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Thread: Coolant sensor woes. '91 5.7 TBI

  1. #1
    Fuel Injected! pma4x4's Avatar
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    Coolant sensor woes. '91 5.7 TBI

    So I found out the coolant sensor on top by the thermostat housing is bad via a ohms test. I have a copy of ALLDATA and I then come across a connector image. It shows (#3) the one on top everyone knows about and its called "coolant temperature sensor". the other (#19) is called "Engine coolant Sensor".

    I can not find a diagram of BOTH circuits. only the one on top. If there are two I want to verify the other is functioning as well. My gauge in cab has been showing cold for some time. Like I said the sensor on top is in fact bad Ohms are all over the place and the engines runs like crap when not plugged in.

    I just came across this exploded connector view a little bit ago and I know there is a sensor there as I just saw it when I was testing today. Its between #1 and #2 cylinder and is a single green wire. Is the single wire sensor (#19) be the gauge unit? and the #3 on top just for the ECM? This is what I am starting to getting out of it. Any light shed on this would be great.

    This whole thing started because engine seemed to be running cold a lot lately and mpg is down, found sendor on top bad now wanting to test or replace other unit (if it is that). Going to be doing a new thermostat as as well and checking clutch on fan.

    Capture 1.JPG

    Capture 2.JPG



    Current: '91 1500 Suburban (3rd owner), 350 TBI, 700R4

    TBI system: RV Morse Bored TB - Matched FIs - Adjust. fuel psi regulator - Injector pod spacer - RV Morse Powerplate - Hypertech "salad bowl"

    Full write-up here

    Follow the build here



  2. #2
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    A quick search on the AutoZone repair guide wiring diagrams show the two circuits. Your assumptions for the location and use of the two component appear to be correct.

  3. #3
    Fuel Injected!
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    On my 94 TBI 350 the sensor for the temperature gauge only is the one in the head between cylinders 1 & 3.
    The sensor up on the intake manifold lets the PCM know what the engine temperature is, when you unplug that sensor it sets a fault code and the engine goes into limp home mode (and runs rough).
    From memory the sensors have different part numbers and a different number of pins.

  4. #4
    Fuel Injected!
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    My 94 tbi 454 is the same as yours.
    6395, BHDF, 7.4 BBC lightly modded now 6395 BMHM back to BHDF

  5. #5
    Fuel Injected! pma4x4's Avatar
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    ok so I am right that the sensor on the left head is for the gauge. Thanks for verifying guys

    Would anyone know if testing the ohm is the same as on the ECM sensor?



    Current: '91 1500 Suburban (3rd owner), 350 TBI, 700R4

    TBI system: RV Morse Bored TB - Matched FIs - Adjust. fuel psi regulator - Injector pod spacer - RV Morse Powerplate - Hypertech "salad bowl"

    Full write-up here

    Follow the build here



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