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Anyone converted to a 3 wire oil pressure sender/fuel pump switch?

Discussion in 'The Garage' started by dyeager535, Nov 5, 2003.

  1. dyeager535

    dyeager535 1 ton status Premium Member

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    Just curious if anyone else has done this.

    Using (essentially) '88 Camaro TPI on the truck, and both a '91 Camaro and '91 454 3+3 use 3 wire senders/switches. However, those units aren't interchangeable, and I can't figure out why.

    Just looking for ideas/info on this, trying to figure out the best route. Would hate to buy one and have it not work, but with both being fuel injected V8's from the same year, you'd THINK they would be the same part!
     
  2. K5 NUTT

    K5 NUTT 1/2 ton status

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    What i can offer...in 90 the R/V trucks went to a 3 wire oil psi switch...basically incorperating the hot fuel handling - fuel pump relay bypass....gauge into one sender...89 down trucks use a seperate sender for the oil psi gauge...so one could wire it to be a 3 wire switch as long as the older style single sender for the gauge is hard wired into the new 3 wire pigtail...and one confirms the circuit is completed via the IC printed circuit...

    Unless one has access to special terminal crimpers for metri pak connectors...cheapest being MAC tools at $50 or so a pigtail from gm would run somewhere around $25 to pull it off without the special tools...just make sure you use heat shrink on all the butt connectors...and if a gm pigtail is aquired the heat shrink butts are in the bag.

    DW
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    I didn't bother checking for the 350 truck units, I figured they would likely all be the same though.

    Only thing that really throws me is why the units are different. From the online parts vendors pictures, the units ARE physically different between the car and truck, but not in the way I expected, which would have been for clearance. Even the V6 engines used a different part number, but having seen them, physically they look the same as the truck ones...again, I'm at a loss why GM needed a minimum of 3 different units to do the same thing.

    Since a '91 truck and car don't share the same unit, I'm leery of using one or the other for fear that the switch is somehow different in a way that will cause problems for me.

    As for the connector, I'll just grab one out of the wrecking yard and solder it to the existing leads (if the connector is the same)...one of the reasons for this is that the fuel pump switch wiring isn't long enough to reach the block in my setup, so I'd have to cut and splice anyway.

    Thanks for the additional info!
     
  4. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I might be able to tell you why two are different, one for a gauge and one for a light? The sender for a gauge is different than for a light.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Nah, both are for gauge applications.

    You could be onto something, perhaps a low oil pressure warning light in ADDITION to the gauge sender, but who knows.

    I'd like to use the truck one, because I know the gauge sender part is the same as mine, but why the heck would the fuel pump switch portion be different?

    It *may* be that the truck ones threaded into a different location. Can you or anyone with a later TBI truck comment on where theirs is located? Cars were above the oil filter, that fitting location is 1/4", the one next to the distributor is 1/8". IIRC, the '91 454 was mounted up front on the drivers side, down low.
     
  6. 90blzr

    90blzr 1/2 ton status

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    Correct, the 1991 454 3+3 is located on the drivers side up at the front bottom of the block.
    The 1991 only has that sedsor that I can see and that is the 3-wire type.

    My 1987 454 had a tee at the same location...but one have the 3 wire sender, and the other had a single wire going to it. The one with the single wire was a bigger silver sender. The one with the 3 wires going to it was a smaller black one...almost just like the one used on older chevy cars...just with 3 wires instead of one.

    We were just talking about this last night...why the two senders?? On the 1987, I undid the big silver one with the single wire going to it go install a mechanical oil pressure guage as I was trouble shooting some things, and the guage in the cab doesnt work with that sender undone.
    So what does the sender with the 3 wires do??? If it doesnt go to the guage? I assume one is the low pressue fuel pump shut off?? /forums/images/graemlins/thinking.gif The second is probably for the light *service engine soon* that comes on when your oil pressure drops down to low for comfort. The third wire...havent figured that one out yet /forums/images/graemlins/thinking.gif
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, on a car 3 wire setup, two wires are necessary for the oil pressure fuel pump switch. If I understand that setup right, two of the wires are necessary for the switch, since it either switches ground or voltage, and the third would be the actual gauge sender.

    I need to check my '88 Camaro wiring diagram, don't know if the fuel pump switch signals the ECM, or if it is wired in with the fuel pump relay only.

    You might be right on the '87 setup, all 3 wires are tied into the switching aspect, and on the later ones, they may have just integrated the sender as well, while letting the remaining two wires handle all switching necessary (idiot light, fuel pump switch)
     
  8. 90blzr

    90blzr 1/2 ton status

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    [ QUOTE ]
    Well, on a car 3 wire setup, two wires are necessary for the oil pressure fuel pump switch. If I understand that setup right, two of the wires are necessary for the switch, since it either switches ground or voltage, and the third would be the actual gauge sender.



    [/ QUOTE ]

    So if two wires are needed for the fuel pump switch...then the other must be for the 'service engine light' that comes on for low pressure. Non of the wires must go to the actual guage itself. As I said, with the secondary sender unplugged, the guage doesnt read...so that sensore must be soley for the guage.

    Like you said, they must have integrated all of the features into the 3 wire set up on the later models. /forums/images/graemlins/thinking.gif
     

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