1990 YJ 4.2 Dies at Idle

[14JK-U]

my 1990 YJ has just started to die at Idle or low speeds (such as slowing down to turn into my driveway). on a cold start it works fine, if I drive it until it's warm the symptoms start acting up, when it dies its hard to start but if I hold the ignition it will eventually kick itself back to life before it sputters and coughs itself to death. ive found other threads on forums from a quick google search but they all end up the same way, throw parts at it until it works.

 

[wjtstudios]

They were still carborated in 1990 correct? First thing I’d go after is your fuel filter. Cheap part to replace. As the engine dies the lack of pressure can let the debris fall inside of the filter and open it up. Once it gets going again, it clogs back up under pressure. If that’s not it, I’d start looking into the carb.


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[14JK-U]

correct they were carb'd until '91 when they went to the 4.0, I replaced the filter for a whopping $5 already with no fix to the issues. currently trying to find a good replacement carb but it looks like the weber 32/36 is the best option for $300 shipped. i'm on the fence if it's the issue since the stock carter is still dropping fuel into the bowl at good pressure. guess i'll pull the trigger regardless since it's still an upgrade.

 

[QuicksilverJK]

The stock 4.2 carb is a real pain to work with. But before you throw parts at it check for vacuum leaks. If I remember right there is a mess of vacuum lines on that engine. Also make sure the base of the carb isn't leaking vacuum. If that all checks out either rebuild and tune your stock carb or look into a replacement. After carb and vacuum are done you will want to verify and set ignition timing.


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[14JK-U]

The stock 4.2 carb is a real pain to work with. But before you throw parts at it check for vacuum leaks. If I remember right there is a mess of vacuum lines on that engine. Also make sure the base of the carb isn't leaking vacuum. If that all checks out either rebuild and tune your stock carb or look into a replacement. After carb and vacuum are done you will want to verify and set ignition timing.


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yep, the vacuum lines and birdsnest of wiring in these things makes me want to bang my head against it. i'm honestly not even sure where to start testing most of the lines for vacuum leaks since over the last 28 years these lines have been capped/hidden/rotted/etc

 

[QuicksilverJK]

yep, the vacuum lines and birdsnest of wiring in these things makes me want to bang my head against it. i'm honestly not even sure where to start testing most of the lines for vacuum leaks since over the last 28 years these lines have been capped/hidden/rotted/etc

That is exactly how I remember my 1st jeep. Mine was an 88. If you can track down a vacuum diagram I would just buy a roll of vacuum hose and a box of various fittings and just rebuild the whole thing per the diagram. As many headaches as that old jeep was I wish to this day that I never sold it.


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[Graywolf]

Take a look at the throttle pin and take a hold of it at the throttle cable connection and try to move it up and down or side to side. If it moves at all you will need to have the pin knurled or replace the carb. It is letting to much air in and the ecm keeps trying to add more fuel. Therefore not running at idle when warm.