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Unread 04-08-2012, 06:37 PM   #1
MarcF1977
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Join Date: Mar 2012
Location: Minneapolis, Minnesota
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No Spark and out of ideas, please help!

Hello, I'm a novice to auto repair and I've tried everything I can think of to get my CJ7 started, and am out of ideas. Its an 86 CJ7, 4.2L. I've replaced the solenoid, starter, ignition module, ignition coil, plugs/wires, distributor, distributor cap/rotor, and the battery. Its turning over, but I'm not getting any spark. Not sure what else I can try replacing. Any of your thoughts or ideas would be greatly appreciated!

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Unread 04-08-2012, 06:39 PM   #2
clydegoat
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Have you check to see if your coil is getting power? maybe either way there will help you know if it's before or after that. maybe help
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Unread 04-08-2012, 06:41 PM   #3
LT1CJ7
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1983 CJ7 
 
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Check the ecm fuse.
I bought a super clean all original CJ7 for dirt cheap because it didn't run.
The owner took it to three shops which they could not find the problem.
They also replaced every part like you did.
A 20 cent fuse and I was cruising.
I think it was a 3amp fuse labeled lights or cluster.
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Unread 04-08-2012, 06:56 PM   #4
pman
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I once had a similar issue on my Wagoneer...ended up being the ignition switch located midway down the steering column under the dash. It would crank, but I wasn't getting fire.
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Unread 04-08-2012, 09:46 PM   #5
BagusJeep
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1981 CJ7 
 
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Thought No. 1 - DO NOT REPLACE ANYTHING ELSE.

You are doing what a lot of us do, replacing bits without finding the problem. In a 25 year old CJ this is at best replacing bits before they fail, at worst introducing further issues. Find the problem first.

Thought No. 2 - BUY SOME TEST GEAR

Simple stuff on a CJ. A 12V test light, not LED, which you can make out of old junk or buy for $5, will allow you to test the low voltage side. A multimeter is useful but not AS USEFUL.

Thought No. 3 - TEST IT
If you dig up Jeephammer's old posts you will find a number of simple test procedures that will pinpint which part of your system is not working. Be methodical and you will find the root cause.


__________________________________________________ ______________________________________

Having said all that, here is what I would do. I followed JH's test routines and discovered a short at the ICM plug. Yours will no doubt be different.

If you want a simple test hook that lamp up between the red with tracer wire at the coil (disconnect it first) and the -ve terminal on the battery. A dim bulb in Run, a bright one in Start. That confirms you have coil voltage. If you do not then you have a wiring problem smewhere, see below diagram.

Hook the lamp between the +ve battery terminal and the green wire from the coil. When you try and start it should blink, that confirms you have a ground signal from the ICU in time with the engine. If you do then the pckup in the distributor, ICU and computer are working.

If those check out it is the coil or the distributor.

Put the wires back on the coil. Take the lead from the centre of the distributor, connect it to an old spark plug and rest it on the cylinder head. In Start you should get a healthy blue spark and snap.

If so then look at the distributor. Take any lead you like and repeat the spark plug test.

By this time you should have isolated the problem to one specific area. Report back and we can look closer at that area.

It should take less than 5 minutes to do that testing.

If your ignition is standard here is a simple diagram of the wiring that may be of help. Yours is slightly different as it has a feedback loop from the ICM to a computer that is itself wired to the fusebox. The fuse referred to above is the IGN LPS fuse, worth checking as that pesky computer will stop the rest of it from working IF you do not have a signal on that green wire.
schematic-ignition-layout.png  
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