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Old 07-30-2013, 05:39 PM
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Starting help!

90 YJ with 4.2L won't start!


This is driving me crazy. Starter works and turn over fine. Battery is charged. Replaced the ignition coil, distributor cap and rotor, plugs and wires.

It will crank until no end, but will not fire up. I have fuel.

The only time it fires up is when it is cold. But if I drive it for a minute and then shut it off it won't start again.
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Old 07-30-2013, 05:48 PM   #2
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sounds like carb

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Old 07-30-2013, 06:51 PM
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No. It has TBI.
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Old 07-30-2013, 06:57 PM   #4
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CPS??? You check for spark while warm???
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Old 07-30-2013, 07:00 PM
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Yes. Runs fine while it can. Maybe crank sensor?
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Old 07-30-2013, 07:01 PM
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If it was the cps, would it still fire every once in a while and continue to run?
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Old 07-30-2013, 07:11 PM   #7
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I would pull it and clean it for the hell of it. Can't hurt.
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Old 07-30-2013, 08:17 PM   #8
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Possible temperature sensor issue?????
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"For Gawd's sake, put a RELAY in there or you could burn the whole damn Jeep to the ground" ...this quote brought to you by people who do not understand the law.....Kirchoff's, Ohm's, or Faraday's.
Violation of KISS shall always ring false in TRUE engineering. - ME___
Had 75CJ5, 89YJ, 93YJ. Have 82CJ7 & 95YJ____Not one burnt yet due to lack of relays.
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Old 07-30-2013, 09:18 PM
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So the 4.2 was originally carbureted and didn't come with a CPS, but this jeep had a TBI conversion from the previous owner. Would a CPS have been installed at that time?

Here are some pictures of a sensor on the housing that could be that sensor.
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Old 07-30-2013, 09:20 PM   #10
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Check the fuel pump. Could be having trouble pulling fuel from the tank. I had the same problem and that's what fixed it
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Old 07-30-2013, 09:27 PM
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No. You can smell gas when it's trying to start. And when it does fire up and run it runs fine.
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Old 07-30-2013, 10:00 PM
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If it was the CPS, would that be an intermittent problem?
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Old 07-31-2013, 11:14 AM
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I'm going with the ignition control module first
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Old 07-31-2013, 10:40 PM
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Success! It was the ignition control module. Driving great now.
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Old 08-01-2013, 08:10 AM
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So replaced the ignition control module and it started fine several time last night. Drove it this morning for about 15 minutes and parked for about 5 minutes and it wouldn't start again. Seems like it only happens when it's hot. Any help or ideas in this
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Old 08-01-2013, 08:28 AM   #16
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First verify you have spark. if you have good spark make sure your fuel system is running properly, I.E. when you depress the Schrader valve on the fuel rail you get a nice spray of fuel. Also consider if no spark: bad ignition module - I know you just replaced it but could be bad or the processor may be back feeding to the IM. Bad processor - a portion of the CPU may have burned out. You may have a bad wire or bad ground, when you changed the IM you may have moved a wire or ground enough to make a good connection. The ignition switch may not be sending current to the ignition system or, again, bad wire.
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Old 08-01-2013, 09:41 AM
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I'm guessing at this point it is a bad wire. Will be doing a little fishing soon 👎
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Old 08-01-2013, 10:52 AM   #18
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another cheap thing to replace is the pickup coil if its not the fuel
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Old 08-01-2013, 12:00 PM   #19
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Correct me if I am wrong, but your Jeep still has the older style module, sits on the fender, Motorcraft Duraspark style. These had ground issues that would cause them to short out. Also, Motorcraft stopped making them, so all that is left is import stuff. Many old CJ ers are finding that the failure rate of out of the box modules is very very high. Could be you did find your problem, and then the new module burned up again. The napa around me can still test them.
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Old 08-01-2013, 06:15 PM
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It is in the fender. But I believe my problems are twofold. One is a bad wire somewhere (will be going through all wiring this weekend). Second is the throttle body gasket was bad and letting air in leaving a very lean mixture. I am able to start it every time with about a quarter throttle. The wiring is the other issue to fix to eliminate the previous owners mess.

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