

Yea, I would bet the oil pressure sending unit is bad. I had one replaced once and the symptoms were very similar.

[mikejohnson]

91-94 are notorious for their crappy guage dashes. the sending units are almost always fine, its just the dash, at which point you have to buy a seperately mounted guage, or replace the entire dash. to make sure your sending unit is good, when you crank the truck, the guage should go all the way full, and then return to its nonworking state

[sub006]

Sounds like it's an instrumentation problem, all right.

By the way, all you guys, the word is spelled G-A-U-G-E. Honest!

[BleedDodge]

Originally Posted by sub006

By the way, all you guys, the word is spelled G-A-U-G-E. Honest!

Did anyone spell it any other way in this topic?

[jcdubbu]

i had the same problem in my 3/4 ton 350 motor. i replaced the oil pump, then converted the gauge to a manual one still read low to zero oil pressure after engine was warm. then a buddy told me to rebuild the lower end of the motor because i had worn bearings. he was right....now running strong at 50 psi

[echo's dad]

Hopefully you've figured it out by now...if not:

take out the sender and get/borrow a mechanical guage...
to test your dashboard gauge, unplug the sender...the needle will go to zero or all full...then ground the sender wire and it should go full stop the other way.

It does sound like you've got a worn motor though...

[glenncof]

I like to nail down the problem before throwing parts at it.

Check sender with ohm meter after determining what it should be from a repair manual or do web search. Usually there is a table showing resistance vs. pressure. Tolerance is usually very wide, +/- 10-20%