There is a TSB that addresses this problem. Short and sweet version: Carbon
buildup that causes exhaust valves to be "slow to close".

In message <78db4679.0401300617.10547938@posting.google.com >, "Pat" wrote:

>I have a 2003 Jeep Grand Cherokee that misfires really bad when
>certain conditions exsist. I know that if I accelerate going up a
>steep hill - the motor misfires so bad that it is like a bucking
>horse.
>
>I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
>and replaced it, after numerous attempts to fix the problem, and now
>the 2nd Jeep does the SAME EXACT THING.
>
>My dealership tells me that Jeep Hot Line doesn't have any reports
>about this problem from anyone else. My dealership is going to put a
>co-pilot on my Jeep to get better computer codes. All they know is
>that there is a misfire. And as luck would have it - the mechanic can
>not reproduce the problem.
>
>The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
>miles when I got swapped it out for a different Jeep. This 2nd Jeep
>was brand new as well and at 23,000 miles at the same exact location
>as one of the previous misfires, it started misfiring. I
>was going 55 mph about 100 miles from home on my way to a relative's
>house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
>The
>car has had gas from various gas stations during the misfires so I
>don't
>think the problem is specific to the gasoline that it is using. But
>in this case I had bought gas (filled up) at a Shell station about 50
>miles before the misfire.
>
>Most recently, I was going up a hill on the interstate trying to pass
>a semi and when it kicked into passing gear -bingo, it started
>misfiring so bad I had
>to pull over.
>
>After turning off the Jeep for about 15 minutes, I restarted the Jeep
>it ran smoothly but the check engine light was on.
>
>It does not matter if it is cold or warm out. It does not matter if I
>have gone 1 mile or 100 miles - the only consistent thing that I can
>find is that both vehicles are 2003 Jeep Grand Cherokees and that I
>was either accelerating or on a highway at highway speeds.
>
>The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
>Jeep, the dealership reset the magentic pickup - then replaced it -
>then gave up.
>
>Thanks in advance so much for suggestions and help.
>
>Pat

 

There is a TSB that addresses this problem. Short and sweet version: Carbon
buildup that causes exhaust valves to be "slow to close".

In message <78db4679.0401300617.10547938@posting.google.com >, "Pat" wrote:

>I have a 2003 Jeep Grand Cherokee that misfires really bad when
>certain conditions exsist. I know that if I accelerate going up a
>steep hill - the motor misfires so bad that it is like a bucking
>horse.
>
>I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
>and replaced it, after numerous attempts to fix the problem, and now
>the 2nd Jeep does the SAME EXACT THING.
>
>My dealership tells me that Jeep Hot Line doesn't have any reports
>about this problem from anyone else. My dealership is going to put a
>co-pilot on my Jeep to get better computer codes. All they know is
>that there is a misfire. And as luck would have it - the mechanic can
>not reproduce the problem.
>
>The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
>miles when I got swapped it out for a different Jeep. This 2nd Jeep
>was brand new as well and at 23,000 miles at the same exact location
>as one of the previous misfires, it started misfiring. I
>was going 55 mph about 100 miles from home on my way to a relative's
>house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
>The
>car has had gas from various gas stations during the misfires so I
>don't
>think the problem is specific to the gasoline that it is using. But
>in this case I had bought gas (filled up) at a Shell station about 50
>miles before the misfire.
>
>Most recently, I was going up a hill on the interstate trying to pass
>a semi and when it kicked into passing gear -bingo, it started
>misfiring so bad I had
>to pull over.
>
>After turning off the Jeep for about 15 minutes, I restarted the Jeep
>it ran smoothly but the check engine light was on.
>
>It does not matter if it is cold or warm out. It does not matter if I
>have gone 1 mile or 100 miles - the only consistent thing that I can
>find is that both vehicles are 2003 Jeep Grand Cherokees and that I
>was either accelerating or on a highway at highway speeds.
>
>The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
>Jeep, the dealership reset the magentic pickup - then replaced it -
>then gave up.
>
>Thanks in advance so much for suggestions and help.
>
>Pat

 

There is a TSB that addresses this problem. Short and sweet version: Carbon
buildup that causes exhaust valves to be "slow to close".

In message <78db4679.0401300617.10547938@posting.google.com >, "Pat" wrote:

>I have a 2003 Jeep Grand Cherokee that misfires really bad when
>certain conditions exsist. I know that if I accelerate going up a
>steep hill - the motor misfires so bad that it is like a bucking
>horse.
>
>I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
>and replaced it, after numerous attempts to fix the problem, and now
>the 2nd Jeep does the SAME EXACT THING.
>
>My dealership tells me that Jeep Hot Line doesn't have any reports
>about this problem from anyone else. My dealership is going to put a
>co-pilot on my Jeep to get better computer codes. All they know is
>that there is a misfire. And as luck would have it - the mechanic can
>not reproduce the problem.
>
>The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
>miles when I got swapped it out for a different Jeep. This 2nd Jeep
>was brand new as well and at 23,000 miles at the same exact location
>as one of the previous misfires, it started misfiring. I
>was going 55 mph about 100 miles from home on my way to a relative's
>house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
>The
>car has had gas from various gas stations during the misfires so I
>don't
>think the problem is specific to the gasoline that it is using. But
>in this case I had bought gas (filled up) at a Shell station about 50
>miles before the misfire.
>
>Most recently, I was going up a hill on the interstate trying to pass
>a semi and when it kicked into passing gear -bingo, it started
>misfiring so bad I had
>to pull over.
>
>After turning off the Jeep for about 15 minutes, I restarted the Jeep
>it ran smoothly but the check engine light was on.
>
>It does not matter if it is cold or warm out. It does not matter if I
>have gone 1 mile or 100 miles - the only consistent thing that I can
>find is that both vehicles are 2003 Jeep Grand Cherokees and that I
>was either accelerating or on a highway at highway speeds.
>
>The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
>Jeep, the dealership reset the magentic pickup - then replaced it -
>then gave up.
>
>Thanks in advance so much for suggestions and help.
>
>Pat

 

Check your manual. It'll tell you, you can't use high octane fuel. Although I
don't understand why.... Most new 4.0L Grand Cherokees require 87 Octane. If
you put in 93 octane, it'll hesitate and set the check engine light off. Then
you bring it to the dealership and.... $132 later you have a new spakplug,
because the old one misfired. It cost $82 just to plug the Jeep into the
computer!

 

Check your manual. It'll tell you, you can't use high octane fuel. Although I
don't understand why.... Most new 4.0L Grand Cherokees require 87 Octane. If
you put in 93 octane, it'll hesitate and set the check engine light off. Then
you bring it to the dealership and.... $132 later you have a new spakplug,
because the old one misfired. It cost $82 just to plug the Jeep into the
computer!

 

Check your manual. It'll tell you, you can't use high octane fuel. Although I
don't understand why.... Most new 4.0L Grand Cherokees require 87 Octane. If
you put in 93 octane, it'll hesitate and set the check engine light off. Then
you bring it to the dealership and.... $132 later you have a new spakplug,
because the old one misfired. It cost $82 just to plug the Jeep into the
computer!

 

Pat what you might have is a bad TPS. "Throttle position sensor". Because
you say when you accelerate it happens, and it sounds like your mechanic is
not finding any "DTC's" or diagnostic codes relating to the problem. For
example if there was a P0303 code it would indiacte #3 cylinder misfire and
your dealer could go from there. I have seen this same problem before.
Chrysler told us at the dealership I work for that the "DRB" which is the
hand held scan tool we use the diagnose problems is to slow to see the
inconsistency of the TPS when you move the throttle plate. When you
accelerate you move the TPS the "PCM" power control module sees this
inconsistency and leans the fuel mixture. If you dealer had contacted "STAR
ONLINE" they might have told him this. The hot line reports are some times
limited on info so your dealer should no hesitate to contact directly with
Star to help solve the problem.
Hope this helps
Mike the Jeep Mechanic

"Pat" <pat@nebraskaruralweb.com> wrote in message
news:78db4679.0401300617.10547938@posting.google.c om...
> I have a 2003 Jeep Grand Cherokee that misfires really bad when
> certain conditions exsist. I know that if I accelerate going up a
> steep hill - the motor misfires so bad that it is like a bucking
> horse.
>
> I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
> and replaced it, after numerous attempts to fix the problem, and now
> the 2nd Jeep does the SAME EXACT THING.
>
> My dealership tells me that Jeep Hot Line doesn't have any reports
> about this problem from anyone else. My dealership is going to put a
> co-pilot on my Jeep to get better computer codes. All they know is
> that there is a misfire. And as luck would have it - the mechanic can
> not reproduce the problem.
>
> The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
> miles when I got swapped it out for a different Jeep. This 2nd Jeep
> was brand new as well and at 23,000 miles at the same exact location
> as one of the previous misfires, it started misfiring. I
> was going 55 mph about 100 miles from home on my way to a relative's
> house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
> The
> car has had gas from various gas stations during the misfires so I
> don't
> think the problem is specific to the gasoline that it is using. But
> in this case I had bought gas (filled up) at a Shell station about 50
> miles before the misfire.
>
> Most recently, I was going up a hill on the interstate trying to pass
> a semi and when it kicked into passing gear -bingo, it started
> misfiring so bad I had
> to pull over.
>
> After turning off the Jeep for about 15 minutes, I restarted the Jeep
> it ran smoothly but the check engine light was on.
>
> It does not matter if it is cold or warm out. It does not matter if I
> have gone 1 mile or 100 miles - the only consistent thing that I can
> find is that both vehicles are 2003 Jeep Grand Cherokees and that I
> was either accelerating or on a highway at highway speeds.
>
> The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
> Jeep, the dealership reset the magentic pickup - then replaced it -
> then gave up.
>
> Thanks in advance so much for suggestions and help.
>
> Pat

 

Pat what you might have is a bad TPS. "Throttle position sensor". Because
you say when you accelerate it happens, and it sounds like your mechanic is
not finding any "DTC's" or diagnostic codes relating to the problem. For
example if there was a P0303 code it would indiacte #3 cylinder misfire and
your dealer could go from there. I have seen this same problem before.
Chrysler told us at the dealership I work for that the "DRB" which is the
hand held scan tool we use the diagnose problems is to slow to see the
inconsistency of the TPS when you move the throttle plate. When you
accelerate you move the TPS the "PCM" power control module sees this
inconsistency and leans the fuel mixture. If you dealer had contacted "STAR
ONLINE" they might have told him this. The hot line reports are some times
limited on info so your dealer should no hesitate to contact directly with
Star to help solve the problem.
Hope this helps
Mike the Jeep Mechanic

"Pat" <pat@nebraskaruralweb.com> wrote in message
news:78db4679.0401300617.10547938@posting.google.c om...
> I have a 2003 Jeep Grand Cherokee that misfires really bad when
> certain conditions exsist. I know that if I accelerate going up a
> steep hill - the motor misfires so bad that it is like a bucking
> horse.
>
> I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
> and replaced it, after numerous attempts to fix the problem, and now
> the 2nd Jeep does the SAME EXACT THING.
>
> My dealership tells me that Jeep Hot Line doesn't have any reports
> about this problem from anyone else. My dealership is going to put a
> co-pilot on my Jeep to get better computer codes. All they know is
> that there is a misfire. And as luck would have it - the mechanic can
> not reproduce the problem.
>
> The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
> miles when I got swapped it out for a different Jeep. This 2nd Jeep
> was brand new as well and at 23,000 miles at the same exact location
> as one of the previous misfires, it started misfiring. I
> was going 55 mph about 100 miles from home on my way to a relative's
> house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
> The
> car has had gas from various gas stations during the misfires so I
> don't
> think the problem is specific to the gasoline that it is using. But
> in this case I had bought gas (filled up) at a Shell station about 50
> miles before the misfire.
>
> Most recently, I was going up a hill on the interstate trying to pass
> a semi and when it kicked into passing gear -bingo, it started
> misfiring so bad I had
> to pull over.
>
> After turning off the Jeep for about 15 minutes, I restarted the Jeep
> it ran smoothly but the check engine light was on.
>
> It does not matter if it is cold or warm out. It does not matter if I
> have gone 1 mile or 100 miles - the only consistent thing that I can
> find is that both vehicles are 2003 Jeep Grand Cherokees and that I
> was either accelerating or on a highway at highway speeds.
>
> The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
> Jeep, the dealership reset the magentic pickup - then replaced it -
> then gave up.
>
> Thanks in advance so much for suggestions and help.
>
> Pat

 

Pat what you might have is a bad TPS. "Throttle position sensor". Because
you say when you accelerate it happens, and it sounds like your mechanic is
not finding any "DTC's" or diagnostic codes relating to the problem. For
example if there was a P0303 code it would indiacte #3 cylinder misfire and
your dealer could go from there. I have seen this same problem before.
Chrysler told us at the dealership I work for that the "DRB" which is the
hand held scan tool we use the diagnose problems is to slow to see the
inconsistency of the TPS when you move the throttle plate. When you
accelerate you move the TPS the "PCM" power control module sees this
inconsistency and leans the fuel mixture. If you dealer had contacted "STAR
ONLINE" they might have told him this. The hot line reports are some times
limited on info so your dealer should no hesitate to contact directly with
Star to help solve the problem.
Hope this helps
Mike the Jeep Mechanic

"Pat" <pat@nebraskaruralweb.com> wrote in message
news:78db4679.0401300617.10547938@posting.google.c om...
> I have a 2003 Jeep Grand Cherokee that misfires really bad when
> certain conditions exsist. I know that if I accelerate going up a
> steep hill - the motor misfires so bad that it is like a bucking
> horse.
>
> I have had 2 of these Jeeps. The dealer called my 1st Jeep a lemon
> and replaced it, after numerous attempts to fix the problem, and now
> the 2nd Jeep does the SAME EXACT THING.
>
> My dealership tells me that Jeep Hot Line doesn't have any reports
> about this problem from anyone else. My dealership is going to put a
> co-pilot on my Jeep to get better computer codes. All they know is
> that there is a misfire. And as luck would have it - the mechanic can
> not reproduce the problem.
>
> The 1st Jeep did this 3 times beginning at 3,000 miles until 10,000
> miles when I got swapped it out for a different Jeep. This 2nd Jeep
> was brand new as well and at 23,000 miles at the same exact location
> as one of the previous misfires, it started misfiring. I
> was going 55 mph about 100 miles from home on my way to a relative's
> house. The first Jeep did the EXACT SAME THING in the SAME LOCATION.
> The
> car has had gas from various gas stations during the misfires so I
> don't
> think the problem is specific to the gasoline that it is using. But
> in this case I had bought gas (filled up) at a Shell station about 50
> miles before the misfire.
>
> Most recently, I was going up a hill on the interstate trying to pass
> a semi and when it kicked into passing gear -bingo, it started
> misfiring so bad I had
> to pull over.
>
> After turning off the Jeep for about 15 minutes, I restarted the Jeep
> it ran smoothly but the check engine light was on.
>
> It does not matter if it is cold or warm out. It does not matter if I
> have gone 1 mile or 100 miles - the only consistent thing that I can
> find is that both vehicles are 2003 Jeep Grand Cherokees and that I
> was either accelerating or on a highway at highway speeds.
>
> The Jeep is a 6 cyclinder Jeep Grand Cherokee Laredo. On the 1st
> Jeep, the dealership reset the magentic pickup - then replaced it -
> then gave up.
>
> Thanks in advance so much for suggestions and help.
>
> Pat