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I didn't think of it, but could this issue too be related?

Usually after a period of sitting (classes for say 8 hours or whatnot) and I pull out, sometimes if I go to get on it a little to get in front of traffic, the jeep will stumble/hesitate (think of a carbureted car w/no choke and not warmed up, the stumble you get if you nail it too hard).

I always thought it was ESP kicking in, but I looked down after it did it pulling out of work yesterday (Jeep sat 5 hours) and no ESP light came on. It takes off like a m_ther__cker after it stumbles, but there is indeed a second or so delay where it just doesn't move.

Could it all be fuel-pressure related? Again, every time its hesitated, the jeep has sat for a few hours, and it's only when the jeep demands higher fuel pressure (i.e. trying to pass traffic, pull out into traffic, or whatnot). Only problem is that this problem is very random. The 5-6 (?) months I've had the jeep, its done it maybe 6-10 times.

Author:	07Latitude [ Sun Apr 08, 2007 11:42 am ]
Post subject:	Cold start
Ok guys, here's the latest oddity with my 07. The weather here in MI has gone from 60-70 degree mornings, to 20-30 degree mornings with Snow. The first cold day we had here is when the issue began. Upon cold (sitting overnight) startup, the vehicle sputters to start up. Usually, the jeep ALWAYS starts r-r-r-Vroom. Now, it's r-r-r-sputter-Vroom, like it's struggling to actually fire. It cranks over the same "3 times" i suppose you could say, but I get what almost mimics the starter turning a motor that's ALMOST firing for a split second, then the motor finally kicks over. If the vehicle sits 5-6 hours, it starts fine. Heck, shutting it off after 15 seconds after first morning start yields another perfect restart. I was at the girlfriends and it sat 8.5 hours. It only mildly had its startup issue. But any sitting longer than that, and the issue occurs. Could the computer have adapted to warm weather starting and is having trouble with the sudden cold (say, wrong mixture or something)? What else could cause this? My luck would be the dealer would get it, let it sit, and it'll warm up outside and the problem will go away. I don't know for sure if its only cold weather related, but it started with the temp change here. Throw some ideas out there guys. I believe the PCM is in "open loop" that the problem occurs, correct?

Author:	myjeepwalks [ Sun Apr 08, 2007 11:56 am ]
Post subject:
Almost sounds like the fuel pump is not holding pressure. After it sits for a while the pressure is leaking down. I used to work for Ford and their fuel pumps used to be the cause of exactly what you are describing. Not sure if the kj fuel pump is similar. Just a thought.

Author:	07Latitude [ Sun Apr 08, 2007 12:07 pm ]
Post subject:
I too thought of that. I've wanted to see if it is a consistently occurring problem, but also have wanted to try key-on for a few secs to prime the system prior to startup. Maybe I'll cold-start it sometime today and see if it does it again. If it does, then I'll try priming the system before cranking the next morning and see if that helps.

Author:	07Latitude [ Sun Apr 08, 2007 12:12 pm ]
Post subject:
I didn't think of it, but could this issue too be related? Usually after a period of sitting (classes for say 8 hours or whatnot) and I pull out, sometimes if I go to get on it a little to get in front of traffic, the jeep will stumble/hesitate (think of a carbureted car w/no choke and not warmed up, the stumble you get if you nail it too hard). I always thought it was ESP kicking in, but I looked down after it did it pulling out of work yesterday (Jeep sat 5 hours) and no ESP light came on. It takes off like a m_ther__cker after it stumbles, but there is indeed a second or so delay where it just doesn't move. Could it all be fuel-pressure related? Again, every time its hesitated, the jeep has sat for a few hours, and it's only when the jeep demands higher fuel pressure (i.e. trying to pass traffic, pull out into traffic, or whatnot). Only problem is that this problem is very random. The 5-6 (?) months I've had the jeep, its done it maybe 6-10 times.

Author:	tjkoen01 [ Sun Apr 08, 2007 9:57 pm ]
Post subject:
07Latitude wrote: I didn't think of it, but could this issue too be related? Usually after a period of sitting (classes for say 8 hours or whatnot) and I pull out, sometimes if I go to get on it a little to get in front of traffic, the jeep will stumble/hesitate (think of a carbureted car w/no choke and not warmed up, the stumble you get if you nail it too hard). I always thought it was ESP kicking in, but I looked down after it did it pulling out of work yesterday (Jeep sat 5 hours) and no ESP light came on. It takes off like a m_ther__cker after it stumbles, but there is indeed a second or so delay where it just doesn't move. Could it all be fuel-pressure related? Again, every time its hesitated, the jeep has sat for a few hours, and it's only when the jeep demands higher fuel pressure (i.e. trying to pass traffic, pull out into traffic, or whatnot). Only problem is that this problem is very random. The 5-6 (?) months I've had the jeep, its done it maybe 6-10 times. you might have 2 problems. my 96 zj did the stumbling thing like you describe. it didn't happen all the time, and when it did happen, it would only do it one time shortly after starting. it took me awhile to track it down with my CarChip, but it was one of the O2 sensors sending out a voltage spike causing the computer to think it was running rich, so it would lean out the A/F ratio by cutting back the fuel. the reason it only did it once was b/c it was related to the heater on the O2 sensor heating it up and the transition from open loop to closed loop control in the computer.....and no, it did not throw any codes.

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