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Old 02-19-2011, 03:44 PM   #1
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93 YJ 6Cyl 4.0 Starting Issue

I have a 93 YJ 6Cyl that is having a starting issue. It turns over fine and has fuel pressure in the fuel rail, but it is throwing no spark from the ignition coil to the central distributor post.

i have checked all of the fuses and the attachment of the Crankshaft Position Sensor. do i try replacing the ignition coil? the CPS? is there another sensor that would prevent the spark?

thanks.

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Old 02-19-2011, 07:46 PM   #2
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Start with the coil it's an easy fix.

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Old 02-20-2011, 09:10 AM   #3
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I would check for voltage at the coil before i replaced it. If you have no voltage with the key on, its NOT the coil, its your Computer.....
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Old 02-20-2011, 12:00 PM   #4
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try unpluging the plug to the pick up coil . if its green inside it s not making good contact. cheep and easy change. probably needs change any way.
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Old 02-20-2011, 12:15 PM   #5
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great ideas! thanks.

i will try all of your suggestions today in order of increasing cost and complication. i will also post an update soon. thanks for the help.
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Old 02-20-2011, 09:07 PM   #6
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Update! no luck.

i cleaned and tested the voltage on the ignition coil first, and was getting a low background charge. Based on this, I replaced the ignition coil and no luck. i retested the spark and was getting a spark between the ignition coil and the coil wire, but not between the coil wire and the center distributor post. this lead me to wires, so i replaced them and the plugs (why not?). so far, no good. what else am i missing; the Crankshaft Position Sensor?
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Old 02-20-2011, 09:12 PM   #7
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Check the cap and rotor, sometimes the button burns up or the tab that contacts it on the rotor is damaged.
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Old 02-20-2011, 09:44 PM   #8
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yeah. the cap and rotor is all i have left to try. is there anything else even involved in the ignition system?
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Old 02-20-2011, 09:50 PM   #9
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while you have the cap off make sure the rotor is turning.
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Old 02-22-2011, 08:35 PM   #10
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Question Update: I learned that I didn't know much.

Ok, here is the update from my latest efforts.

I went to go get parts and got into a discussion with the parts guy which was inevitable. I told him what I had done so far. He pointed out the Crankshaft Position Sensor on the flywheel housing and the Camshaft Position Sensor in the distributor. He said that you should be able to detect the electrical pulse charge from both of these sensors when they make their detection.

I proceeded in this direction. I removed the distributor cap. The rotor was worn, but not overly corroded or broken. I verified that the rotor did turn when the starter moved the engine. The contacts on the inside of the distributor cap had some buildup but not too bad.

I attempted to test the Cam Position Sensor. I used a multimeter on the 20V setting and tested post combinations on the snap plug for the Cam PS. There are three posts in the plug and I tried all combinations while having the engine rotated. I got no signal from the MM. I then reconnected the cable and attempted to get a charge off of the actual magnet in the sensor in the distributor. I also got no signal.

I then moved on to the Crankshaft Position Sensor. I pulled the snap plug and tested all post combinations while having the engine rotated. I also got no signal.

I am not confident enough that I performed the tests correctly to buy either sensor to replace. Any ideas on the correct testing process? You can see more in the photos. Thanks.
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Old 02-23-2011, 06:58 PM   #11
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I'm in the same boat I've replace coil, pick up coil, cap and rotor, yj still not firing... Ive been bouncing all over the net to find answers, check all your fuses, something i've seen people say, also Ive also seen that you (supposedly) cant use a digital read out multimeter to do some of these test's, that you need a analog mutilmeter...
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Old 02-24-2011, 12:22 AM   #12
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I had the same problem with my 96 xj 4.0L checked every thing even replaced the computer with no luck finally ran in to an old friend who just happens to be a jeep mec, he said don't even waste your time with the computer they usually never fail, replace the cps and it will fire, and sure enought he was right.

Good luck
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Old 02-24-2011, 01:40 AM   #13
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Had the same problem with mine. Went as far as getting a known working computer and it did no good. Changed the CPS and vroooom I was in business.

The CPS is on the drivers side above the flywheel on the housing.
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Old 02-24-2011, 06:08 AM   #14
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I'm not sure about the cam sensor, but the crankshaft sensor pulses way too fast for a multimeter to pick up. You would need an oscilloscope to test it. Unless you already have/can borrow one it's much cheaper to just replace the sensor.
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Old 02-24-2011, 10:34 AM   #15
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Thanks for the information.

Thanks for the suggestions. It seems that the consensus is that I should replace the Crankshaft Position Sensor next. I'll do that right away and update the community. Thanks for everyone's help. This has been frustrating as you all know.

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