[Guest]

HI folks. I am new to the board, found this board when I was looking for info on my problem. Well here goes. My check engine light came on about a month ago on my'01 Cherokee Sport. The vehicle had been sitting at idle while I went in a store for approximately 30 minutes. When I came out the light was on and has not gone off since. So, yesterday I finally got it into the local dealership for a check. After 4 hours of waiting they told me the code the computer has stored is P0306, indicating a misfire in cylinder 6. The tech said that it is misfiring about once every 300 fires. Now, he told me that this is right near the acceptable range for misfires and I should not worry about it. He overrode the check engine light and reset it so that I didn't have to look at it, assuring me that it probably would not come back on again. Also, the tech said he switched the spark plugs in cyliders 6 and 3 and still saw the misfires in cylinder 6. SO, it's not the plugs. Anyway, needless to say the light came back on yesterday about 4 hours after I pulled out of the dealership. Again, the vehicle was sitting idling while I was talking to my accountant and when I got back in the light was on. So, does anyone have any idea what is causing this. My only thought is that it's the coil pack. The electrical stuff is out of warranty on my vehicle as it has hit 80,000 miles. So, I would like to avoid a costly trip back to the idiots at the dealership. ANybody have a solution or hints. Thanks a bunch. Sorry for the lengthy post.

 

[Guest]

You shold not let your vehicle idle for 30 mins. In fact, your owner's manual more likely than not states you shouldn't let it sit running for more than a minute or so... Also, your '01 has 6 coils, one for each plug. I would suspect the number 6 coil. Also, since it appears that you are in the habit of allowing the vehicle to idle for extended periods I would also inspect the EGR system. Take it to another dealership or repair shop and have them check it out.

 

[Guest]

As far as the idling goes, I live in an area where we spend 5 1/2 months at severe below 0 temps. They actually recomend that you leave the vehicle running in this weather as b/c it is easier than starting it in this cold. I don't have another dealership in my area. There is one that services all Dodge, Jeep, Chrysler etc. Can you buy just the number 6 coil and replace it? I don't know, but if you can I think I'll try that and see how it goes from there. Also, once the problem is found and repaired will the light go out on its own or does the dealer have to reset it? Thanks.

 

[2586]

Nobody knows were you live because your profile is not filled out.

 

[Guest]

Yup, you can buy just one. I imagine they are pricey and I would rec that you get someone else to look at it to make certain that it is the source of the miss. In most cases codes identify symptoms- they almost never reveal the source of the problem. Like in your case- the code reports a misfire. It doesn't report which cylinder or why.

 

[Guest]

I realize you live in a cold area, but 30 minutes is too long in my opinion. Its not like your starting after a cold night, just a few minutes wait and the battery should be just fine turning a recentely cold motor vs. a motor cold overnight. Just restart every couple hours.
Gasoline motors strip oil from the cylinder walls as they run if even a slight bit rich, and at idle most motors are very inefficient.
Anyway, have you checked the gaps on the plugs? I know he switched them to check, but a poorly gapped plug will exacerbate a weak electrical system.

 

[stump_breaker]

In 2000 they had a coil for every two plugs. Did they change in 2001? If they did I got robbed!

 

[Guest]

1-2....who's countin'? maybe I'm thinking kj. At least I didn't drive my xj into a pond......

shoulda put your flamesuit
on....

 

[NIX]

In reply to:

At least I didn't drive my xj into a pond......

[/ QUOTE ] Ouch, that 's gotta hurt....

 

[Guest]

In reply to:

Gasoline motors strip oil from the cylinder walls as they run if even a slight bit rich, and at idle most motors are very inefficient

[/ QUOTE ]

*WRONG* Even the state inspects ALL VEHICLE'S pollution levels at idle because it is at it's MOST efficiant levels. They KNOW the level is much higher while driving normal revs and at WOT (wide open throttle) The only time the engine should ever really need to run rich is starting up. Optimal mix is about 14 (+-1) parts per 100, fuel to air mix.

State troopers, Cab drivers, Pizza Delivery guys leave their motors running for HOURS, sometimes 8 hours at a time. If your mixture is correct, it's harmless and wear on the engine is much lower than a vehicle that has been started over and over at every stop. Provided your cooling systems are in good order and that you change your OIL at the recomended service levels (this might come under severe service by definition), you SHOULD be able to Idle that motor till it either overheats or you run out of gas. My '90 has a 6 quart oil pan and a 4 core radiator, that's MORE than enough to let it go for 30 lousy minutes, even in summer's heat.
If there is a spark plug wire between the pack and the plug, you might replace it and put some di-electric grease on it's ends, prior to install and replace the old spark plug with a new one. You might gap it a thousanth or so closer than normal. (just a hair, man.) After that, I'd be looking to see if there is a crack or build up on the crank sensor. But DON'T let a dealer fool you into thinking that a few thousand misfires a day are ok. (1 per 300 RPM? You do the math on that one.) THAT is what can KILL a motor. Those ALUMINUM ALLOY pistons won't tollerate mis-fires, ESPECIALLY PRE-IGNITION. Is is firing early, random? Or late?(doubling?) This would be my concern is the "when" here. They should be able to tell you that much. and that might help tell you where to start looking too.....Just MY .02 worth......

 

[Guest]

Page 102 of my OM states that long periods of idling can cause excessive exhaust temperatures which can damage your vehicle.
MD emissions test uses a treadmill which simulates city and highway conditions.
And rather than waste gas, cold climate folks should invest in an engine block heater.