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Diagnosis - Ignition Switch Problem


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Can someone help diagnose this problem?

 

1988 Comanche 4.0L (5sp) - When the key in the ignition is held all the way forward (crank Position) the engine will fire and run. When the key is released back into the run position ... the engine dies. If the key is held forward in the crank position it will stay running even after cranking.

 

This is not my Comanche, but this is how the problem was described to my over the telephone. I have been reading the Chilton manual for possible diagnosis, but it is difficult to narrow it down without putting a voltmeter on the parts. What would you guys suggest I look at first?

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This is the exact question that helped me find the comancheclub. For me, it was a wire (fusible link) connected to the starter motor relay. Its located near the battery abd has a lot of wires going to a pin/screw. I can check which color wire it was if you want. I ended up having a shop do it because I couldnt track it down. I'm pretty sure its the one with the nice shiney connector on it ;) LMK and ill check the color of the wire

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Actually, I don't think it is a fusible link. Just the red wire coming off the post/screw on the starter relay; it runs into a wire loom then toward the battery. If the wire looks good I would try putting a new ring terminal on it and cleaning up the connections. Post back and let us know if it works.

 

I was reading jeepforum today too, where someone had a similar problem and he said it ended up being something unplugged up near the firewall near where the wiper motor is. I don't know what that could be tho :dunno:

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Compared to most modern vehicles, the comanche's wiring is pretty simple, I did this today actually. Uncork the big mess behind the battery, then pop all the wires out of their protective black sheaths, take a flashlight and follow every wire too and from the starter then to the box on the firewall near the steering wheel. You should find your problem, any rusty connection will usually make a comanche crap out.

 

Could also be a $#!&ty ignition lock cylinder in the column, click the key forward one click and wait for fuel pump noise, if you hear it then I guess you can rule out cylinder.

 

Take mine for example I can start my truck without a key. And it runs great. Just turn the cylinder.

 

P.s. Before anybody gets on me, there is a hidden kill switch.

 

Ryan,

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What the original post describes is what happens when the ballast resistor for the fuel pump goes bad. The ballast resistor is that grey/white ceramic thingie on the inside of the driver's front fender, next to the air box. Normally, power to the fuel pump goes through this resistor, which drops the voltage to around 9 volts (IIRC) to reduce noise and make the pump last longer. During starting, the ballast resistor is bypassed so the fuel pump gets the full 12 volts. So when the key is in the START position, there's 12 volts going to the fuel pump through the bypass circuit. When the key is released to the RUN psition, the bypass circuit goes away and power goes through the ballast resistor. If it's broken -- the fuel pump stops when you release the key, and the engine dies.

 

Simple test -- find the ballast resister, and jumper across the two terminals. If the engine keeps running -- there's your problem.

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When mine was doing this I tried jumping the ballast resistor and replacing it, It didnt help. I also changed the ignition switch and it also didnt help.

 

eagle, do you know what connector near the firewall the guy on JF could have been talking about.

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eagle, do you know what connector near the firewall the guy on JF could have been talking about.

Yeah, he's probably talking about the C101 connector. It's the big box that the main harness runs into and out of, high on the firewall directly in front of the driver. There was a factory TSB about cutting it out and splicing all the wires together, and by mid-1989 the factory had eliminated the C101 connector.

 

I don't think that's likely to be the problem in this case. If it were the C101. the engine wouldn't start at all. My money is on the ballast resistor.

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I appreciate all of the advice. I hope the problem is just a ballast resistor. I bought one for $9 just in case. I can always take it back. I have noted all of the other problems too just in case.

 

I am going to see if I can get the Comanche going tomorrow morning.

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I appreciate all of the advice. I hope the problem is just a ballast resistor. I bought one for $9 just in case. I can always take it back. I have noted all of the other problems too just in case.

 

I am going to see if I can get the Comanche going tomorrow morning.

You could have just jumpered it .. as I suggested. The 87s didn't even have it -- the ballast resistor was added in 1988 to reduce the amount of noise generated by the fuel pump.

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It is possible to move the ignition switch mounting screws a bit...so if the switch is loose, it might go forward enough to start it, but not enough to keep it running....make sense? It's at the bttom of the column, on the top side.

 

But the ballast resistor is also a certain idea. Jump it first before installing a new one, as electrical parts usually don't get returned. But then again, for $9 it's a good cheap spare.

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after thinking about this for a while it is also possible the screw inside the ign column could be loose. when i removed mine there were two or three places in the column by the ign sw that were worn. my ign sw had unnatural movement when i turned the key. mine is a 88 so yours being an 87... maybe.

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