Hesitation/misfire under load after sitting over night

JayKay

JayKay

Caught the Bug
I have a 2012 JKUS manual, been dealing with a hesitation after cold soak during cold ambient temperatures (50 degrees Fahrenheit or less). The hesitation is almost violent when it happens, almost as if the engine is shut off and turned back on. There is no MIL illuminated. Dealer has done two updated PCM flashes, saying it should fix it, but so far it hasn't. Anyone dealing with or experience the same issue?
 
gtony12

gtony12

Caught the Bug
I have a similar hesitation when cold first start up in morning time not super bad but going away few minutes later. Not sure if this is normal or not or if the same as your jeep.

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jku_robert

jku_robert

New member
JeepKeeper said:
I have a 2012 JKUS manual, been dealing with a hesitation after cold soak during cold ambient temperatures (50 degrees Fahrenheit or less). The hesitation is almost violent when it happens, almost as if the engine is shut off and turned back on. There is no MIL illuminated. Dealer has done two updated PCM flashes, saying it should fix it, but so far it hasn't. Anyone dealing with or experience the same issue?
Click to expand...

How many miles?

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JayKay

JayKay

Caught the Bug
jku_robert said:
How many miles?

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27,000 now, noticed the issue back when it had probably 3,000. It's just not something that makes the jeep impossible to drive, just an annoyance. The problem has been looked into 2 or 3 times with either the "it's normal" response or "we updated the PCM, that should fix it" response. Had it at the dealer today and they flashed the PCM again, haven't driven it since, guess I'll find out what it does in the morning.
 
jeeeep

jeeeep

Hooked
my 2010 would do that after sitting for several days, I replaced the plugs, coils and wires with performance distributors screamin demon coil and wires - haven't had any issues since.
also uses autolite platinum plugs, IMO worth the price and best performance upgrade I've done
 
JayKay

JayKay

Caught the Bug
jeeeep said:
my 2010 would do that after sitting for several days, I replaced the plugs, coils and wires with performance distributors screamin demon coil and wires - haven't had any issues since.
also uses autolite platinum plugs, IMO worth the price and best performance upgrade I've done
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Thanks for the input, but I'm sure that's not the type of problem I'm having. Since my odometer is at 27,000, it's hard for me to believe I would have bad ignition parts already. The way it acts is like it's got a slow or bad signal from the accelerator pedal to the throttle body, especially since the 3.6 is fly-by-wire. I would think if I had a bad coil or plug I'd have a misfire code and the issue would occur more often. Got home from the dealer 15 minutes ago and it didn't do it at all before it warmed up. We'll see what it does in the morning.
 
txjeeplover

txjeeplover

Member
I developed this very same minor issue on my 2008 3.8 liter this week! I'm at 120k miles and my wires and spark plugs have just under 20k miles. I'm going to swap out the ignition coil and replace the purge valve and leak detection sensor. In my situation, I suspect that it's my 120k mile ignition coil. I get the gas cap warning light at least once a month despite having replaced multiple caps, so part of me thinks it could also be related to a momentary poor air/fuel mixture at start-up.
 
David1tontj

David1tontj

New member
I think you might be onto something with the poor air fuel ratio.. I won't claim to be an expert on this, but I do know a couple basics... Before a rig warms up, it runs on an open loop, meaning that it doesn't take any info from your o2 sensors, MAF, etc. to adjust the ratio.

I'm Not really sure on what would cause it to run that poorly on the computers default program...

I'm sure someone else will weigh in...

Does this only happen when under load, or does it happen in neutral too?




My ride- 2001 power wheel, 11" plastic tires, upgraded battery, boat sides, custom bumpers, tow hooks, new paint.
 
JayKay

JayKay

Caught the Bug
David1tontj said:
I think you might be onto something with the poor air fuel ratio.. I won't claim to be an expert on this, but I do know a couple basics... Before a rig warms up, it runs on an open loop, meaning that it doesn't take any info from your o2 sensors, MAF, etc. to adjust the ratio.

I'm Not really sure on what would cause it to run that poorly on the computers default program...

I'm sure someone else will weigh in...

Does this only happen when under load, or does it happen in neutral too?




My ride- 2001 power wheel, 11" plastic tires, upgraded battery, boat sides, custom bumpers, tow hooks, new paint.
Click to expand...

I seem to notice it more on my '12 when pulling out of my driveway and headed up the street in the morning. The street in front of the house is a slightly uphill for a block or so. It is noticeable at 1/4 to 1/2 throttle in 1st gear and 2nd. Going uphill makes me consider it being under the load of its own weight, plus turning 35s.
 
JayKay

JayKay

Caught the Bug
jku_robert said:
Almost sounds like a coil

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Click to expand...

You know, that's the way it feels to me. I work in an independent automotive and tire shop. We see all the Ford 4.6 and 5.4s come in with bad coils (very common on those engines) 99% of them have the MIL lit and numerous misfire codes. Most of the time they act up when the engine is hot. My 3.6 only seems to do it when the engine is cold, especially after sitting over night or during the day while I'm at work. I'll see if maybe I can talk the dealership into hooking it up to the lab scope and seeing if there's any history misfires in the PCM. I'm sure as hell not gonna do it, it's under warranty:)
 
jku_robert

jku_robert

New member
It sucks that the dealership can't figure it out makes you kinda question the technicians

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JayKay

JayKay

Caught the Bug
jku_robert said:
It sucks that the dealership can't figure it out makes you kinda question the technicians

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Especially aggravating when you get a call after they've only had it for two hours saying it's done. Really?!?! Guess I'll have to take him for a ride and describe what it's doing when it's doing it. Ugh!
 
jku_robert

jku_robert

New member
I work at Audi and it sounds kinda corny but I take pride in my work and make sure the car gets fixed THE FIRST TIME.

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JayKay

JayKay

Caught the Bug
jku_robert said:
I work at Audi and it sounds kinda corny but I take pride in my work and make sure the car gets fixed THE FIRST TIME.

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I'm with you on that one. I worked at a Ford dealer and understand how the warranty works. The manufacturer tells the tech to do this, if that doesn't work, do this, if that still doesn't take care of the problem, then replace this. Well my jeep has been in for the same problem twice, two PCM updates later, I'm not sure if it's gonna fix it since the first update didn't.
 
jku_robert

jku_robert

New member
JeepKeeper said:
I'm with you on that one. I worked at a Ford dealer and understand how the warranty works. The manufacturer tells the tech to do this, if that doesn't work, do this, if that still doesn't take care of the problem, then replace this. Well my jeep has been in for the same problem twice, two PCM updates later, I'm not sure if it's gonna fix it since the first update didn't.
Click to expand...

Well let us know what happens. I'm interested to see what they find.

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txjeeplover

txjeeplover

Member
For what it's worth, my misfire and hesitation suddenly got worse yesterday and I got DTC P0302. I changed the coil pack, the wires, and the plugs which fixed the problem.
 
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