New Oil Pump, Same Low Pressure

[Jerrys1990]

PlayingwithTBI beat me to a couple of crucial points.

The sending unit that drives the gauge on the instrument cluster is a high-failure item. They can cause a too-high oil pressure reading, a too-low oil pressure reading, or just plain too-variable readings.

Many "computerized" parts catalogs list the WRONG sending unit for the '88--'89 trucks. The incorrect replacement is too damn big. The heat shield has to be forced over it, which means the heat shield is usually left off. It's a mess.

I put a big, long thread about this on another forum. I'm too lazy to re-post it all here. Problem is, that other forum has been "down" long enough that I wonder if they pulled the plug. All the part numbers and prices were in that thread, and I didn't have it stored on my computer.

Anyway, you're looking for a sending unit spaced out from the oil filter area by a brass ~80-degree elbow. The sending unit should have green paint on the wrenching surface. This sending unit is sold under various part numbers by all the usual parts stores--O'Reillys, Advance, AutoZone, NAPA--but so far as I can tell it's made by one company in Taiwan and then re-boxed by everyone else.


OP6649 is the WRONG sending unit.

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The 90-degree elbow and wrong sending unit still does not fit. It just interferes somewhere else. I tried everything to get that sending unit to work, and nothing helped.

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I'll re-check that other forum in a few days--please remind me--and if it comes back to life, maybe I'll work up the ambition to move that info here.

Also...I'm "done" with normal SBC oil pumps. I'm moving to the M99HV-S "big block" oil pump kit from Melling. Bolts to the rear cap exactly like a small-block pump, requires some (easy) trimming/modification of the windage tray on our engines, and comes with an acceptable pickup tube/screen for stock pans.
www.summitracing.com/parts/mel-m99hvs

Melling M-99HV-S Melling High-Volume Oil Pumps | Summit Racing

Free Shipping - Melling High-Volume Oil Pumps with qualifying orders of $109. Shop Oil Pumps at Summit Racing.

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Does this apply to 1990 trucks too? My oil pressure gauge bounces around all over and I'm thinking of testing and replacing the sender if necessary.

 

[Schurkey]

Does this apply to 1990 trucks too? My oil pressure gauge bounces around all over and I'm thinking of testing and replacing the sender if necessary.

Is your oil pressure sending unit located just above the oil filter, and does it have a green stripe at the wrenching surface?

 

[Jerrys1990]

Is your oil pressure sending unit located just above the oil filter, and does it have a green stripe at the wrenching surface?

Not sure yet, haven't looked. Was asking since 88-95 TBI's are usually similar. Next time I get up under it I'll see what it has.

 

[Schurkey]

I know '88 and '89 (and, I think the '87 squarebodies) used the high-failure sending unit. No idea when that changed, but it did change prior to the '96 Vortec engines.

 

[Jerrys1990]

I know '88 and '89 (and, I think the '87 squarebodies) used the high-failure sending unit. No idea when that changed, but it did change prior to the '96 Vortec engines.

I've been reading that 1990 was first year where the fuel pump/sending unit was combined in the switch by the distributor on the china rail. Now that I think about it, I don't remember seeing the high failure sending unit by my oil filter....