rough idle question
02-19-2009, 08:33 PM
#11
JK Enthusiast
Thread Starter
i mostly notice it after it's already warmed up. it kinda feels like the engine will shake every few seconds. i opened the hood and watched it and it looked like the engine would almost jerk when it did it. when i'm inside i can feel it through the seat and the shifter.
thanks for your reply
thanks for your reply
02-19-2009, 08:35 PM
#12
JK Enthusiast
Thread Starter
Yeah, P0306 is a "cylinder 6 misfire". Apart from injector or computer problems, could be your plug/coil connections that are loose/faulty.
Was doing some offroading on bumpy & muddy terrain in the wet & had a miss on idle the next day on start-up. Threw up a cylinder 2 misfire code on mine, so pullled the plug & coil cables which were wet & muddy & a little loose, dried them out (wife's hairdryer), plugged it back in & it's been fine ever since.
Was doing some offroading on bumpy & muddy terrain in the wet & had a miss on idle the next day on start-up. Threw up a cylinder 2 misfire code on mine, so pullled the plug & coil cables which were wet & muddy & a little loose, dried them out (wife's hairdryer), plugged it back in & it's been fine ever since.
thanks for your reply
02-20-2009, 03:20 PM
#13
JK Newbie
Join Date: Feb 2009
Location: Highlands Ranch, CO
Posts: 87
Likes: 0
Received 0 Likes
on
0 Posts
I got mine back from the dealership. As cmpmacchia stated and now my mechanic, these V6 engines rough idle is normal. I pointed out that my wifes JK Unlimited '07 (which as far as I know has the same engine) does not have this issue. He shrugged his shoulders and said, "then we may see a tsb real soon."
All I can suggest is that you push your Service Manager to file a complaint in a hope that Jeep will recognize this as a problem and act on it...otherwise I guess we will just have to live with it.
All I can suggest is that you push your Service Manager to file a complaint in a hope that Jeep will recognize this as a problem and act on it...otherwise I guess we will just have to live with it.
02-20-2009, 04:29 PM
#15
JK Newbie
Join Date: Sep 2008
Location: US
Posts: 53
Likes: 0
Received 0 Likes
on
0 Posts
Here is how the PCode P030x Misfire sets:
The misfire detection algoritm monitors the crankshaft sensor signal for drops in acceleration when an acceleration is expected - i.e at 6 points in the operating cycle (2 revs of the crankshaft) when the fuel i expected to combust for each cylinder, force the piston downwards and accelertates the crankshaft. Then, put simply, when the accleration is below a threshold a misfire 'count' is incremented for that cylinder inside the ECUs SW.
When the counts exceed a threshold for every 200 engine cycles for a cylinder, then a P030x (x being cyl number) will set and the MIL will flash as long as misfire is detected - to warn of catalyst damaging operating condition (i.e. let off the gas and ease stress on engine or you cat or exhaust side of engine will over temp). MIL will remain steady lit until 4 trips pass without the misfire threshold being detected.
Similarly when the counts exceed a different, lower, threshold for every 1000 engine cycles for a cylinder, then a P030x (x being cyl number) will also set and the MIL will illuminate to indicate that misfire has occured to an extent that emissions are impacted above the certified threshold.
Bottom Line - P030x will non set unless combustion persistently aint correct.
When you get annoying midfire at idle and no PCode, the misfire count may be increasing, but not significant enough in any 200 or 1000 cycle to trigger the PCode. You should ask the dealer to connect StarScan and monitor misfire counts by cylinder to prove you have an issue and identify the cylinder(s).
Similarly the combustion may be poor, but not enough of a poor acceleration to trigger the misfire count to increase...you've just got to attack the obvious.
The thing is it can be so random, what can you prove as root casue - design/manufacture/weather/fuel/..?
What can cause misfire?
A million things......includng crap in engines during manufacture.
Easy to try:
Different brand of fuel
- run-empty current tank and try a quality brand like Shell, BP.
Try a different Octane of fuel - a little far fetched in idle where max spark advance is not typicaly applied, but somtimes it does the magic
- again, empty current tank and try with a new tank of the new stuff
Different blend of fuel
- fuel blends change all year round although people often refer to winter and summer blends. The refiners make them more or less volatile to aid starting (more volatile in the cold winter, less volatile in the hot summers).
- in transition times (e.g. between real winter and warm spring, or if weather is mis-behaving from it's average from the region you buy the fuel) fuel blends can be mismatched and some engines can be especially sensitive in idle.
- you can't fix this (unless you try a vendor from different refiner who is significantly different), but keep monitoring as season progresses.
Switch out spark plugs and check condition of old ones (cheap try).
You can get/ask for the injectors flow tested and cleaned - not sure if dealers do this anymore.
Dealer may be able to do a injector test/cylinder balance check via StarScan (without removing injectors)
Check HT leads for good connections.
Check Coil (not sure how..)
Check compression of each cylinder.
The misfire detection algoritm monitors the crankshaft sensor signal for drops in acceleration when an acceleration is expected - i.e at 6 points in the operating cycle (2 revs of the crankshaft) when the fuel i expected to combust for each cylinder, force the piston downwards and accelertates the crankshaft. Then, put simply, when the accleration is below a threshold a misfire 'count' is incremented for that cylinder inside the ECUs SW.
When the counts exceed a threshold for every 200 engine cycles for a cylinder, then a P030x (x being cyl number) will set and the MIL will flash as long as misfire is detected - to warn of catalyst damaging operating condition (i.e. let off the gas and ease stress on engine or you cat or exhaust side of engine will over temp). MIL will remain steady lit until 4 trips pass without the misfire threshold being detected.
Similarly when the counts exceed a different, lower, threshold for every 1000 engine cycles for a cylinder, then a P030x (x being cyl number) will also set and the MIL will illuminate to indicate that misfire has occured to an extent that emissions are impacted above the certified threshold.
Bottom Line - P030x will non set unless combustion persistently aint correct.
When you get annoying midfire at idle and no PCode, the misfire count may be increasing, but not significant enough in any 200 or 1000 cycle to trigger the PCode. You should ask the dealer to connect StarScan and monitor misfire counts by cylinder to prove you have an issue and identify the cylinder(s).
Similarly the combustion may be poor, but not enough of a poor acceleration to trigger the misfire count to increase...you've just got to attack the obvious.
The thing is it can be so random, what can you prove as root casue - design/manufacture/weather/fuel/..?
What can cause misfire?
A million things......includng crap in engines during manufacture.
Easy to try:
Different brand of fuel
- run-empty current tank and try a quality brand like Shell, BP.
Try a different Octane of fuel - a little far fetched in idle where max spark advance is not typicaly applied, but somtimes it does the magic
- again, empty current tank and try with a new tank of the new stuff
Different blend of fuel
- fuel blends change all year round although people often refer to winter and summer blends. The refiners make them more or less volatile to aid starting (more volatile in the cold winter, less volatile in the hot summers).
- in transition times (e.g. between real winter and warm spring, or if weather is mis-behaving from it's average from the region you buy the fuel) fuel blends can be mismatched and some engines can be especially sensitive in idle.
- you can't fix this (unless you try a vendor from different refiner who is significantly different), but keep monitoring as season progresses.
Switch out spark plugs and check condition of old ones (cheap try).
You can get/ask for the injectors flow tested and cleaned - not sure if dealers do this anymore.
Dealer may be able to do a injector test/cylinder balance check via StarScan (without removing injectors)
Check HT leads for good connections.
Check Coil (not sure how..)
Check compression of each cylinder.
Last edited by foxcasper; 02-20-2009 at 04:49 PM.
02-21-2009, 02:58 PM
#16
JK Enthusiast
Thread Starter
first off, thanks to everyone who responded.
i put in the injector cleaner the service manager gave me and it solved the problem. no more rough idle. but now i can really hear the valves rattling. maybe just cheap gas...haha.
thanks everyone!
i put in the injector cleaner the service manager gave me and it solved the problem. no more rough idle. but now i can really hear the valves rattling. maybe just cheap gas...haha.
thanks everyone!