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Hey engine guys...temp sensor question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by oh-zj-io, Apr 1, 2007.

  1. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    I just bought an 85 K5 from a girl for very little money. She did run it in the mud a few times so she wasn't just a poser. Anyway, she said that she was told that the engine and tranny had been changed before she got it and that she was told it was a 350. But when she purchased 'some part' for it she had to get a 305 part. So she isn't sure which it has. I'm not a long time Chevy guy and haven't done any engine work on them so I have no idea either. This is just my 2nd K5 and I haven't had the first one long.

    Anyway, the temperature guage doesn't work. I thought the sensor was supposed to be on the front of the intake manifold. I see no sensor anywhere on the manifold and I don't see the wiring and connector anywhere either.

    To complicate it a little, It has an Edelbrock manifold and covers on it rather than stock. I don't know the year of the engine nor the exact size. (It IS an 8 though...;) )

    Any thoughts or ideas? I can always do the new wiring, but, where the heck is the sensor to connect it to???? Or maybe, where SHOULD the sensor be???

    Thanks,
    Al
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Temp sensor is in the driver side cylinder head. The wire leading to it is a single usually green wire.
     
  3. dasanii19

    dasanii19 1/2 ton status

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    Sorta off subject.. Where can I get a replacment temp wire? Do I make it? or can I buy one to just plug right in?
     
  4. Currank5

    Currank5 1/2 ton status

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    Umm... you can buy a new piece of wire and splice it in. Buy a spool of wire from any hardware store, and some connectors to attach the cut wires.
     
  5. oh-zj-io

    oh-zj-io Registered Member

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    Hey!

    OK, I see the sensor on the driver side cylinder head and it has a green wire on it. This green wire, along with two other green wires (one attached to the air conditioning pump and the other somewhere farther down the front of the engine), go together into a wrap and the three of them plug into a 3 prong plug attached to the firewall directly above the distributor. The wires from the plug go along the firewall to the passenger side and then through the firewall an inch from the heater hoses.

    Does this make sense? Does it then go back across in the dash to the guage? Remember, someone changed the engine. I just mention this in case there is some reason to think it's screwy.

    I unplugged the wire attached to the sensor and the truck wouldn't start. I reattached it and it turned right over and started.

    If this IS the sensor and the sensor wire and it does run to something on the passenger side THEN to the guage...do you know what it runs to and then continue?

    Remember, the guage doesn't work. I would assume that if the sensor was bad then the engine starting problem would occur whether the wire was plugged in or not. Right, wrong, or not even close?

    Is my problem more likely the guage, the wiring to the guage, or the sensor? Heck, the wire may not be connected from wherever after it enters through the firewall to the guage. Is it still a green wire that attaches to the guage? I couldn't see or feel any connector on the back of the guage from under the dash so again I assume it connects inside the dash guage pod. Am I way off again? Or do I need to pull the instrument panel to check?

    I know. lots of questions, but, I'd really rather have a working temp guage than take a chance on overheating this thing.

    Thanks for your response and thanks in advance for any continuing help!!!

    Al
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Is this a computer controlled carb or TBI swap?

    Mine ('86 body) did not have the goofy temp sensor wiring you mention. I'm not aware of any application that the gauge wire was used to affect how the engine ran, so I suspect someone has butchered it up. Check that the plugs and what not are stock. It's very easy to see, usually mismatched screws, badly drilled holes, dents, inline connnectors, etc.

    Perhaps it's something to do with computer controlled carbs, or electronic spark control, but you'd have a distributor that wasn't "normal", it would have an extra wiring connector.

    If it's none of the above, you will have to figure out why disconnecting a wire that should run directly to the gauge cluster (no splices) is preventing your engine from starting.

    The wire enters the back of the cluster near the speedometer cable IIRC, and is probably the same green color there.
     
  7. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There should only be one green wire on the sensor and it should have nothing to do with the engine starting and running. From what you described i'm guessing there IS only one wire on the sensor but other wires that all go through the same convoluted tubing. Sounds like someone has messed with it and you're going to need to do some searching.

    Try grounding the green wire from the sensor with the key on and look to see if the gauge pegs HOT. If the gauge pegs hot then the gauge is good and the sensor is bad.
     
  8. dasanii19

    dasanii19 1/2 ton status

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    Just thought id ask before I started fiddling with it. Thanks
     

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