Slight misfore at idle

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SilverXJ
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Slight misfore at idle

Post by SilverXJ »

So, I have a slight misfire at idle. I can feel it and hear it in the exhaust. The computer doesn't complain about it and it isn't that bad. It has been there in this stroker and all previous versions. I would like to know if there is anything I can do about it? While it isn't bad I would still like to have everything 100%.
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Re: Slight misfore at idle

Post by Exos »

Isn't this simply due to the idle characteristics of the Comp cam?
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Re: Slight misfore at idle

Post by SilverXJ »

Could be.. but does a slightly lumpy idle mean a slight mis?

I wonder if anyone else with a CC 68-231-4 can verify that they too have a slight mis at idle
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Re: Slight misfore at idle

Post by dwg86 »

SilverXJ wrote:So, I have a slight misfire at idle. I can feel it and hear it in the exhaust. The computer doesn't complain about it and it isn't that bad. It has been there in this stroker and all previous versions. I would like to know if there is anything I can do about it? While it isn't bad I would still like to have everything 100%.

I wouldn't think the comp 68-231-4 would have a lumpy idle. If its been there before, check parts that were used on all the engines. Like maybe coil rail, fuel injector harness. All this computer controlled fuel injection stuff is new to me(I am learning). Maybe take it to a Dodge dealer and have them set your cam and crank sensor with thier scanner equipment. Since the cam is set up different than the stock cam(advance and valve timing events), maybe that could be the problem :huh:

Silver, you are the guine pig for my build. I am reading and taking notes.
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Re: Slight misfore at idle

Post by John »

What is your idle speed? Is it a little high? I have that cam in a yj. no misfire and not lumpy by my standards.
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Re: Slight misfore at idle

Post by SilverXJ »

I wouldn't call it a lumpy idle by any standards. It is smoother than my Zj with 190,000 on it. Its slightly rough (which comp cam says it will be), but not enough to make things inside vibrate. I am happy with the idle quality, but want it to run as smooth as possible. If it is from the cam then fine. There is just a slight mis at idle, which is mainly noticeable in the exhaust note. Idle is around 750 RPM. I don't think it would be the injectors or coil rail because it runs find other wise. Off idle and the mis isn't there. Cam sensor position is a good point. Perhaps I'll visit the local Jeep dealer... crap.. I would have to do it before June 9th when they close.
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Re: Slight misfore at idle

Post by rile86 »

I have been having the same trouble with my 4.6 i just installed in my 00 wrangler. Its also noticeable at 1800 rpms. Runs great while driving though. Havent been able to solve the problem. Where you ever able to find the problem.
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Re: Slight misfore at idle

Post by superstingray77 »

Silver, i had that cam in my last version of stroker and there were no misses in the exhaust and it idled as smooth as stock.
I wonder if your running stock valvetrain (rockers non adjustable etc) is perhaps the rocker/lifter pre-load too high causing one valve perhaps not to seat all the way? This could become only evident when the engine is warm not cold and will cause a lisp in the exhaust. Eventually it will burn that valve if not corrected, but wonder if doing a warm compression test and identifying the offending cylinder which would yield the lowest cranking pressure. Fuel and ignition are good or you would have a high rpm miss.
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Re: Slight misfore at idle

Post by SilverXJ »

superstingray77 wrote:I wonder if your running stock valvetrain (rockers non adjustable etc) is perhaps the rocker/lifter pre-load too high causing one valve perhaps not to seat all the way?
I have adjustable rockers and even if I had stock valve train it would not be setup with too much preload, that is just sloppy.

The cam definitely didn't play well with the PCM. Chris@christuned tuned most of the idle and start issues out. Swapping the cam out fixed it all though.
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Re: Slight misfore at idle

Post by 6TIME »

Silver, Is the misfire steady or does it seem to cycle in some sort of a pattern? Also is the O2 sensor operating normally with the ECU in closed loop? If your idle vac is above 15-16in the computer should not be bothered much. The 231 cam is considered very mild for a motor of that displacement (46-47ci/cyl) and should not be causing any sort of misfire at idle unless there is vacuum issues.
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Re: Slight misfore at idle

Post by SilverXJ »

There was no real pattern to it. It wasn't the CC 231, but the Hesco RVOB. O2 sensors working fine. I think idle vac was 16-17, compression was 155 across the board
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Re: Slight misfore at idle

Post by 6TIME »

Are you running the O2 sensor in closed loop? I've seen many stock 4.0's with 16-17 idle vac. I highly doubt the cam is causing your misfire. The ECU on my 93' really likes to cycle lean/rich when in closed loop mode. I swings lean enough that it puffs a few times every time it cycles from the lean side at idle. And that's with stock 4.0, 4.0 with 232-4 cam and 24lb injectors, and the 4.6 with lunati cam....They all have behaved the same. Idunno if your ECU operates in the same fashion since yours is newer? I chased the misfire for a while until I installed a AF gauge and realized that it was how the thing is designed to work. In open loop it idles perfect....
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Re: Slight misfore at idle

Post by SilverXJ »

Yes, it is in closed loop. No, it stays right around 14.7:1 or so.

Anyhow, it has been solved as the cam has been replaced and all symptoms are gone.
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Re: Slight misfore at idle

Post by superstingray77 »

Hey Silver, I figured as much on the lifter preload :-) hopefully no offense there. Hell if anything that head should grow .008 as she heats up.. seems to be about what I see on my cold/hot lash on the solid cam. Does not make sense that it would be the cam, mines a monster and I have no lisps/misses even ice cold idling lean at 17.0:1 (sounds mean as hell though. rofl..
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Re: Slight misfore at idle

Post by 6TIME »

What cam did you swap in?
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