Chevy K5 oil pressure sending unit help.

[Jake_C_]

I have a question about my oil pressure sending unit, I have reason to believe it’s faulty, the gauge goes to 15 when the truck is started and then stays there and never budges no matter what, it does go back to zero when the truck is turned off however. It’s possible I have low oil pressure but the truck runs fine so it seems like that’s not the case. I decided to replace to sending unit and since my blazer is carbureted I expected it to look like this:
It doesn’t though it looks like this one:

I was under the impression this smaller one was for instrument panels with the dummy lights and the bigger one was for clusters with the gauges. Am I wrong in this? Here are pictures of what mine looks like in the truck although you can’t see much: (this is located behind and to the drivers side of the distributer)


Any information on this is appreciated, thanks in advance. Also what in the world is this?:
And why isn’t that rod connected to something? Thanks guys.

 

[MEMO43]

What year is your rig,
my 83 has the sending unit behind the distributor.
The pic you are showing looks like it is connected to the Dizzy in which case it would be for the Spark Control.
As for the dummy light look for a connection near the oil filter, that is/ should be for the low oil pressure warning light
The other pic with the Pod and the bracket hanging off seems to be for the Cruise Control.
the first image you showed seems to be the correct one the one with the blade style connector.
Can you verify the gauge is working properly.

 

[Jake_C_]

What year is your rig,
my 83 has the sending unit behind the distributor.
The pic you are showing looks like it is connected to the Dizzy in which case it would be for the Spark Control.
As for the dummy light look for a connection near the oil filter, that is/ should be for the low oil pressure warning light
The other pic with the Pod and the bracket hanging off seems to be for the Cruise Control.
the first image you showed seems to be the correct one the one with the blade style connector.
Can you verify the gauge is working properly.

It’s not connected to the distributor, it has a 90 degree adapter that goes straight down into the block, I can’t get a picture of that part there’s too much junk in the way, I’ll take the air filter off when I get home and try to get better pictures. I guess I’ll have to test the gauge to see if it works right but like I said it does move just not like it’s supposed to. Thanks for the info about the cruise control I’ll be removing that junk. My blazer is an 88 which originally was fuel injected but the previous owner put in a carbureted motor, I was certain the carbureted motors had that canister looking oil pressure sending unit but mine doesn’t so I'm wondering if someone put in the wrong one. I might have to swap out the connector and get the right sending unit. I’ll also look into the other pressure sensor near the oil filter.

 

[6872xtc]

That is the correct style of sender for a TBI equipped one. It should have 3 terminals as it also helps control the fuel pump in the tank.
One of the wires in that plug will operate the gauge, but I don't remember what color it is. You can test the gauge by grounding the wire for it as the sender plug. Don't ground the positive wire for the fuel pump control..
And the rod off of the cruise control pod was originally hooked to a stud on the throttle lever.

 

[Jake_C_]

That is the correct style of sender for a TBI equipped one. It should have 3 terminals as it also helps control the fuel pump in the tank.
One of the wires in that plug will operate the gauge, but I don't remember what color it is. You can test the gauge by grounding the wire for it as the sender plug. Don't ground the positive wire for the fuel pump control..
And the rod off of the cruise control pod was originally hooked to a stud on the throttle lever.

Great info, thank you. I figured the rod for the cruise control went to the throttle body because of where it was located but I didn’t know it was cruise control. So then Is that sensor necessary or could I replace it with the correct one? it sounds like I can’t. Also what should I expect the gauge to do when I ground it?

 

[diesel4me]

You'll likely have to get the engine code off the block and look up what year engine you have,then order a sending unit for that year vehicle,and you will likely need to know if it has a 0-60 psi or a 0-80 psi gauge,to get the one that'll match up to the gauge..

One for an idiot light will be different,it'll be a lot smaller,and wont work with a gauge,its made to only turn the light on when pressure is really low or zero--gauge sending units need a variable resistance,while the idiot light ones are just an on-off switch--the ones for a gauge usually are a fairly large bell shaped unit..

Some newer trucks with computers might have two oil sending units--one behind the distributor,and another down near the oil filter--I think the one behind the distributor is for the oil pressure gauge or idiot light,the other down lower has something to do with the computer..

 

[Jake_C_]

You'll likely have to get the engine code off the block and look up what year engine you have,then order a sending unit for that year vehicle,and you will likely need to know if it has a 0-60 psi or a 0-80 psi gauge,to get the one that'll match up to the gauge..

One for an idiot light will be different,it'll be a lot smaller,and wont work with a gauge,its made to only turn the light on when pressure is really low or zero--gauge sending units need a variable resistance,while the idiot light ones are just an on-off switch--the ones for a gauge usually are a fairly large bell shaped unit..

Some newer trucks with computers might have two oil sending units--one behind the distributor,and another down near the oil filter--I think the one behind the distributor is for the oil pressure gauge or idiot light,the other down lower has something to do with the computer..

Right, that’s what I thought about the idiot light and gauge sensors. Seeing as mine is the small kind I figured it was for the idiot light and must be the wrong one but I think it’s the one for the tbi motors. Either way I don’t think it works for me. so the question is what are the other two wires for, if they control the fuel pump then is that just a ground for them? If I can separate them from the gauge wire and put in the single wire sending unit then it should work. I just have to figure out what to do with the other two.

 

[diesel4me]

I'm not much help on anything with EFI, I have only owned older trucks with carbs...so I cant tell you what to do about the leftover wires,or if they do run the fuel pump (I suspect they do,I think they kill the pump if it loses oil pressure ?--but again,I'm not familiar with EFI engines)..someone else here will probably know..

If you need a sending unit for a gauge with only one wire,there is likely one in the 1970's vintage that will work,you will have to match it to the gauge as noted above...my 6.2 diesel has a 0-80 psi gauge and one wire on the large bell shaped sending unit--maybe one of those would work if you have a 0-80 psi gauge--may need to adapt the threads though--I know small blocks have 1/8" NPT threads,but the diesel sender might be 1/4" or even metric..

 

[Jake_C_]

I'm not much help on anything with EFI, I have only owned older trucks with carbs...so I cant tell you what to do about the leftover wires,or if they do run the fuel pump (I suspect they do,I think they kill the pump if it loses oil pressure ?--but again,I'm not familiar with EFI engines)..someone else here will probably know..

If you need a sending unit for a gauge with only one wire,there is likely one in the 1970's vintage that will work,you will have to match it to the gauge as noted above...my 6.2 diesel has a 0-80 psi gauge and one wire on the large bell shaped sending unit--maybe one of those would work if you have a 0-80 psi gauge--may need to adapt the threads though--I know small blocks have 1/8" NPT threads,but the diesel sender might be 1/4" or even metric..

I definitely can get the single wire, bell shaped, sender. I guess the only problem now is what to do with the other two wires.

 

[Wes Harden]

Does it actually have 3 wires? It may only have 1 wire.
If you have 1 wire, unplugged the guage will read low and grounded should show max. If you put a test light between wire and ground the guage will read some where in between.
The correct sender could look like the silver with black plastic sender linked above.
Do you have an electric fuel pump?
On a 3 wire sender 1 is guage, the other 2 are for electric fuel pump.
The sender has a switch, oil pressure closes and powers the pump after the engine starts. Thou this option is for TBI engines.

 

[Jake_C_]

Does it actually have 3 wires? It may only have 1 wire.
If you have 1 wire, unplugged the guage will read low and grounded should show max. If you put a test light between wire and ground the guage will read some where in between.
The correct sender could look like the silver with black plastic sender linked above.
Do you have an electric fuel pump?
On a 3 wire sender 1 is guage, the other 2 are for electric fuel pump.
The sender has a switch, oil pressure closes and powers the pump after the engine starts. Thou this option is for TBI engines.

Good questions, I’m going to dive into it tonight to look, my best guess is that if it does have 3 wires the two for the fuel pump are no longer connected because I no longer have a computer. Here’s a diagram I found for the fuel pump:
You can see some wires go to the ecm

 

[Wes Harden]

The computer command control carburetor cars/trucks had mechanical fuel pumps.
The guage in your dash is calibrated to use a certain sender. So if you use an older unit the guage will read differently. It could work as long as you know what you are seeing.
If oil pressure is in doubt use a mechanical guage to prove you have good oil pressure or not

 

[1-ton]

Since the TBI has been removed for a carburetor you could convert the oil pressure gauge set up to a mechanical direct feed oil pressure gauge. You will have to get at the TBI oil pressure sending unit and remove it, then get some brass fittings that will allow you to connect a mechanical direct feed oil pressure gauge to the engine block oil pressure port.

Those TBI oil pressure sending units and the engine block oil pressure port are a B!TCH to get at. You will have to remove the cruise control, and probably even the distributor, in order to get to it. I created a dual port brass fitting for my TBI small block 350 engine block oil pressure port so I can tap into it both a mechanical direct feed oil pressure gauge for trouble shooting, and the TBI oil pressure sending unit for my factory stock gauge.

 

[Jake_C_]

Ok I have a 0-60 gauge, the connector to the oil press sending unit has only 2 wires:
It looks like the two wires are orange and tan. Here’s a better picture of my sending unit:
From reading online it appears that the tan wire is for the gauge, if I ground it, the gauge should max out correct?

 

[Wes Harden]

I see pink for gauge and tan w/ white for fuel pump. but only 2 wires is messing with my knowledge. Now I am wondering if there isn't a seconded sender. Maybe by oil filter?

 

[Wes Harden]

I had 83 in my head for 1st post, 88 is totally different. So you have an electric fuel pump or mechanical? Also how does the distributor function w/o the computer?

 

[Wes Harden]

I wouldn't ground any wires just yet. This diagram matches what you have. If so the computer controls the gauge, or there is a second sender.

 

[6872xtc]

Yes, you should be able to ground the tan wire and peg the gauge. But as @Wes Harden said, tan with white is fuel pump control, and plain tan is oil gauge or light.

It surprised me that it only has 2 wires, but I was trying to remember what I saw on my '90, I didn't have a book to access while at work today. I looked at an '87 book tonight, which shows the 2 wire plug for the fuel pump but I couldn't find where the tan wire for the sender went. (Location) It only showed a sensor, but I couldn't determine if it was a separate one or what.
I am probably just not connecting the pages properly while sorting through applications and circuits,

 

[Jake_C_]

I had 83 in my head for 1st post, 88 is totally different. So you have an electric fuel pump or mechanical? Also how does the distributor function w/o the computer?

Yeah Idk I’m confused now. I removed the whole cruise control unit and I’m guessing there is more wiring I can clean up that no longer goes to my motor. As for the distributor I’m assuming it works from the engine cranking. I grounded the tan wire earlier and now my fuel pump isn’t coming on when I turn the key so I may have blown that fuse, hopefully that’s the case, now I have to find that fuse. I’ll have to take a closer look at that tan wire it might be tan and white, does that mean the orange one goes to the gauge? My temp gauge didn’t work either but the wire was all burnt and crispy so I fixed it and when grounded the temp gauge pegged so hopefully my sensor is still good, of corse now i can’t start it to check because of the fuel pump. Maybe I should get a new wiring harness for this thing it might clean a lot of stuff up.

 

[Jake_C_]

Yes, you should be able to ground the tan wire and peg the gauge. But as @Wes Harden said, tan with white is fuel pump control, and plain tan is oil gauge or light.

It surprised me that it only has 2 wires, but I was trying to remember what I saw on my '90, I didn't have a book to access while at work today. I looked at an '87 book tonight, which shows the 2 wire plug for the fuel pump but I couldn't find where the tan wire for the sender went. (Location) It only showed a sensor, but I couldn't determine if it was a separate one or what.
I am probably just not connecting the pages properly while sorting through applications and circuits,

Well if you find anything else let me know, the tan looking wire didn’t do it for me so maybe it’s not tan and instead it’s tan and white, I guess my next step is to check fuses and see what I can find out about another oil pressure sender