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Engine Temperature Light

Discussion in '6.9L IH & 7.3L IDI Diesels' started by Whisp, Jul 2, 2019.

  1. Whisp

    Whisp Registered User

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    On my dash below my Glow Plug light is a Engine Temperature light. This rather warm morning when I went to start my old `86 the Engine Temp light came on and my Glow Plug light didn't. The engine refuses to start.

    Is there a over temp shut-off switch? I swear I heard the glow-plug solenoid engage.... however I didn't dig up the multi-meter to verify there was juice to the glow plugs.

    Could someone point me to an appropriate tread? I've had no luck searching.

    THANKS!
     
  2. franklin2

    franklin2 Full Access Member

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    Here's a diagram. I would go out and unplug the sensor in the driver's side head and see if the light goes out. If it does, inspect the wire closely and see if it has a bare spot touching the block.

    [​IMG]
     
  3. Whisp

    Whisp Registered User

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    Great diagram. I pulled both the Head and Block sending unit connectors a couple times, no obvious corrosion and the wire looks good. Now, the 'Engine Temp' light does not light when the key is turned on, (an improvement). Now it only lights when the engine starts to crank.

    The "Glow Plug" light doesn't illuminate and I guess I DID NOT hear the glow plug solenoid as reported before. (must have been smoking krak) The engine started once, but it's been in the 90s today. I tried to a second time with no joy.

    Guess it's time to start troubleshooting the Glow Plug module? (this march i installed new glow plugs, fuel return and cleaned injectors and she usually starts first crank or less)
     
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  4. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    Or just install a push button.
     
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  5. Selahdoor

    Selahdoor How can I help you, or make you laugh, today? Supporting Member

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    Unplug the temp sensors, and try to start the truck with them unplugged.
     
  6. franklin2

    franklin2 Full Access Member

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    If you look at the diagram, the light should light up when the key is in the crank position. That light gets 12v all the time on one side when the ignition is on. When the sensor reads a overtemp condition, it grounds the other side of the light and makes it come on. If you follow that branch off the wire that goes to a diode, and keep going, you will see it goes to the ignition switch and when in start, the ignition switch grounds the sensor wire on purpose to check the bulb each time you start the truck. You can see the water in fuel light is hooked in there and the brake warning switch to the left is too. All those lights should light up when cranking.
     
  7. jrollf

    jrollf Full Access Member

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    I think the lightbulb just went on for me (pun intended ) My temp light has not been coming on during cranking. As you describe it the flow of electricity reverses between test on crank and trigger by the temp switch... I replaced my dash bulbs with LEDs which are polarity sensitive... I'll try changing that one back to see if they start working again!

    My water in fuel light has the same problem.

    1993 F350 Crew Cab Dually
    XLT
    7.3 Factory IDIT w/Banks Sidewinder
    5spd Manual
     
  8. franklin2

    franklin2 Full Access Member

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    It doesn't change polarity. The ignition switch has at least 4 different sections to it. Most of them are switching battery power like you would expect, but the one section is by itself and the common to that switch section is ground. When the switch is sprung over to start, that section grounds anything hooked to it.

    So they take that section and ground the sensor circuits to make the lights come on briefly for a test.

    The diode you see in the diagram above is so the ignition switch can ground the overheat sensor wire to test the bulb, but if the overtemp sensor actually activates and grounds out in a overtemp condition, the diode will block it from grounding the water in fuel circuit.
     
  9. jrollf

    jrollf Full Access Member

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    Thanks for the clarification, I noticed my water in fuel light does come on for the test, so it is just my temperature light not illuminating... Need to slow down and troubleshoot it.

    1993 F350 Crew Cab Dually
    XLT
    7.3 Factory IDIT w/Banks Sidewinder
    5spd Manual
     
  10. Whisp

    Whisp Registered User

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    I haven't come up with a set of instructions for my 6.9, only newer 7.3. Suggestions?
     
  11. Whisp

    Whisp Registered User

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    Disconnecting the sensor wires made no difference. However, I did pull the harness from the controller unit, slimmed it with dielectric compound. Now the Glowplug light comes on when I turn the ignition on, however it doesn't seem to actually be heating the glow plugs. *note all glowplugs (motorcraft/german) were installed about a dozen starts ago.
     
    Last edited: Jul 8, 2019
  12. IDIBRONCO

    IDIBRONCO IDIBRONCO

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    It's pretty easy on these trucks. On the passenger's side fender id the glow plug relay. There's a small purple wire that has a push on type of connector. cut the wire leaving the end. Splice into that with the power from your push button. Keep it plugged in on the factory location. That's all that's required. You don't even need to have the solenoid on the back of the head plugged in.
     
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  13. Whisp

    Whisp Registered User

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    Thanks! I was hoping that was the answer, but as usual I over-think a problems. Do'oh! Lord Willing, I'll post results later today. Oooh, SQUIRREL!
     
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  14. Whisp

    Whisp Registered User

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    Ok, here goes.
    I have tried several different solutions on the glow plug solenoid each one more basic. I'm down to shorting the control lead stud directly to the battery, via double-ought wire.

    I bypassed the QD connector and crimped, soldered, & double shrink tube'd the wires. (took that variable out of the equation)

    bypass-cropped.png

    When I jump the control lead directly on the glow plug solenoid (purple wire) to the hot on one of the batteries, I can hear the solenoid engage, however, the voltage measured with a multi-meter from the glow plug lead is ~0.6 volts.

    Got a new solenoid from local Irish sounding parts store for only 2 bucks more then that famous cartoon rock band commercial online store. Now all works as it should! I'll be!

    Update: The truck ran about 1 mile and died straight away, no juice at all. After banging my head a bit on the fender, to no avail, I re-seated QD plug and she fired up. Needless to say that rest of the wires in that plug will look like their big brothers here, quite soon. Did I mention I hate QD plugs.
     
  15. Cubey

    Cubey Full Access Member

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    Hm, so the 6.9 (except 87 6.9 with the 7.3 style setup) need positive for the push button, unlike 87 6.9/all 7.3s that need ground? Good to know. I might get around to that mod myself.
     

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