Hello,

My fiero, 1987 GT Auto, had low pressure at idel once the engine warms up. I tried to fix this by doing the following:
-pulled the pan and replace the oil pump, screen.
-changed the oil pressure sensor (sending unit)

Now I find that my oil pressure drops even faster.

By the way, when I say it drops, I mean like in the RED!!!

Could this just be the gauge? If so how would I check this?

The engine was supposed to have been rebuilt the year before I bought it, which would be about 5-6years ago.

I have no oil leaks or consumption.

Any help would be great.

Until this is fixed, I guess she will just sit in the garage.

Thanks,
Ken

sounds like your bearings are shot, but you say it was rebuilt... curious. i would suggest that you try running a heavier weight oil like 20-w30, and see if that helps, if it does, bad bearings, if not, let us know.

------------------

Currently a student at Wyotech in Sacramento.
1987 Pontiac Fiero GT, 151,000 miles! decklid window, silver guages. rear ended someone, and now the rebuilding starts! More pics of my 87 GT can be found here
1985 Pontiac Fiero 2m4 auto, 222K miles and counting <-my first car, and i still cant get rid of her!
2005 Jeep Grand Cherokee 3.7L 4x4, 62K <-Daily driver
A 4 year olds knowledge of science: No matter how much jello you put into a swimming pool you still can't walk on water.

Thanks for the looks and the info.

I was hoping not to hear the answer you gave me! Removing the cam and replacing the bearings sound like alot of work.

I guess I will try to check the gauge this weekend but I have a feeling it is the bearings too.

Is it possible that the new oil pump is crap? I bought it at Autozone, it's a Duralast. But the pressure sending unit is from fierostore.

How do I convert the voltage going to the pressure gauge to actual pressure?

Thanks again,
Ken

Get you a cheepo manuel guage with the plastic hose to hook up to see if the drop is real, or the electronic guage acting up. You can get one at the parts houses for around 12-15 bucks. You will know for sure in about 5- 6 min's time

I would suggest you verify the pressure with a mechanical guage.
stock automotive guages are not the most accurate.
next, rod bearing & main bearings can be replaced by dropping the oil pan - not so bad a job
yes - cam bearings is no fun. I am about to do that job

quote Originally posted by Baby_Blue: I was hoping not to hear the answer you gave me! Removing the cam and replacing the bearings sound like alot of work. I guess I will try to check the gauge this weekend but I have a feeling it is the bearings too..................................

Not the Cam bearings but the Main Bearings.

Main bearings is the oil pressure factor.

quote Originally posted by Pyrthian: next, rod bearing & main bearings can be replaced by dropping the oil pan - not so bad a job

While this is true...................the odds are against you of regaining oil pressure ( already tried it ) putting bearings in without machining completly gone through & checked or match maching performed, it winds up being a waste of bearings.

quote Originally posted by PURPLE REIGN: While this is true...................the odds are against you of regaining oil pressure ( already tried it ) putting bearings in without machining completly gone through & checked or match maching performed, it winds up being a waste of bearings.

depends on the if the bearings are bad or just worn. I had to do this also, and was lucky. was just worn bearings - didnt need to remove crank & get it machined. yes, I know odds are - the crank is wrecked.

quote Originally posted by PURPLE REIGN: Not the Cam bearings but the Main Bearings. Main bearings is the oil pressure factor.

Not necessarily correct. In the 2.8 installed in Fieros, the oil goes up to the cam bearings before it goes back down to the crankshaft. High clearance around the cam bearings can result in loss of oil pressure at the main and rod bearings.

Thanks again for the advice.

I guess if it comes down to opening the engine up, then I will change both the main bearings and the Cam bearings.

I wonder if these were changed in the rebuild, or if they just put in some shitty ass bearings.

I will check the pressure this weekend...then if needed try putting in some thicker oil, so as to last until the end of the season.

It was mentioned to use 20W30...any other suggestions.

I beleive that I have in 10W30 right now.

Thanks,
Ken

The crackshaft main bearings, are they Journal bearings? If so there has to be a very good surface finish on the crackshaft right?

quote Originally posted by josef644: Get you a cheepo manuel guage with the plastic hose to hook up to see if the drop is real, or the electronic guage acting up. You can get one at the parts houses for around 12-15 bucks. You will know for sure in about 5- 6 min's time

I did exactly this same thing. I found gauge test procedures on PFF and the circuit checked out ok. After I warmed the engine to operating temp, I removed the electronic sending unit and installed the mechanical. Found that the brand new one was way way high. Probably of the same bad batch that The Fiero Factory received. Anyway, after getting a reading at hot idle, I swapped around the 4 electronic sending units I have on hand, until I found one that agreed with the idle pressure shown on the mechanical gauge.

I don't really care what it shows at road speed, just as long as when I stop at a light or stop sign, it shows that my idle oil pressure is above 20 lb. I figure that if my idle pressure is sufficient, then it can only go up at road speed.

Oil change with Lucas oil treatment might help.

quote Originally posted by Marvin McInnis: Not necessarily correct. In the 2.8 installed in Fieros, the oil goes up to the cam bearings before it goes back down to the crankshaft. High clearance around the cam bearings can result in loss of oil pressure at the main and rod bearings.

Yep, and of the several engines I've dismantled I've found that it's the cam and rod bearings that were worn/failed, the main bearings were always in good shape. The only exception was a motor that came out of a Fiero that died by being chased by cops until the cooling system got ripped out by running over something and the engine was run at full throttle until it just wouldn't move the car one more inch. That one had all the bearings scored and damaged, and the oil was burned into charcoal in the lifter valley and oil passages in the block.

JazzMan

Man.... Jazzman, you are hard on an engine

J.

I swapped my gauge with another out of my other fireo and the reading was the same, so it isn't the gauge. Then I swapped out my new pressure sending unit with one off of my spare engine and it no longer is dropping in the red. I also inspected my old sending unit and it seemed to been damaged due to rust, so I guess it was due to be changed. As of now it looks good, but I guess I'll take it out for a good drive tomorrow and see what happens.

Thanks guys, I'll let you all know what gives tomorrow.

Glad to hear you got it figured out. But before going out and buying new main or rod bearings, make sure that you plastiguage them first to make sure that is even the problem.

I have found most oil pressure problems turned out to be worn cam bearings and not the mains as a lot of people think.

As others have said, get you a cheap mechanical gauge and verifty, so you can sleep at night.

John Stricker

quote Originally posted by Baby_Blue: I swapped my gauge with another out of my other fireo and the reading was the same, so it isn't the gauge. Then I swapped out my new pressure sending unit with one off of my spare engine and it no longer is dropping in the red. I also inspected my old sending unit and it seemed to been damaged due to rust, so I guess it was due to be changed. As of now it looks good, but I guess I'll take it out for a good drive tomorrow and see what happens. Thanks guys, I'll let you all know what gives tomorrow.

ok so i just put this new 3.1 bored .30 over in my car last week and i am having the same issue... everything in this motor its bran new only after it get really warm like when i get home from work or just driving it and my idle drops below 900. I have some idle issue that is bugging me too... it will idle but its jumpy between 1300 and 800 back and forth all the time. i think it might be the cam that i have in it but i dont know. The cam does have a slight lope at idle and i think this might be the issue... i have replaces the iac and tps i dont have an egr system so i know that thers no vacuum leak... other than that i have no clue where to look. i think i have about 800 miles on this motor.

So I took out my car for a nice drive today, the pressure is now staying out of the red, even once the engine hits its max temp. Thus I conclude that the faulty new pressure sending unit was the culprit. Thanks for everyone who helped me through this one.

Another issue I ran into is a problem with "hot start". I just wrapped up the starter with insulation wrap, and hopefully this will solve that proble.

Thanks again,
Ken