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Old 06-23-2013, 12:30 AM   #1
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Engine knocks when shutting down.

I have a 1987 yj with 4.2L. In last few days she has started intermittently shaking and knocking when I shut her off. I know there are probably many things that can cause this. What I am looking for is ideas to explore. I am not very knowledgable but I am learning. Thank you in advance.

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Old 06-23-2013, 01:25 AM   #2
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Sounds like diesling. Old motor could be carbon buildup. New it could be running lean.

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Old 06-23-2013, 01:47 AM   #3
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Sounds like diesling. Old motor could be carbon buildup. New it could be running lean.
Ok I will do a research dieseling. What do you do to treat or repair this.
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Old 06-23-2013, 08:50 AM   #4
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Tune up, check your timing and idle. Idle hot in park/neutral should be no more than 800 rpm's. Worse case scenario, extreme carbon build up or a bad distributor. I would make sure everything is set to spec. You might just need a tune up.
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Old 06-23-2013, 01:08 PM   #5
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Tune up, check your timing and idle. Idle hot in park/neutral should be no more than 800 rpm's. Worse case scenario, extreme carbon build up or a bad distributor. I would make sure everything is set to spec. You might just need a tune up.
Very interesting, because the RPM's recently have been going up to 1500 when I put her in park. I thought that was a little high, I did not realize she was supposed to be at 800. What are other symptoms of bad distributor?
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Old 06-23-2013, 10:24 PM   #6
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Very interesting, because the RPM's recently have been going up to 1500 when I put her in park. I thought that was a little high, I did not realize she was supposed to be at 800. What are other symptoms of bad distributor?
That's your problem. If you shut it down at 1500 rpm's hot it's going to diesel/run on. Bring your idle down. It actually should be 700-750 rpm's but they seem to like to idle at 800. That should be max. Your distributor is probably fine, start with the proper idle adjustment.
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Old 06-23-2013, 10:46 PM   #7
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That's your problem. If you shut it down at 1500 rpm's hot it's going to diesel/run on. Bring your idle down. It actually should be 700-750 rpm's but they seem to like to idle at 800. That should be max. Your distributor is probably fine, start with the proper idle adjustment.
Thank you, I will have to look up how to adjust idle. Is it a tricky process where I should take it to a professional or is it something you can just look up on Internet?
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Old 06-23-2013, 11:13 PM   #8
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It is just a screw, I have a weber and its on the back side of the carb, just look for where your throttle linkage is and there should be a screw to adjust the position

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