killerbean

Hey all, my oil pressure gauge goes as far as it can to the right whenever the car is running or when you turn the key to the run position.

I searched around on here and saw people with similar problems were saying it was likely the sending unit. I installed a new one and still have the exact same problem. Every time the key is turned or car is running the gauge is pegged past 60 psi. Even with the sensor unplugged. When you turn the car off and take the key out the gauge will slowly drop to 0 psi.

I was thinking it was maybe the gauge but the gauge goes up and down no problem. I would think a bad gauge would stay stuck at a certain pressure.

Any thoughts?
TIA

AlkyIROC

Do you have the correct sensor installed? There are 2 different types of sensors. One uses a variable resistor which will change with pressure to show on a gauge. The other is just an on/off switch to turn on a warning light.

Pressure stays high with sensor unplugged? Connect sensor wire to ground and recheck.

Thirdgen89GTA

iTrader: (5)

It's been a while, it's possible I flip-flopped this in my head. But The gauge works on resistance.

A grounded wire will put the needle at zero. A gauge with no ground will peg itself.

I remember there are two gauge's for birds, don't know about the Camaros. But there is a 60psi and 80psi gauge. Wrong sender = inaccurate readings.

killerbean

I have tried 3 sensor's now. This is the one I just put in.

The engine is a 5.7 out of a 1989 trans am. When the engine was in the 89 that gauge also showed max oil pressure. When I swapped the engine into my 88 I had to use the oil pressure sensor from the 5.0 that was originally in the 88 because the wiring harness from the 88 has 2 prongs where the one from the 89 has 3. The 2 prong sensor from the 5.0 also showed max oil pressure when put into the 5.7. I am not sure if it worked before because the 5.0 was seized. Finally I bought the one linked above and same result. Max oil pressure...
​​​​​

QwkTrip

iTrader: (22)

That's my memory too. Open circuit (no current flow) will peg gauge needle to the high side whenever voltage is applied to the gauge with key on.

+12V source is from the gauge.
Oil pressure sender makes electrical continuity to engine block by direct physical contact metal to metal.
And the circuit is completed by ground cables back to battery.

killerbean

I went to try to ground the connecter to see if the gauge dropped and there is no power at the connecter.

AlkyIROC

There shouldn't be any power at the connector. It's a grounding wire. The sensor provides ground through the internal resistor to activate the gauge. The gauge should have 2 readings. One with the wire disconnected (usually max high), and one with the wire connected to ground, zero pressure.

If the gauge doesn't change then you have a wiring problem.

If you want an accurate oil pressure reading, use a mechanical gauge however do not use the cheap plastic hose that comes in kits. Use copper line especially if the gauge is inside the car.

killerbean

Gotcha. I did ground the sensor wire and its still max pressure. Just wasnt sure if it was meant to have power at the sensor connecter.

Thirdgen89GTA

iTrader: (5)

What color is the wire and what year, make, model is your car.

The pinouts changed from year to year and are sometimes different between Camaro/Firebird/TBI/TPI/V6....etc.

Thirdgen89GTA

iTrader: (5)

C100 diagram that matches my 89 TA GTA says that E5 is the Tan wire.

sofakingdom

iTrader: (1)

The OP gauge is like several of the others. It has 2 coils; one always has 12V on one side and ground on the other (when the key is on, that is) arranged so that it pulls the pointer toward full-scale, and the other has 12V on one side and the sending unit on the other, pulling the pointer toward zero. The temp gauge is the exception: same principle, except the direction the 2 coils move the pointer, is the reverse of this. The resistance of the sending unit coils in the gauges is usually some tens of ohms, like between 50 and 200 or so, for the different gauges. Shorting the SU wire to ground should bring the gauge all the way to 0, so for example, if you put a OP sw SU for an idiot light into a gauge car, then the gauge will read full-scale when the switch is in the "happy" state, but read zero when in the "alarm" state. (the temp gauge logic is the opposite) The OP sending unit wire should "appear to" have 12V on it with the key on, when measured with a high-impedance voltmeter. If yours doesn't, then either the gauge is defective (rare but of course possible), or the circuit between the gauge and the SU lacks continuity (much more likely). Check the wire itself, especially at the SU connector, where it can break easily enough; C100; the "printed circuit" on the back of the dash; and the connector where the harness plugs into the dash.

killerbean

1988 trans am GTA TPI

Gauge goes to 60 psi

AlkyIROC

2 wire oil pressure sensor.

Use a paper clip, cotter pin etc and jump the 2 wires.
Jump each wire separately to ground.

Does the gauge still stay at 60 psi when anything is jumped?

If the tan wire is signal return to the gauge, the white wire is probably a ground circuit. You can resistance test the white wire to so if it goes to ground but if the gauge doesn't change when you ground the tan wire, I'd say it's broken somewhere. You can always backfeed a grounding wire into E5 to determine if the bad circuit is inside or outside the car.

killerbean

I did try to ground both the orange and tan wire using a test light and neither one of them dropped the gauge.

The only thing I managed to do is touch the test light to the headers and blow the 20 amp fuse next to the battery lol.

The other thing I tried was jumping the wires together and it sounded like something turned on. Not sure why the oil pressure sensor wires would do that. Seemed kinda weird to me.

Chris 84TA

on some vehicles gm uses the oil pressure sensor to turn on the fuel pump as a relay bypass. when it gets to 4psi oil pressure it kicks power to the fuel pump.

Thanks,
Chris

AlkyIROC

Sounds like you're checking the wrong oil pressure sensor. As mentioned above, that could be for electric fuel pump shutoff. Normal oil pressure sensors only use 1 wire.

Don't use a test light to ground a wire. The resistance in the bulb won't make it work right. If the light is LED, then it won't work at all.

Pressure sensors can be located down beside the oil filter or on top of the engine bellhousing sort of behind the distributor and driver side head.

killerbean

I'll have to try to ground it again not using the test light.

Are you saying there are two oil pressure sensors? When I had the engine out I don't remember there being any other connecters on the back. Just the two going into the distributor, the EGR, and the one that goes into the bottom of the plenum.

I thought the oil pressure sensor was the one right above the oil filter. That's where I installed the new sensor.
​​​​

AlkyIROC

As mentioned above, an on/off sensor can be used as a fuel pump shut off. It won't turn on the fuel pump until oil pressure is detected which is what a 2 wire sensor sounds like. A second variable resistance sensor is used for a gauge.

Plug your sensor back in and start the car. Once running, unplug the sensor and see if the engine shuts off for lack of fuel.

I'm looking through a local parts store catalog and it lists 2 sensors. One for a warning light, one for a gauge.

The gauge sensor has a large canister body and a single spade connector. Look behind the distributor.
GM part numbers can be
10007393
14036243
19244933
459417
459457

The plug you show in the picture is for the low oil pressure warning light. GM part number 25037045

killerbean

That's the back of the motor. I am not sure where it would be if it's behind the distributor.

I'll have to check if the car shuts off when I unplug the sensor above the filter when I get a chance.

ACebell

In the picture the port is blocked off by a brass fitting. To my understanding that is where your Oil Pressure Sender Switch would be located. Perhaps the old engine didn't have it either thus your gauge never has worked?

AlkyIROC

On the engine/dash harness in that general location, is there a spade connection?

sofakingdom

iTrader: (1)

The place for the OPSU is in the top of the block, same surface the intake manifold sits on, behind the intake, under the distributor. Has a square-head brass plug in it ATM.

killerbean

I'm pretty sure there is no connecter on the wiring harness for oil pressure sensor behind the distributor. When I pulled the previous motor I don't remember unplugging anything like that.

So if there is no sensor behind the distributor does the sensor above the oil filter control the oil pressure gauge or is that strictly for fuel shutoff in case of no oil pressure?

AlkyIROC

It sounds like the sensor by the oil filter is to turn on the warning light unless you can pinpoint what noise you hear when you jump the wires. You won't have a 2 wire sensor controlling an oil pressure gauge.

You have to be missing a harness wire somewhere.

Thirdgen89GTA

iTrader: (5)

On later cars it’s a 3 wire combo sender/sensor just above the oil filter to handle the low oil idiot light, fuel pump relay, and gauge.

at least that’s the way it was for my 89GTA originally.

I just use a single wire bell sender on the top of the block at the back of the intake with my LT1 swap.

killerbean

That would make sense because the motor is originally out of an 89 GTA and it had that 3 wire connecter. I had to swap it to a 2 wire connector to fit the 88 wiring harness.

​​​​

AlkyIROC

and now your oil pressure gauge doesn't work. Hmmm. Think you found the issue.

killerbean

Yup lol... I thought the 89 and 88 tpi were the same other than the cold start injectors which was not an issue I just did not plug them in. I did not realize some other thing were different like the throttle body and now oil pressue sensor. I am surprised the car has been running as good as it does other than when its cold it barley runs lol.

JoeJack

iTrader: (1)

Reviving this thread because I have a similar problem.

I swapped an 88 motor into an 89 and didn't realize the oil pressure sender was behind the distributor. There is pretty much no room to get to the little brass fitting unless I take the intake manifold off. So I was wondering if you could take the single tan wire that would go to the sender behind the distributor and extend it to connect into a 3 prong sender/switch that's above the oil filter like in an 89. Or does the gauge have to be match with the sending unit? In this situation I would be using the 88 gauge with the 89 3 prong sender/switch.

Just a thought I had. I'm hoping someone can tell me if this is stupid or not lol.

Thirdgen89GTA

iTrader: (5)

I have a single wire bell Seder for my 89. There is room.

its just a single wire guage. So as long as the resistance for min/max the it’s the same and the gauge doesn’t care.

JoeJack

iTrader: (1)

My current oil pressure switch is for an 88. It has 2 wires going into it, an orange and a tan with a white stripe.

I have a connecter for the 3 prong oil sensor/switch from an 89 wiring harness. It has an orange, tan with a white stripe, and a solid tan.

So are you saying if I cut the 2 prong 88 connector out and splice the 3 prong 89 connector in as long as the resistance on whatever sender/switch I buy correlates with the 88 gauge it should work as normal. If so is there any way to know what 3 prong oil sender/switch will work with the 88 gauge.