Rough idling and misfires in a late model Cherokee

[offctr]

I have a 2001 Cherokee with 31,000 miles on it that just recently started having a rough idle or miss at cold start and the check engine light came on. I took it down to the local Chrysler/Jeep dealer (Monroeville Dodge) as it is still under warranty and the service writer called this am telling me that there were two problems the first I understand and that was that the intake manifold debris shield (installed during a recall last year) had inadvertantly been positioned too close to a plug and caused "a single cylinder misfire" ---okay warranty item -easy fix no problem. Now then the guy tells me that there is also a "multiple cylinder misfire" caused by --get this "carbon buildup in the cylinder" requiring a $60 "combustion chamber cleaning" (already this sounds like hokum to me) some sort of chemical cleaning process which magicly removes carbon from interior engine surfaces. Also how you diagnose a single cylinder misfire underneath a multiple cylinder missfire is beyond me.
I think its in need of a tune up --but not at thier prices ($311.00 which also includes tire rotation --woo hoo !)
Like I said this whole carbon buildup thing sounds like BS to me as a way of charging me a whole lot more for changing some dirty plugs, and turning and unprofitable warranty repair/service into a profitable maintenence job. Anybody else heard of this process and whats involved --I already turned em down and told them to fix the miss caused by the debris shield only and reset the light..........
And how hard are plugs /wires etc to do on a late model Cherokee anyway ? I take care of the Wrangler myself but have left the Cherokee alone till the warranty runs out but the dealership service hard sell routine is getting old.
Unfortuntly the local dedicated Jeep dealership closed and Monroeville (PA) dodge took over the franchise, anybody know of anyplace better here locally?

edited by: offctr, Mar 06, 2003 - 05:09 PM[addsig]

[Bullet3600]

Sounds like their trying to make about $58 profit off you by putting in a $2 can of fuel injector cleaner which cleans the whole fuel system and removes carbon deposits. Sorry I can't help you with the wire change My Cherokee is much older but the engine misfire definatly sounds like a bad plug wire..........Bullet[addsig]

[dingus]

yeah, my first place to check would be all the spark plugs. how recently have they been replaced? how bout the wires? distributor cap and rotor? give it all these if it hasn't had them done already, i'd go ahead and do that. if that doesn't help out, then its your fuel injector(s)... pretty much any engine problem can be traced to either spark or fuel. spark is the easiest to diagnose (to me, anyway)...

i would take it to the dealer and have them fix whatever you can get them to do under warrenty, but don't pay for anything. you (with our help) can fix this for cheap.[addsig]

[offctr]

Actually the last time I looked under the hood I did not see any plug wires or even a readilly apparent plug location (possibly covered or shrouded) distributor etc I am pretty familier with the 4.2 and the older 4.0 as well as the 2.5ltr engines. Is the late model 4.0 (3rd gen?) distributorless ? Is this the OBD II that they ( the dealer) keeps telling me is so sensitive to carbon in the chamber, I know its BS but they have fallen back to: it's due to the OBD II or OBD 2 as the reason they HAVE to do this carbon removal --at my cost of course. I have refused becuase there is NO reason in my mind that carbon buildup in the combustion chamber will cause the engine to run rough or a cylinder to misfire unless the plug becomes fouled --at that point the plug needs to be cleaned or better off replaced. Cleaning the cylinder in my estimation is meaningless except during a rebuild as carbon buildup might affect readings of critical surfaces.
AND I feel that anthing that will remove carbon buildup from valve stems etc has got to have a pretty good chance of damaging seals and leaking down past rings into the pan etc. I have had experience with GM fuel injection cleaner that got through chemical resistant gloves and took skin off of my hand it was so caustic. So I am not too keen to put anything similar in my engine. Furthermore (as if this wasnt long enough) If the engine has that much carbon buildup at 31000. 1 where is it comming from ? and 2 wouldnt that much carbon indicate another problem and jarring chunks of carbon loose cause problems downstream?
The spark plugs are factory original and are due to be replaced as well as wires and such at this point. [addsig]

[Jeepr89]

There is a process that is used to clean carbon build up, I work at a service station and we have a deal I'm not sure how it works as all I do is pump gas and fix tires, but the process does work. I would try replacing the plugs, wires, cap, and rotor and see if the miss goes away. The reason they saw two codes is because if one code goes off it doesn't go off until the computer is reset so another code could have gone off before you got the cherokee into the dealer. If you don't think the dealership is treating you right call up Chrysler and complain. [addsig]

[jeepmaster]

tell them to go fist themselves, you can get ZMAX for 40 bucks and save that extra 20, and zmax cleans it all, its approved by the FAA and endorsed by motortrend. its the real deal, my friends Trans Am had BAD carbon buildup, it would blow out clouds of carbon when it hit second gear, and it stained his rear bumper around the exhaust outlets (white car, looked really bad) and his tranny was shiftin a little rough. he got ZMAX and the clouds and black exhaust stains are gone, the tranny shifts smoother now. just a thought tho, it imporves gas mileage as well. just my 2 cents
[addsig]

[mujaman]

zmax is definitely good stuff... a complete fuel and engine treatment. oh and by the way... it gives you a guaranteed warranty up to 150,000 miles on all the parts it covers as long as you use it every 6 months and send a little card in. everybody should get some![addsig]