Northup Posted July 12, 2010 Share Posted July 12, 2010 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. Link to comment Share on other sites More sharing options...
Jeepman Posted July 12, 2010 Share Posted July 12, 2010 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... Link to comment Share on other sites More sharing options...
Northup Posted July 13, 2010 Author Share Posted July 13, 2010 Ya, I was definitely thinking it was something electrical, but have no Idea where to look. I thought all the fans were vacuum operated switches. If anyone has any other Idea it would be appreciated. Link to comment Share on other sites More sharing options...
Automan2164 Posted July 13, 2010 Share Posted July 13, 2010 The blend door and such is vacuum operated... Not the fan. The fan is all electrical. Does it still do it if you unplug the blower motor resistor? Rob L. Link to comment Share on other sites More sharing options...
Northup Posted July 13, 2010 Author Share Posted July 13, 2010 no Idea. Have not tried to really work on it yet. Where is that resistor at? Under the dash by the fuse block or somewhere else? Link to comment Share on other sites More sharing options...
64 Cheyenne Posted July 13, 2010 Share Posted July 13, 2010 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. Link to comment Share on other sites More sharing options...
kyleag89 Posted July 13, 2010 Share Posted July 13, 2010 The resistor is located on the pass. side. It has 2 screws holding it and it will be right in front of your face when you look under the dash. Link to comment Share on other sites More sharing options...
Northup Posted July 13, 2010 Author Share Posted July 13, 2010 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 Link to comment Share on other sites More sharing options...
Geonovast Posted July 13, 2010 Share Posted July 13, 2010 Short in the ignition switch? Link to comment Share on other sites More sharing options...
Northup Posted July 13, 2010 Author Share Posted July 13, 2010 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. Link to comment Share on other sites More sharing options...
Geonovast Posted July 13, 2010 Share Posted July 13, 2010 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: Link to comment Share on other sites More sharing options...
Northup Posted July 13, 2010 Author Share Posted July 13, 2010 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? Link to comment Share on other sites More sharing options...
Geonovast Posted July 13, 2010 Share Posted July 13, 2010 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. Link to comment Share on other sites More sharing options...
Northup Posted July 15, 2010 Author Share Posted July 15, 2010 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. Link to comment Share on other sites More sharing options...
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