Dual Oil Pressure Senders

[JCampbell]

'84 1/2 ton, 305 (ccc). I have two oil pressure sending units. One, single-wire unit up top by the distributor, and one two-wire unit down by the oil filter. I'm assuming the single-wire unit is for the gauge, but what is the two-wire unit for?

[Jabes1]

Its for that mesh shirt.

[JCampbell]

[Rich84]

That's the oil pressure switch...It's a redundant circut that lets the fuel pump run when it senses oil pressure in case your relay for the fuel pump fails.

[manimal]

[geezer#99]

Not sure what the 2 wire one is for yet but it's not for a relay for the fuel pump. His 84 doesn't have a tbi or an electric fuel pump.
I suspect the one by the filter is tied into the electric choke. No oil pressure shuts off power to the choke, it closes, kills the motor. I had one on an 80 malibu.

[Rich84]

I think it's a TBI conversion..

[geezer#99]

Well that changes everything.
It must be for the flux capacitator!

[JCampbell]

It is a TBI conversion, but this is the original wiring for the truck, which had a CCC Quad.

Basically, I need to find a place to install the TBI oil pressure switch, and want to know if I can 86 the existing sending unit down by the filter and install the new unit in it's place.

[JCampbell]

Wonder if these two are related:

http://67-72chevytrucks.com/vboard/s...d.php?t=588046

[Rich84]

On my TPI both the switch and the gauge sending unit are together behind the distributer..There is a special fitting that recieves both..On mine the gauge is the single wire.

[hatzie]

Originally Posted by geezer#99

Not sure what the 2 wire one is for yet but it's not for a relay for the fuel pump. His 84 doesn't have a tbi or an electric fuel pump.
I suspect the one by the filter is tied into the electric choke. No oil pressure shuts off power to the choke, it closes, kills the motor. I had one on an 80 malibu.

Two wire is for the factory electric Choke up to 86.
On the 87-91 RV chassis it controls the TBI fuel pump.

[JCampbell]

So I can remove the two-wire sender and use the TBI fuel pump switch that I need, correct?

[PAWS 72]

I have been wondering also.

My son's 87 oil gauge has been acting up and I took the one off at the dist. housing and installed a aftermarket gauge and it seems like it takes a little longer to start. Should I put the regular oil pressure switch back in or does it hurt to run the aftermarket one.

It is a 87 with tbi.

[hatzie]

Originally Posted by JCampbell

So I can remove the two-wire sender and use the TBI fuel pump switch that I need, correct?

Should work. You can probably use the existing pressure switch unless the connector is wrong. It just closes the contacts when the pressure rises above the setpoint.

[hatzie]

Originally Posted by PAWS 72

I have been wondering also.

My son's 87 oil gauge has been acting up and I took the one off at the dist. housing and installed a aftermarket gauge and it seems like it takes a little longer to start. Should I put the regular oil pressure switch back in or does it hurt to run the aftermarket one.

It is a 87 with tbi.

This is the single wire gauge can? If so your longer startup isn't related.

I believe the TBI fuel pump circuit is setup to prime the lines when the key is first switched on and the oil pressure is zero. I'm not sure whether the ECU controls this or if there's a relay setup.

[Rich84]

You will only get longer startups if the fuel pump relay is not working..In which case it uses the circuit thru the oil pressure switch.

[PAWS 72]

The truck has a little cam and since I had to idle it up I'm assuming that may be the cause for the longer starts also.But the relay and pump are working. Correctly or not I dont know.I used the port at the dist. for the aftermarket gauge will that make any difference or do I need to go ahead and install a new switch in that port to weed out that problem?

I want to get the mechanicals right before I decide what and if I use any of it on my 82 3/4 ton.And then again my son may decide to keep and drive it and I get to keep the short bed I bought.

[hatzie]

Originally Posted by PAWS 72

The truck has a little cam and since I had to idle it up I'm assuming that may be the cause for the longer starts also.But the relay and pump are working. Correctly or not I dont know.I used the port at the dist. for the aftermarket gauge will that make any difference or do I need to go ahead and install a new switch in that port to weed out that problem?

I want to get the mechanicals right before I decide what and if I use any of it on my 82 3/4 ton.And then again my son may decide to keep and drive it and I get to keep the short bed I bought.

The oil gauge pressure sender is behind the distributor. Runs the gauge only nothing else. If you look at any of the 73-89 wiring diagrams you'll note the sender wire runs direct from sender to the gauge.

The oil pressure switch is down near the oil filter. This tells the TBI fuel pump relay and prolly the TBI ECU that the engine has oil pressure.

Look in my sig for 73-91 wiring diagrams and service manuals.

[PAWS 72]

Thanks. Hatzie I have already replaced that one also.