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Unread 10-14-2011, 09:15 AM   #1
bluedaffy
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1989 YJ Wrangler 
 
Join Date: Oct 2011
Location: Stevens Point, Wisconsin
Posts: 286
dieseling

Can a high idle be the main source of dieseling? When I kill my wrangler when idling at around 1000-1200 rpms it will often diesel. When I kill it around 700-800 rpms it very rarely will, and even in those situations it is usually just a hiccup. I would like some feedback because I feel like a well tuned machine wont diesel regardless of idle speed. Is this the case?

My wrangler is a 4.2L. with the Carter.

By the way, the reason it idles at different speeds is because I just reset the idle speed. The previous owner had it set high to over come what I'm guessing was a gummy carb (because thats the condition it was in when I got it). I have since cleaned the idle tubes and carb and it idles very steady at whatever rpm its idling at. but I dont know if its loose springs on the throttle arm that keep the idle screw from being tight against the idle post or if the throttle needs to be lubricated cause when I let off the gas sometimes the idle screw returns all the way back to the idle post and idles at ~700 rpms and sometimes it stops short and idles ~1200 rpms.

Thanks, bluedaffy

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Unread 10-14-2011, 10:06 AM   #2
LordEnki
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Incorrect timing may be the cause. It may need to be retarded a bit. Sorry, but this is the extent of my knowledge on the subject. Good luck.
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Unread 11-23-2011, 09:41 PM   #3
bluedaffy
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Thanks but I just got done trying to retard the timing to remedy the dieseling... still there. I really thought that might have been the solution.

I read somewhere else that the alternator may be causing some sort of feed back in the wiring that can cause this. I will look into it more but anybody else out there that might have a probable cause for me would be much appreciated!
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Unread 11-23-2011, 10:41 PM   #4
89yjsahara258
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1989 YJ Wrangler 
 
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Location: Victoria, BC
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You would need to Advance the timing if timing is the culprit. Is your computer still in the loop? A very rich situation can also cause it to diesel. Prior to swapping in an MC2100 my post nutter Carter's stepper needles were not in the suggested position and until I fixed them it ran very rich and dieseled all the time.

The other side of this is that I had a dieseling problem after installing the Motorcraft and it was due to the timing being too retarded therefore advancing the timing solved the problem.

Good luck,

Spencer
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Unread 11-23-2011, 10:51 PM   #5
WindsorRenegade
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1991 YJ Wrangler 
 
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I agree with running rich. You could be burning excess gas left in the chamber, especially if your engine is running hot.
That's about all I know as well, good luck!
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Unread 11-24-2011, 07:29 AM   #6
Karma
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HI,
From what I have read, dieseling is caused by carbon build up in the combustion chambers. When the engine is running the carbon glows red hot. Then when the ignition is turned off (now no spark) the carbon continues to glow and ignites the mixture still coming from the carb.

I don't know if dieseling happens with fuel injection because when the ignition is turned off, there is no power to the injectors thus no gas can get into the chambers.

Personally, I have never had the problem so I can't give first hand experience.

Sparky
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Unread 11-24-2011, 07:38 AM   #7
bluedaffy
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My computer is still in the loop, tried to nutter it last night with but couldn't figure it out with aftermarket Jacobs electronics unit. She is running rich, I've looked down at the needles and they appear to always be buried in the carb. I have the mixture screws in the bottom front of the carb almost completely out and it isn't changing the needles at all, it does make the overall sound of the idle smoother however.
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Unread 11-24-2011, 08:15 AM   #8
pasinbuy
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Is you Yj suppose to idle at 1000 to 1200. That sounds a little high to me and could just be your problem. I would guess that 800 to 900 rpm would be right.

And to answer your question. Yes, high idle can be the cause of dieseling.
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Unread 11-24-2011, 09:12 AM   #9
bluedaffy
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no you're right it should be dieseling around the 800 range but for whatever reason I can't seem to dial it down that far. Furthermore I can't figure out why it is ALWAYS RUNNING RICH, I've tried adjusting the mixture screws with no luck.... I need to upgrade to a better carb but in the mean time I'm losing weeks of my life trying to fix this beast.
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Unread 11-24-2011, 09:39 AM   #10
Karma
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HI All,
I think many of you are missing the point. After you turn off the ignition, THERE IS NO SPARK. THEREFORE THE PROBLEM CANNOT HAVE ANYTHING TO DO WITH IGNITION TIMING. There is no spark to light things off.

Sparky
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Unread 11-24-2011, 10:49 AM   #11
89yjsahara258
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Having the engine timing retarded too far requires more fuel in the cylinder via a further open throttle plate. This extra fuel in the cylinder can cause the dieseling or detonation. To prove this, when you advance your timing the engine speeds up requiring you to lower the curb idle speed. The reverse is also true, when you retard the timing the engine speed slows requiring your to open the throttle plates further thereby putting more fuel in the cylinders.

From my own experience I mistakenly set the 8* BTDC on my jeep after the nutter while holding 1600 rpm. This put my initial timing well retarded. The vehicle would still run but had considerably run on after I shut if off.
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Unread 11-24-2011, 11:13 AM   #12
dancytron
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1990 YJ Wrangler 
 
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I know on mine the carb needles were just stuck. When I did the Nutter, I had to take them out and spray them with something (I don't remember what I used, whatever I had around either PB Blaster or something else) and work them loose for about 15 minutes to get them where I could move them to the middle. If yours are stuck all the way in, that's why it would be running rich and the computer must be going crazy like mine was.

I'd take the needles out and try to free them up and go from there. Don't drop the little screws that hold it on, I spent two hours searching for the one I dropped before I found it. Then you can decide if you want to do the Nutter or not.
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Unread 11-24-2011, 12:18 PM   #13
Karma
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HI All,
I am only talking about the dieseling problem. Nothing else.

Sparky
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Unread 11-24-2011, 01:47 PM   #14
89yjsahara258
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Quote:
Originally Posted by Karma View Post
HI All,
I am only talking about the dieseling problem. Nothing else.

Sparky
Go and retard your timing, let it idle for a few minutes and then shut it off. Depending on how far you retarded the timing the motor will either diesel or shut down roughly.

If the ignition is not advanced enough while the vehicle is running it can not burn through all the fuel which combined with the hot engine causes the dieseling.

Spencer
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Unread 11-24-2011, 03:40 PM   #15
pasinbuy
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Quote:
Originally Posted by bluedaffy View Post
no you're right it should be dieseling around the 800 range but for whatever reason I can't seem to dial it down that far. Furthermore I can't figure out why it is ALWAYS RUNNING RICH, I've tried adjusting the mixture screws with no luck.... I need to upgrade to a better carb but in the mean time I'm losing weeks of my life trying to fix this beast.
The idle mixture screws do not adjust weather you are running rich or not. They control idle. and slow smooth idle running. Your jets control running rich or not at regular speeds. Have you pulled a plug to see if you are really running rich?

It has been a while since I set up a carb although first set your idle rpm. This is the screw at the end of the cable on the outside of the carb. Then turn the idle needle screw to set the idle mix to smooth out the motor.

The idle rpm screw adjustment is out side of the carb attached to the carb butter fly rod.

I would try about 800 rpm and see if the dieseling stops, if not go a little lower in rpm until the dieseling stops. 1200 rpm is way too much.
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diesel , idle , idle problems , idle speed , shutting off

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