Oil Pressure Gauge and Sensor(s)

[GeoMotive]

Hi all,

I took my '89 G20 to a local shop for installation of a new engine and transmission as part of my planned full restoration of the van, which I inherited from my dad after the anguish of losing him to cancer. They up and shoved in a Jasper engine and transmission (the engine still leaking oil after three returns to the shop to correct it, and the transmission hard shifting into third despite another prior return to correct it-- But all of that is another matter), and now the oil pressure gauge is jumping all over the place. It'll show barely above zero at idle, jump to pegged upon launch/acceleration, and jump all over the place during sustained driving. The shop that did the engine/transmission work claims it's the gauge that's at fault, but I had my original gauge cluster fully restored prior to the engine install, and it worked fine with the original engine before this job was done.

The shop says they called Jasper to learn more about the oil pressure system, because they couldn't figure out what the cause was, and Jasper said there are two (2) oil pressure sensors on this engine (which is an identical TBI 350 to the original). Is that correct? TWO oil pressure sensors on these engines? And does anyone by chance have a part number or good online source to order new sensor(s) if I cannot find any other cause? I'm done dealing with these idiots, and will just address this myself. But I lamentably will have some degree of learning curve, as while I'm well experienced in working on my cars, until now I've only done so on Asian makes-- This is my first GM product. I've never heard of any engine utilizing more than one bloody oil pressure sensor, and thus felt it best to consult the greater knowledge of this board.

Greatly appreciate everyone's insight herewith. It's been a hard year, and I've been working on this G20 as a means of keeping a bit of dad with me as I do my best to carry on for him and our family. It's been incredibly frustrating how many shops outright won't work on vehicles this age, and then when you actually find one that will, they're totally incompetent. I mean abject dolts. Wish I had time to just do it all myself.

[MountainManJoe]

Welcome to the forum.

One is a pressure sensor for your gauge. The other is a fail safe switch that cuts off the fuel pump to save your engine from failure if the oil gets too low (and maybe turn on a light in your cluster).

Below is a flow chart for diagnosing gauge issues.
I believe the J-24538-A tool is basically just an adjustable resistor to send different voltages to the gauge. It can easily be improvised.
(https://ck5.com/forums/threads/infamous ... my.263131/)

I couldn't find an electrical schematic, but I'm sure there will be one in the Hanes repair manual.
The lack of familiarity with 30 year old vehicles is to be expected. There just aren't that many around any more.

Rockauto.com will have your sensor, but it's a matter of searching the right part number. I would try getting it off the part installed in the engine.
Looks like they're in the neighborhood of $40 so not too bad.

[MountainManJoe]

Here we go. Should be #7
007 Sensor, oil pressure indicator gage (60 psi)(1987-89)(acdelco #19244932)

[GeoMotive]

Greatly appreciate this insight. I've a genuine Chevy service manual on order for our G20, and should have a good source for reference, soon. Very interesting to learn about the secondary oil pressure sensor engaged for the purpose of saving the engine in the case of pressure loss. Thanks too for the sensor part number-- I'm not convinced they installed the correct pressure sensor to begin with, so didn't want to get it off of the part they installed directly. Good chance it's wrong, and that's why things are so squirrely with the gauge.

Our G20 is back at the original service shop (again) for now, I hope having the oil leak resolved once and for all. That, and a groaning AC compressor that they've also already replaced once under warranty. Either they're using cheap parts, or you just can't get quality anything anymore. It's been one problem after another with this vehicle, which has been very frustrating coming from one used to the reliability of Hondas and Toyotas. My dad got close to 240k on the original engine and transmission on this van before the engine finally developed rod knock, and I couldn't get 5 miles on the new engine without ceaseless leaks. And the new transmission hard shifts into 3rd, as well. I had to replace the rear end twice because the original replacement was incorrectly rebuilt. Wheel bearings failed on a trip after another shop had supposedly repacked them. Brakes ended up causing severe shudder at highway speeds because the shop forgot to bolt down the hardware. I swear this thing has been impossible. Absolute incompetence from every shop I've taken it to. Three different "ASE Certified" shops.