1990 Suburban oil pressure gauge only reads 30 PSI

[Bextreme04]

Thats interesting because my 1989 Suburban has the 3 pin combined pressure sensor/switch, but it is installed on the side of the block aft of the PS pump (and as far as I can tell that is the factory location since the wiring harness clearly routes to that location with no signs of modification). I wonder why they would have moved it for 1990.

The big block had it behind the PS pump on the side of the block in some years.

 

[GMPDO]

I bought my Burb with an oil pressure gauge basically stuck at 30 PSI. Disconnected oil pressure sender - Maxed out, indicating bad oil pressure sending unit. Reconnected - Back to 30 PSI. To make sure I also checked the gauge, it behaves as it should when tested outside.

So I replaced the sending unit and it came back to life, reading 0 when off and "something" when operating. I'm saying "something" because it shows too low in my opinion. But that's the topic for another thread as I'm not convinced if the one I got is the correct one for application.

For reference: 1990 Burb has a combined gauge-switch oil pressure sending unit, 3 prongs, hiding under distributor.

Have seen people question whether or not the sensor had good ground connection due to thread sealant. Something I'm gonna try related to that, is to run a dedicated ground wire from (-) battery and fasten it to case of oil sender with hose clamp. Already did that with O2 sensor.

Also, that ceramic film resistor on oil gauge may be flaky. I fixed my fuel gauge problem by "repairing" the resistor. You need those collars on ceramic piece to make good contact with the housing, so i reused it. scraped off the resistive material (gotta get it ALL off) between the terminals and soldered a pair of 180 ohm wire wound resistors across the ceramic collars for the nominal 90 ohms. my fuel gauge WAS reading low, now reads good. Same could apply to low oil gauge.

 

[YakkoWarner]

Have seen people question whether or not the sensor had good ground connection due to thread sealant. Something I'm gonna try related to that, is to run a dedicated ground wire from (-) battery and fasten it to case of oil sender with hose clamp. Already did that with O2 sensor.

Also, that ceramic film resistor on oil gauge may be flaky. I fixed my fuel gauge problem by "repairing" the resistor. You need those collars on ceramic piece to make good contact with the housing, so i reused it. scraped off the resistive material (gotta get it ALL off) between the terminals and soldered a pair of 180 ohm wire wound resistors across the ceramic collars for the nominal 90 ohms. my fuel gauge WAS reading low, now reads good. Same could apply to low oil gauge.

Did that dedicated ground on the O2 sensor make a notable difference? Asking because I get intermittant (come and go kind of randomly) lean code 44 errors on the SES light, but visually examining a pulled plug doesn't seem to indicate an overly lean burn. I've contemplated doing what you just described, but wasn't sure about if the wire would melt or the clamp would fail being right on an exhaust component.

 

[mibars]

Have seen people question whether or not the sensor had good ground connection due to thread sealant. Something I'm gonna try related to that, is to run a dedicated ground wire from (-) battery and fasten it to case of oil sender with hose clamp. Already did that with O2 sensor.

I didn't use any additional thread sealer other than a tiny amount of blue stuff that came on the threads of a new unit. I did remove my sending unit and checked it with air compressor, finding out it's quite inaccurate especially in low pressure region and more likely calibrated to 0-90 PSI instead of 0-60 PSI. More details in this thread: https://www.gmsquarebody.com/threads/oil-pressure-sending-unit-odd-readings-test-results.44011/
Afterwards I've installed it with a bit of PTFE tape, but I did check the resistance between the sensor and engine ground to be below 1 ohm.

Also, that ceramic film resistor on oil gauge may be flaky. I fixed my fuel gauge problem by "repairing" the resistor.

I'll check it again and also try to adjust resistance to match the sensor I have. But I'll probably wait until I'll be refurbishing dash or at least have more reasons to disassemble it.