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Discussion Starter · #1 ·
I have a 89 W350 and it doesn't want to start when cold (-32). The wait to start light doesn't come on and that are wires unpluged from the engine in front of the starter area. Looks like someone remove/disabled or the PCM is shot. If I jump one of the solenoids on the left fender for about 5-8 seconds the engine starts well. Did anyone ever put a manual control for the intake heater? I know people that have installed them on 6.2 glow plugs and also people that have melted the glow plugs in the block. Can the intake heaters be damaged easily ? Is there any good way to fix this without a lot of $$$ ?
 

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I'm running a ford starter relay to control the power to the grid heater on my 4bt. I have the same heater that the 89-93 trucks have. Yes, if you forget to turn the heater off, you can burn it out. I have a light that comes on whenever the button for the heating grid is depressed. That way I don't forget.
 

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Discussion Starter · #4 ·
I was hoping there was a factory intake manifold temp sensor that I could wired in series with the momentary switch (that would override my command), to make it foolproof.
Is there anywhere I can find a wiring skizmatic?

How long can you hold the button on before thermonuclearer meltdown of the grid ?
 

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i have mine on a switch, when its cold out -30 and below, ill keep them on for 45 seconds, off for about 15, on for about 30 and then fire it up.
usually fires right off plugged in or not
 

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45 seconds? that seems very long. the max runtime for the heaters is 15 to 20 seconds when their operated by the pcm. the service manual also reommends not cycling the heaters multiple times.

Either way, 20 seconds shold be plenty.
 

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on this same subject why is there two relays and two heaters on my 89? according to my wiring schematic they are each controlled seperately by the computer ( they both show comon power but the computer grounds them seperately )
 

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ill have to find it, but i had the factory run cycle times on them for different temperatures. it was 45 for below -30 if i remember right. its been working good so far.
 

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the factory manual only goes down to -15f, and it reommends 20 seonds.

if longer is necissary for temps as low as -30, i wouldnt know, im just saying what the book says. the coldest ive ever seen is -3 degreesf.
 

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i had a old toyota diesel that the auto controled system was shot on. i just installed a spring loaded push button so i wouldnt accidentaly leave the switch on. i ran the the glow plugs through a solenoid. it worked great and was a easy fix. just figure out how long the it is suposed to cycle for and count it out while your holding it down.

fool proof easy fix would do the same if i ever had any problems with this truck.
 

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on this same subject why is there two relays and two heaters on my 89? according to my wiring schematic they are each controlled seperately by the computer ( they both show comon power but the computer grounds them seperately )
i may be wrong but i think there is 2 defferint heaters in the same block under the air horn. one is 75 amp draw and the other is 100 amp draw. if im wrong correct me but thats what i remember from what i heard.
 

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i may be wrong but i think there is 2 defferint heaters in the same block under the air horn. one is 75 amp draw and the other is 100 amp draw. if im wrong correct me but thats what i remember from what i heard.
hmm ii wonder why the two different sizes ?? im guessing there is a reason theycan power them seperately
 

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from what i was told the computer decides how hot (which amp heater) and how long to hold the heaters on by what the sensor tells the computer. i dont know if its right thats what i was told. it makes sence to me.
 

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There is no pcm on an 89. The heater control is a stand alone unit mounted on the firewall under the master cylinder. There is a temp sensor in the manifold that changes resistance with temp. Mine was behaving just like yours. I took the sensor out and checked it at different temps and it was ok. Next I took the factory connections apart and cleaned them up. When I put it back together it worked as it should. Oh yeah, I also checked the heater relays for continuity when they were energized. They checked out ok. So for no money, the heaters are working. You will also have to check continuity through the grids themselves.
 

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the service manual also reommends not cycling the heaters multiple times.
id like to hear peoples opinions on this. i was reading how people cycle them 2 or 3 times to get the temp up and to get the battery warmed up a little before the alternator starts charging. I usually do mine 2 times before i start it in the cold but if it might do more harm than good i would like to know.
 

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ok one more question, does the pcm cycle if they ignition is off? i start my truck and take the keys with me because i am in a bad neighborhood.
 

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no. it cycles once when the key is first turned on. thats the wait to start light. it cycles 2 more times i think when its running.
 
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