Unusually high oil pressure

[AuroraGirl]

Does the '90 model year 5.7L still use the same fist-sized, green-stripe oil pressure sending unit down by the oil filter as the '88--'89?

They've got a known-high failure rate. They can read too low, they can read too high, and they can just read whatever they damn well please at any given moment.

If so, many parts-store computers list the WRONG sending unit for that application. What they list is too big, doesn't fit, and the heat shield has to be forced over the thing.

Left: Correct "green stripe" sending unit with heat shield. Right: Incorrect, too-big unit specified by NAPA and others.

You must be registered for see images attach

Correct P/Ns are
BWD S4320 It has a silver case, and green paint around the end with the electrical connector.

http://weblink.carquest.com/acl/?mfg...rtNumber=S4320

The NAPA / Echlin crossover from that number is OP6729. AutoZone sells it as PS150.

Best I can tell, they're all sourced from the same manufacturer.

If this is what you have, consider moving the wire up to the distributor area. Buy a 3-wire sensor, and the 3-wire pigtail. Take the two existing wires by the distributor, add the third one from the original sending unit, and use the more-reliable 3-wire switch/sending unit from a newer 5.7L.

BULLETIN NUMBER: 93-8C-28 SECTION: 8C NUMBER: 2 CORPORATE REFERENCE NUMBER: 268304 DATE: November 1992 SUBJECT: INCORRECT OR ERRATIC OIL PRESSURE READINGS (INSTALL NEW [1][2]OIL PRESSURE SENSOR) MODELS: 1990-93 ALL LIGHT DUTY MODELS Owners of some 1990-93 light duty trucks may comment that the oil pressure dash gauge reads high, has erratic movement or is inoperative. The internal resistance wire in the [1][2]oil pressure sensor may not be properly supported, resulting in an intermittent open condition. SERVICE PROCEDURE Check for normal causes of high oil pressure gage readings (high resistance or open circuit), such as a poor ground path caused by loose sensor mounting, oil cooler adapter loose, or poor electrical connections. If no cause can be found, replace the [1][2]oil pressure sensor following the procedure. 1. Disconnect the negative battery cable. 2. Remove the wiring harness connector from the [1][2]oil pressure sensor. 3. Remove the [1][2]oil pressure sensor. 4. Install the new [1][2]oil pressure sensor. 5. Connect the wiring harness connector to the [1][2]oil pressure sensor. 6. Connect the negative battery cable. PARTS INFORMATION You must be registered for see images attach New [1][2]Oil Pressure Sensor Part Numbers for the 1990-93 models Parts are currently available from GMSPO

 

[Jroctizzle]

I have not, no.

I’d do that just for good measure, they are around 8 bucks depending where you get them from. If it is contributing to pressure build up, super cheap fix, if not still super cheap and easy to replace.

 

[Schurkey]

BULLETIN NUMBER: 93-8C-28 DATE: November 1992 SUBJECT: INCORRECT OR ERRATIC OIL PRESSURE READINGS (INSTALL NEW [1][2]OIL PRESSURE SENSOR) MODELS: 1990-93 ALL LIGHT DUTY MODELS

I'd be happier if that bulletin went all the way back to '87 or '88 model years.

Even so, nice find. Thanks for posting!

 

[AuroraGirl]

I'd be happier if that bulletin went all the way back to '87 or '88 model years.

Even so, nice find. Thanks for posting!

I believe there is a bulletin for 1986-1989 (which covers the square bodies of that era as well) because I remember helping someone on the square body forum with it.

CHEVROLET NUMBER: 88-T-08 SECTION: 6D - Engine Electrical DATE: March, 1987 SUBJECT: LOW OIL PRESSURE READING MODELS: 1987 R/V, G, P AND 1988 C/K WITH LB4 (VIN CODE Z), L03 (VIN CODE H), L05 (VIN CODE K), L19 (VIN CODE N) TBI ENGINES Some 1987 R/V, G, P and 1988 C/K models with 4.3L, 5.0L, 5.7L and 7.4L engines with throttle body injection may have a low oil pressure reading at the gage. This condition may be caused by an incorrect oil pressure sender being installed in production. If this condition is encountered, it can be repaired by using a new oil pressure sender, P/N 10069218. The new design sender can be identified by a "60" that is stamped on the hex drive portion of the sender. For installation instructions, refer to the service procedure in Section 8C of the appropriate service manual. This condition was corrected in production beginning with the following VIN breakpoints: 1987 R/V Flint Line 1 GMC HF718914 Chevrolet HF368115 Line 2 GMC HF517180 Chevrolet HF136663 Janesville GMC HJ515257 Chevrolet HJ139069 St. Louis GMC HS515905 Chevrolet HS145384 1987 G Van Lordstown GMC 513772 Chevrolet 143213 Scarborough GMC 509369 Chevrolet 119458 1987 P Chassis Detroit GMC H3503077 Chevrolet H3315178 1988 C/K Pontiac GMC JE501049 Chevrolet JE103403 Ft Wayne GMC JZ500361 Chevrolet JZ103371 Oshawa GMC J1503576 Chevrolet J1110750

 

[AuroraGirl]

nothing i can find for 1989