'89 dieseling - JeepForum.com
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post #1 of 10 Old 06-24-2002, 06:02 PM Thread Starter
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'89 dieseling

Good evening all. I've just purchased an '89 YJ. Just recently it is 'dieseling' after the key is turned off. How do you set the idle / timing on the jeep? There seems to be no idle adjustment screws on the carb, just an electric motor that adjusts the throttle. The distributor cannot be rotated for timing. Is this the task of the Computer? The idle is around 900-1000 rpm. Any suggestions for the 'dieseling' ?

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post #2 of 10 Old 06-24-2002, 11:30 PM
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Could you maybe describe dieseling for me/us? Never heard that term before.

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post #3 of 10 Old 06-25-2002, 05:51 PM Thread Starter
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Sorry for the confusion...Diesling has been described to me as having the engine still running after the engine has been shutoff. I understand that there is sufficient fuel left in the engine and if the conditions are right, the engines continues to combust the fuel.
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post #4 of 10 Old 06-25-2002, 05:55 PM
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2.5 or 4.2?

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post #5 of 10 Old 06-25-2002, 06:07 PM Thread Starter
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2.5L 4cyl
manual steering
no air
Seems to be original carb w/TBI
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post #6 of 10 Old 06-25-2002, 06:38 PM
Jeff Merkel
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From what I've heard before, you're correct, it's a timing issue.

The timing is adjusted by rotating the distributor, though the screw to loosen it isn't exactly obvious. Looking at the distributor from the side of the car, the screw is sort of up and underneath to the right. If I remember correctly, a stubby wrench makes the job easier as their isn't much room to get in there.

I'm actually having dieseling problems myself. I have a Weber carb on, though, so I think the measured timing with a light is incorrect. Guess it's trial and error for me.

Good luck!

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post #7 of 10 Old 06-25-2002, 06:45 PM Thread Starter
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Jeff, thanx for the reply.........it's strange, the distributor housing is not typical from what i've seen. The vertical outside housing has an extension (that's the best i can describe it) that protudes horizontally from the shaft and is locked in place by this 'key' that fits under the distributor hold down bracket and bolt making it impossible to rotate the distributor.
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post #8 of 10 Old 06-25-2002, 08:44 PM
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Just my $.02...

I have a '90 YJ 4 cylinder and I had the same problems that you have. I have through my dimestore analysis come to the conclusion that it has somewhat to do with the electric Idle speed motor. What you can do to turn that idle down is adjust the bolt that sticks out of the end of it. I actually replaced mine, but I was idling that high too and it was real bad with dieseling at shutoff. I now have the idle around 750 and I don't have that problem. According to the Chilton's manual I have it should be at 670 + or - 80...I figure I'm on the high end.

So all in all you can turn the screw clockwise to force it in to the little plunger that pokes out. Careful not to go to far because you will force the plunger out of the holder thus breaking it...I speak from experience. It is a metric bolt, can't remember the thread, but if you have to you can even pull the bolt out and replace it with a shorter one from the hardware store. I did that and the dieseling problems are almost gone. The only time I get dieseling is when I kill the engine when I don't let it settle down to idle speed.

1 last thing, get some o2 sensor safe carb cleaner and hose out the carb good while running and that will help the situation to make sure that the Throttle Position Sensor isn't gummed up.

Hope this info helps and let me know if you need pictures etc. BTW new speed motor is $60 at NAPA if you break it..real easy to swap.
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post #9 of 10 Old 06-25-2002, 08:53 PM
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Devo45, I think you're right because I believe the ECU controls the timing and the old "turn the distributor" adjustment procedure is for the 4.2 only. Furthermore, the ECU controls mixture also, so you're out of luck there too (sorry!). I guess carbon build-up could be a factor considering the age and if it wasn't maintained real well, but I don't know what else to suggest.

Not to walk on the thread, but Jeff--you should be able to still adjust timing as usual even with the Weber, I did it just this afternoon to try and squeeze a little more advance. As long as the vacuum advance hose is disconnected and plugged, and the light is attached to the #1 plug wire, you should be good to go. Make sure that the vacuum for the vacuum advance is coming from the stock location (that gold-tone thing that protrudes from the intake manifold near the EGR) and not the side of the carb--the carb outlet is ported vacuum for pre-1983 (I believe, whenever they changed the distributors).

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post #10 of 10 Old 06-25-2002, 09:01 PM Thread Starter
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thanx all, I've tried the small bolt on the throttle motor, but a shorter length is a good idea. I'll keep pluggin away at it. There is a high pitch sound coming from the front of the transmission hump that goes away when I give it some throttle. Vac. leak maybe? I've tried the carb cleaner and even a stethoscope to pinpoint the noise, but no luck yet.
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