Hey all,

I checked the search and read lots of threads regarding the questionable oil pressure sensors. But it seems most fail differently from what I'm seeing...

I have an 88 2.5 Liter with an unknown history. From what I've seen, the car has been loved and shows signs of regular maintenance.

I just got the car on the road for the first time yesterday. After a lot of work, the car is running smooth, and I really like driving it a lot. I've put about a hundred miles on it so far.

One thing I notice, that has given me some anxiety, is that once everything is up to running temperature, if I'm sitting at a light, the oil pressure gauge drops to zero. It will bounce down to zero if the idle dips (the idle is solid, but varies just a tiny bit), then as the idle recovers, the gauge does as well. There are moments, when the gauge will sit at zero for a full second or more!

Today, after a trip on the freeway, I brought the car into the garage, popped the hood, opened the oil fill cap, and watched through the window as the gauge did its thing. Though the gauge went to zero I could still see oil splash around the rockers. There is no rattling of bearings, no odor of burnt oil, nothing unusual (knock wood).

When I turn the key, the gauge does peg to the right. I've read this can be an indication of a bad sensor. So I'm thinking it's the sender and I should be ok driving the car. Right? Also, I changed the oil and filter this morning. The fresh oil had no effect on the behavior of the gauge.

Thanks in advance...

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Spent my days with a woman unkind Smoked my stuff and drank all my wine...

It could be the sending unit, but just to be sure, invest in a mechanical gauge. They're available for about $10. After bringing the engine up to operating temp, remove the electric sending unit and attach the mechanical gauge. This will give you a true reading. Then you can compare that reading to your current sending unit, or to any that you replace. It's not unusual to buy a new sending unit that is inaccurate. I have 2 new ones that show 60-80 lb at idle, when the mechanical gauge says 20 lb.

ANY car I have, I always put in a "T" with a sender for the electric gauge AND a Mechanical gauge also. very cheap & more reliable. I don't trust EITHER the factory TEMP Or OIL Gauges. your problem COULD be the sender, loose wire, Or main/rod/cam bearings. If any of them are on their way out, you will still see oil coming through the push rods.

quote Originally posted by Lou6t4gto: If any of them are on their way out, you will still see oil coming through the push rods.

If the gauge reads zero, will oil still be splashing around top? Also, if the bearings were on their way out wouldn't I be hearing a clatter (when I goose the throttle and rev it up through the range, there are no odd noises at all)? It's been doing this a lot now. My thought, is that by now, the damage would be done and there would be evidence. How long can an engine run without oil pressure, before it's obvious?

Just playing devil's advocate. I really appreciate the feedback. One verdict is great, the other one is awful.

On a similar topic, I just got my 2.8L running and it shows the pressure right above the red line at idle with a warm engine. Is that ok?

What does your oil pressure read when it's not zero? (Engine hot, idling). My 88 duke with 185,000+ miles reads just below 30 under these conditions. I use 5-30 synthetic oil.

You haven't yet mentioned what your oil pressure is doing at RPMs above idle. If it's higher than 20 to 30 psi at 2000 RPM (warm), then your engine is probably safe for now.

Several suggestions:

1) If you haven't already, check your oil level to be sure it's within normal limits. (I do not mean to be insulting here. It's sometimes the small things that get you.)

2) If in doubt, just replace the oil pressure sender. It's $20 well spent, and it will probably restore more normal gauge indications if everything else is OK.

3) If a new sender doesn't fix the problem, you may want to connect a mechanical gauge to verify what the Fiero gauge is telling you.

4) If you're still seeing low oil pressure after doing all of the above, then you need to investigate further.

5) You do not want to try to fix the problem by using heavier weight oil or miracle-in-a-can additives.

quote Originally posted by pswayne: What does your oil pressure read when it's not zero? (Engine hot, idling). My 88 duke with 185,000+ miles reads just below 30 under these conditions. I use 5-30 synthetic oil.

My oil pressure runs the same as yours. I just changed the oil to 10W40 Pennzoil for high mileage engines. The oil change didn't make a difference.

As an aside, I took the car out last night and drove it through a similar route that, in the past, has resulted in the symptoms I've seen. But this time, the oil pressure stayed higher across the board and even when the idle dipped, the oil pressure dipped as well, but not into the red as it did previously.

Cam bearings.

The rods and mains get oil before the cam bearings. Pressure is read after the cam bearings, which is why you do not hear any bottom end noises.
The gauge/sender would not read a pressure at higher rpms, if it were the problem.
If the guage is reading different pressures at different rpms, with the idle being lowest, I'm still going to say, 99 percent chance, it is your cam bearings.
New oil is thicker oil, thus the reason for the slight increase. Won't last long though. I now this is not what you want to hear, sorry, but I've been there, done that. High volume oil pump is also only a temp fix. Found that out myself, also.

Kevin

It's in the garage, right now, with "zero" oil pressure, idling like a champ. This was after a 50 mile drive. Right when I got close to home, I ran it through the gears, above 4 grand. My attitude was "why prolong the inevitable?"

Then I got home, opened the hood, pulled the oil filler cap, and watched as the oil was dancing around the rockers, even with "zero" oil pressure. At times, especially after I "goose" it, the gauge pegs itself, then settles back to zero or just above.

Does this change anything? Or am I still budgeting for a new engine?

Thanks again for all the help. I really do appreciate it.

I'm headed back down to the garage to wait for the engine to grenade.

I honestly just believe you have a gauge issue. After all this driving and trying to figure out what its doing, if you had no oil pressure, youd be hearing the lifters rattle, or a rod begin talkin to ya a little bit. One thing I feel you should do, just to prolong engine life all together, is switch to a FULL synthetic. You will be happy with the increased fuel mileage and the ability to go twice as long on a typical oil change. Synthetic will free up your engine more and perform better all around. Ive never been a fan of Penzoil but its totally your own prefference as to what you want to use. Castrol Syntec 10W30 is my oil, 365,000 miles with NO internal engine work on a 90 Grand Prix 3.1. All my fieros have shown good improvement and I run it in my 2002 WS6 LS1 at the track. 100k on the bottom end.

The one thing that bothers me is where you said:

quote When I turn the key, the gauge does peg to the right.

I am assuming the engine is off? If so, something is wrong there, it shouldn't peg with only the key on. Like fierofool & Lou6t4gto said, it's best to put a real mechanical gauge on it. Find out what the actual oil pressure is and go from there. With luck, it might only be a bad sending unit.

Mike

So I was able to connect a mechanical gauge, and it turns out it IS the sensor.

Phew!

The mechanical gauge reads over 10 psi higher. So I'm going to order a new one.

Thanks a ton for all the assistance.

Cheers!

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Spent my days with a woman unkind Smoked my stuff and drank all my wine...

Hey that's great. Your engine is ok and it's a cheap, simple fix for you..... can't beat that.

Mike

I bought an autozone sender and it showed good oil pressure as the car was warming up but after the car was at operating temperatures the oil pressure would be just above the red at around 40mph and zero at idle. I bought a GM brand oil pressure sender and it works normally now. I did listen for lifter noise when the gauge was reading zero at idle and there was no unusual noises. Because of this I will suggest you try to find a GM (AC/Delco) brand sensor.

Charlie

Thanks. I'm going to do that. I hope they aren't too difficult to find.

Do you get these mechanical gauges at Checker - Autozone etc?
sparx22

I bought mine at AutoZone. It was about $10. It's just a small round gauge with a chrome mounting bracket, designed to mount underneath the dash. Comes with a coiled nylon line and connector that screws right into the top where the sending unit goes.

Edit: The gauge isn't mounted permanently in the car. lI just use it to test oil pressure readings against what the sending unit is registering, then I replace the sending unit.

[This message has been edited by fierofool (edited 12-09-2008).]