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Truck just shuts off when turn on heater fan


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So driving the truck last night on Rt4. go to take the exit but decided to see turn the fan off and the truck just turned off. Wouldnt start up or anything. Get it towed home, and this afternoon it starts up fine. Start it up mess with the heat controls and same thing truck just shuts off. Any suggestions on where to start looking/problem solving? 1991 4.0L 5spd no a/c pioneer.

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Funny...

I just bought a 92XJ that has this same problem only the power dies when you turn on the Blower fan...

I have not looked into it since I am just parting it out anyways...

 

Should I figure something while tearing it apart I will let you know but my guess is the Computer...

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The title to your post says quote: " Truck just shuts off when turn on heater fan".

If you meant when you turned "ON" the fan, the truck dies, I'd suggest an electrical issue where a high current draw is killing the ignition. If this was the case then I'd look towards a resistance in the Batt/charging circuit caused by either dirty/bad battery cables or possibly bad grounds especially the block to chassis ground.

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All i see really when I looked under there were plastic covers. I took one of the covers with 2 screws holding it on off. Under it was a plug with 4-5 pins. Unplugged that and it still didnt start. Ever since I figured out the heater was causing it the 2nd time I turned it off it has not been able to start again. Last time it just randomly started working again. I also am not sure if it was from turning the blower fan on or off. When the first time it stalled on me I had the fan blowing, and I checked the heat to make sure it blew hot, then turned it off and the truck stopped. 2nd start up after towing it home I just slide the fan switch from off/on back off and the truck died out.

 

So I am still searching to answers but its hard to test whats causing it when i can't get it to start up again.

 

Sorry if i am confusing people with details or responses. Just trying to clarify more things. Going to search for some pics of this resistor to see what exactly I am looking for

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could be a short but I don't see how the controls on the heater would effect it. LIke I said i've had the truck for 2months no starting issues, and as soon as i Touch the fan from off/vent/etc i had the issues. I don't see any frayed wires and the grounding strap from the engine looks solid.

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I only mention it, because the heater fan and ignition are connected at that point. In my first 88 XJ, my ignition switch went out. Blower fan didn't work (truck still ran). I'm not electricity expert, but the blower motor may be pulling power from the ignition system when it's turned on, and killing the truck. :dunno:

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True, where do the two connect? Is it in the steering column or dash? Also wouldn't if it was drawing to much juice from the ignition to kill the truck, wouldn't when the fan was off it would be able to start? Its still raining hard out so I may have to wait till tomorrow for a serious amount of time. Anyone have the ignition or fan electrical wiring diagram anywhere. Also are the fans/heater or ignitions the same out of a Cherokee? If i need to pull parts out of my local yard?

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The ignition switch is at the base of the column.

 

You should be able to get parts from XJs with no problem.

 

It was just a passing thought, if you turn off the blower, then I'd imagine the truck would start if that was the issue. I'll have to let one of the electric gurus chime in and say if what I suggest is feasible or not.

 

Certainly can't hurt to at least take a look at the ignition switch though.

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unplugged the blower motor resistor and still no start.

 

All the fuses are good under the hood and dash. Battery is brand new, and the cables look solid. I will be going over the cables/block ground better after work tomorow if it ever stops raining.

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