Oil Pressure Sending Unit

[dragginmetal]

1988 GMC 350 auto c1500 2wd
I pulled the '88 motor out and put a '92 in. On my '88 the sending unit is above the fuel filter. The '92 does Not have one here. Its a plug in that hole. Reading past post someone said the '88 has two sending units. One by the filter and by the distributor. The '92 only has the one by the distributor.
My question is where do i hook the wire that is hooked to the sending unit (by the fuel filter) on the '88 too, now that i have a '92 with only one sending unit. This seems to control my dash guage.
I tryed to take it off the '88 (sending unit by filter) and put it on the '92, but the hole in the '92 block seems smaller.....The sending unit by the distributor is the same on both motors. (both have 2 wires).
So how do i get my oil pressure gauge to work?.......Sorry for the long post, just trying to give all the details.....Hope all this makes since.




This is not on the '92.




This is the same on both motors.

[ChevLoRay]

If the later motor only has the one sending unit, could it be that the later unit does both functions, whereas the earlier motor has to have both? I don't have the answers, but hope someone will.

[dragginmetal]

ChevLoRay thats what i was thinking. Maybe the one unit on the '92 would be 3 wire and i could splice into it. But nope, thet are the same 2 wires and the same unit....Also the wire harness that came with the '92 is the same as the '88.(im useing the original w/harness that came in the truck('88)). The '92 has the wires for both units, but the one wire i need hooked up looks like it wasent in use on the '92.

[Boog]

On your 88 the unit by the distributor is for the oil pressure gauge. The one by the oil filter was discontinued a year or so later. Had to do with the fuel pump power circuit.
You should be able to take the brass threaded adapter down to a parts store and down size or upsize to fit the hole in the block so that secondary sender can be hooked back up.

[dragginmetal]

Boog, My gauge is not working, but the one by the distributor is pluged in. You think that unit might be bad?.....The one by the filter is unpluged, but the truck runs good. I would like to do away with the one by the filter if possable, but i will go to the parts store and take a look.

[ChevyTech]

The 1992s have a three wire sending unit by the distributor.
One is for the oil pressure gauge and two are for a fuel pump redundant circuit.

The 1988s have a two wire by the distributor and a one wire by the oil filter.
The one wire sender by the oil filter is for the oil pressure gauge, and the two wire sender by the distributor is for a fuel pump redundant circuit.

You can pick which way you want to go. You can use the 1988 setup with two sending units which will make it correct for the model year, which is what I would do. You could get a sending unit connector for a 1992 and wire it in and use one sender. Or you can leave them unplugged and see how lucky you are.

Be careful, the brass fittings break easily. Support them with a wrench.

[bwood]

You need to use the sensor from your 92 or get a new one. On the 88 trucks the one by the oil filter (looks about like a coke can) is actually for the gauge. The one next to the distributor is a switch (on/off only) that works with the fuel pump circuit. In 90 ( or somewhere in there) they did away with the switch and moved the sender up next to the distributor. Look into the harness for the 92, it should have 3 terminals.

[bwood]

ChevyTech got me, I need to type faster

[dragginmetal]

Im going to get a reducer for the brass fitting, and use the (coke can) unit on the '92. I will let y'all know how it works. .......BUT, since the '92 does not have the (coke can) unit. How did the guage work? You can see in the pics same unit(both have only 2 prongs), same w/harness (both have 2 wires).


Unit on '88

Unit on '92.....same on both.



'88 w/harness

'92 w/harness.....same on both.

[ChevyTech]

What was the 1992 engine in?

Did the 1992 vehicle have an oil pressure gauge?

[dragginmetal]

It came out of a stock 1992 gmc c1500 2wd. It came from a wecking yard. I watched as they pulled it out of the truck. I did not see it run, so cant say if guage worked on that truck. But that is the w/hareness, and the unit that was in that truck.

[ChevyTech]

I was fairly sure that the large can senders by the oil filter were not used as late as 1992 but I could be wrong.

I don’t have a 1992 schematic handy to look at.

The senders by the distributor that were also for the oil gauge were longer and larger then what is in your photos.

Look carefully at what is down by the oil filter and see if it is a broken off fitting. Maybe that is why it looks to small.

[bwood]

Originally Posted by dragginmetal

1988 GMC 350 auto c1500 2wd
I pulled the '88 motor out and put a '92 in.

I think I read your post wrong, I was thinking you had a 92 and you were putting a 88 engine in. I read it backwards, you are putting a 92 engine in your 88. You will need to install the sensors from the original 88 engine on the 92 engine. You will still need the "coke can" pressure sending unit for the gauge. Straighten me out if I still got the years/vehicles wrong.

[ChevyTech]

To be more clear, I agree with bwood.

Make the new engine match the way your 1988 was.

[ChevyTech]

1991 GM 8 cylinder Oil Pressure Sending Switch Location

Source:
http://autorepair.about.com/library/...bl283a-lib.htm


Here is the best photo I could find:

[dragginmetal]

Well post #16 and everybody is confused. Sorry abought that.
I was going back and forth, posting and working on the truck...I will make the new just like the old. Thanks for the replys.