As the engine gets warmer the oil presure goes down. & when the it gets to the hotest temp, like around 200-220 the oil presure wont go above 30 (this is going 75 mph on the highway). What bothers me the most is that every time I stop, like in a light or eaven for a quick stop sign the presure will drop to "0" until I rev it up. Im woried that this is going to mess my engine up!
By the way is an 88 305 TPI Auto.

 

I had the same problem in my 88 GTA with a 305 TPI, it was the sensor for the oil presure that was bad or something, can't remember exactly.

I tought at the time, like you, that my engine was done for, but after someone replaced the part for me, everythings back to normal...

How many miles do you have on the car?

 

Replace your oil pressure sending unit. Its located on the back of the block, near the firewall. The same thing happened to my car earlier this summer. Installed the new sensor and good as new


You'd definitely know if your car had 0 oil pressure, as your rockers and lifters would be clacking away ...very loudly.

 

yea and also your pressure will be higher at cooler temps because the viscosity of the oil gets thinner as temps go up... so hotter the oil the thinner it gets witchs makes pressures go down... if your temps are that high check to see if there is any leaves or build up blocking your radiator... thats what happend to mine over the years.. i cleaned it out and bam... lower temps all the time now... my car had the same problem... but yes it is a good point that your oil pressure sending unit may be bad... never thought of that... i also heard that most of the stock gauges arent very acurate....(thats what shifty told me)

 

she just reached 107,000 miles

 

How loudly exactly? I ask because my car also has 0psi when I start it up after I installed my longtubes. There's no noticable noise from the lifter valley, but tons of smoke, which i believe (and hope) to be the paint on the headers burning off. I haven't driven it yet and it has only been idling for the time being, so how long would it take for the valve train to start screaming?

 

Loud enough where you would shut it down immediately. The smoke is from the new paint and oil on your headers (putting your hands on them also puts on oil from your skin, which smokes off too).

If an engine had literally 0 oil pressure, the valvetrain would be screaming...and would seize up pretty quickly.

 

How close are you to an oil change? Does this happen all the time only near an oil change?

If it only near an oil change, put in a quart and see what happens.

Scott

 

In my case, the oil and filter and everything have less than 100 miles on it. I think it may be a sensor problem.

TunePort, thanks for that really helpful info. I was worried about just letting it run due to the lack of oil pressure.

Alexcoqui: sorry, didn't mean to hijack your thread.

 

Dont worry about it.

Scott you are right is usually at the same time when she is due to an oil change & when I do change the oil this problem stops but not this time. I did the oil change and it kept on telling me that the oil pressure is low. So I checked the oil level & its fine. By the way my battery gauge starting acting up about the same time but Im not a 100% sure. what it does is that it jumps, specialy when I acelerate it goes crazy. I checked the battery and its fine, the alternator is charging but is not a steady flow of charge so Im guesing is starting to go bad. Im not shure if one thing has to do with the other. Im a bit confused right now.

 

By the way where is exactly the oil pressure sending unit? (does some one have a pic of it?) & how hard is it to change, I mean do I have to remove stuff that is blocking my access to it? & one more thing, do they sell them in like lets say Pep Boys or Discount Auto Parts stores?

 

Right above the oil filter I believe. No pics though and I don't know whats in the way if anything.

Just pop the hood and check. If you can see where your oil filter is, you'll see the sensor.

Scott

 

 

The sensor for the guage is at the back of the block, right beside the distributor. The one above the oil filter is "backup" power for the fuel pump. Turns it on when oil pressure reaches some predetermined level. (about 5psi I think)

 

isn't there a sensor for no oil pressure? or is that the one for the fuel turn on? i know one is behind the distributor( sensor ) whats the one above the filter? i have an 85 does it vary with year also?

alex what year your ride?

 

OK, this is what I got is suposed to be the "Oil Pressure Switch". I havnt looked on the back of my engine for it but when I do Ill take some more pictures of the location for further reference. Hope this helps someone.

 

Alex thats the one that shuts off the fuel pump on some cars when the oil pressure is really low.

What you need is called an "Oil Pressure Sending Unit" . It shoudl be gold in color and cylinder shaped.

 

So Ill have to go back tomorrow to change it. At least we now know what it doesnt look like.

thanks for the quick reply bro.

 

The pressure switch above the oil filter supplies power to the fuel pump when oil pressure reaches a pre-determined level. There never was a low pressure shut-off switch on these cars. (otherwise, your car would not start EVER until oil pressure came up. that would be most noticable after an oil change.) This switch was put in as a back-up, in case the fuel pump relay failed, the car would still (eventually) start.

Low oil pressure fuel pump shut off is a MYTH!

The oil pressure sending unit sits behind, and to the left of the distributor. There is a 90* fitting that goes into the hole immediately behind the intake, and the sensor screws into that. (careful, these guys can break pretty easy, please don't ask how I know that.....) The sensors are notorius for failure, and inaccurate readings. GM used to be able to make a pressure sensor that would outlast the motor, not sure why they decided to replace it with something that a simple oil change could possibly kill. (maybe they were taking a lesson from Microsoft?)

 

Are you sure? It looks like from the wiring diagram that the fuel pump is turned on when pressure is high, and off when pressure is low, based on the sender unit's reading. BTW, this problem is almost certainly your sender unit. I changed the oil and the oil pressure reading dropped. It turned out to be the sender after I tested the system with a mechanical guage. The senders are known to die, you could have put it over the edge by bumping it in your header install or something.

 

HE IS 100% CORRECT.
I went round and round with this issue when I built my harness.
I thought the diagrams were wrong. The distributor ref pulse makes the ECM kick the fuel pump relay for two seconds (or so) each time a pulse is detected.
The oil pressure switch will turn on the pump directly if the relay goes bad.
Niether of them can override to shut off the pump.
ie; if the oil psi drops and you still get dist pulses, it still is on and if the dist pusle stops (in theory) the oil pressure switch will keep the pump on.
Of course without a ref pulse you'll have no spark to light it.
Jp

 

Heres the new one. Hope this is the right one. I looked at the engine & is pretty easy to find, If you stand on the drivers side & look between the back of the engine & the firewall you will see it next to the distributor & is all covered by the wires.

 

That isn't the oil pressure sender.

This is what is most likely broken:

 

The gold cylinder shaped item is an OIL PRESSURE SENDING UNIT. That is most likely what failed and has happend to my car and many others, plenty of times.


Unless I misunderstood what you were trying to say?

 

The black and silver part is the oil pressure switch that turns on the fuel pump.
Just to clarify.

 

Hmm... That's odd, because when I swapped the black and silver part my pressure reading was fine again. And when I went to autozone and asked for an "oil pressure sending unit," the black and silver part was what was sold to me.

 

Hmm is right, Thre are "some" pressure switches with the senders built in. (more pins in the connector)
I thought they were only used on LT-1s.
But I've been wrong before.
The pics represent what I have currently on my L98.

 

My "silver and black" piece has 3 pins, and based on the wiring diagram it seemed to be doing both jobs, but I can't verify that.

 

I talked to my friend Flyersman29 on the boards, he said that in '89 they only used the oil pressure sender switch ( the one down by the fuel pump) and they got rid of the big gold oil pressure sending unit.

I think thats why we're getting confused

 

I believe that it is not an oil sender problem but a problem with your main bearings. My guess is that your mains are worn and that the bottom end needs to be rebuilt. As a bandaid, use a heavier oil and change the oil filter to a Fram HP4 filter.

www.geocities.com/dzperf

 

i had a problem like that were my oil pressure was reading o psi, so i let it sit a while and then i was out to check out the situation when one of the bearings broke and the piston started to smack the heads

 

Sorry to cause the confusion, just trying to help.

 

The oil pressure sending unit changed depending on the year car you have. On the newer thirdgens (not sure what year the change was, but 89 sounds about right), the sending unit is no longer next to the distributor, but is located above the oil filter on the block. It will look like the black and silver piece pictured.

From what I have read (I havn't tried it myself), the fuel pump shutoff is a Myth. Several people on this board have unplugged the sender with the engine running, and the car continues to run fine. If it really would shut the engine off for low or no oil pressure, it would do it when the sender is disconnected.

As far as the bottom end needing a rebuild, it most likely doesn't. The vast majority of "weird" oil pressure readings are in fact bad senders. These things go bad way too often. They are under $20 from what I recall the last time mine went out. Last time mine went out, there was oil on the wire terminals when I unplugged the weatherpack connector. I cleaned it up, and installed the new one. Problem was fixed. By the way, mine was behaving the same way that yours was. It would read ok under acceleration, but would go down to zero when I came to a stop, or at idle.

 

92blue, according to my official GM repair manual (version 1988) it says that when the connector for the oil pressure sender (the litte gold cylinder next to the distributor) is disconnected, the gauge will read high pressure.

 

Problem solved! I installed the gold one and it fixed it.
Thanks to everyone for your help!

 

I know I'm reviving an old one, but I came across this thread on a search for a similar problem to the OP.

I have a Conv. 90RS, obviously, which has 166,000 miles on original motor. Only the tires/top/paint AND oil have been changed. Well, ok, the front suspension was changed a few years ago, as well as the spark plugs. Oh, and the AC was completely redone in 2005. Garage kept, this thing has really been pampered (as much as I can pamper a vehicle).

At any rate, now, when the car comes to a stop after getting close to 200*, the oil gauge goes down to about 5 and jumps around +/-2, but then goes to about 20 when I start going again. I put a quart of oil in since it was measuring slightly low, and this did help a little, the pressure still does the same thing, with the exception of topping out closer to 30 at cruising speed, but quickly decreases again when I let off the accelerator.

Well, I decided to pull the oil pressure sending unit to see if that's my problem. I had to jack the car up to be able to get under it as I couldn't get it off from the top side. Also, when I pulled the unit off, there was oil coming out of the part where the wires plugged into. I'm not an expert, but that doesn't seem normal. What do you guys think? I just finished pulling it out, so I'll have to wait till morning to get the replacement. Hopefully they have it at AutoZone!

Thanks to the previous posters for their guidance.

 

Well, it worked. Pressure goes right up to 30 without fluctuating. I'm a little concerned about the replacement sender tho. It looked nowhere near the quality of the original part - has way more plastic. I guess now I need to drain off a little of that oil I added.

Thanks again to the previous posters.

 

That's just a sign of the times. Cheap parts are cheaply made... in China I'm sure. SAD.

Glad you got it fixed. Low or no oil pressure can be a scary thing to see.

BUY AMERICAN!

 

Guess i'm reviving this thread again!

I have this problem too but I can't find a source for an oil pressure sender for a 91 Camaro Z28 305 TPI... Can anyone recommend a supplier? I need one that will accept non US credit cards.

UPDATE: I have found this part through a forum sponsor, TPI Parts,

http://tpiparts.net/inc/sdetail/500

From the sound of the description above, this looks to be the thing. Can anyone confirm before i order?

Thanks in advance

Bungle

 

Bump...anyone, anyone, Bueller.....

 

This is what you need to know,
Sensor connector:

1. One-wire is oil sending sensor for gauge. Thread must make contact with block to complete the circuit.
2. Two-wire sensor is a power switch which is in parallel with the fuel pump relay. It is isolated from ground - Sparky, ya know what happens when a hot wire touches ground!!
3. Three-wire sensor is gauge and switch. Guess they finally figured how to put Items 1 and 2 into one unit.

So which one(s) do you have?

My 2-cents on the quality issue.
If your an automobile maker and I'm your competition and also your parts supplier - things that make you go Hmmmm... what you gonna do? How many US suppliers actually make their own parts in the US? Don't answer that it's rhetorical.