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Old 06-07-2010, 02:46 PM   #1
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'01 4L hesitation problem

Problem:
I am experiencing multiple hesitations/hiccups mostly when accelerating but also when I let up on the gas after driving at a constant speed. It has happened any time but is worse when the engine is cold, especially in colder weather (40 degrees and less). Gets better as the enging warms up and then occasionally occurs. No engine indicator lights are triggered during the hesitations. Jeep hads over 125,000 miles.
What I've done so far:
  1. Replaced injectors
  2. Replaced fuel pump module (includes regulator and filter)
  3. Replaced MAP sensor
  4. Tested with my Unichip performance chip removed
  5. Rested with air filter off
Within the last couple of years, these have been replaced:
  1. Throttle position sensor
  2. Coil rail
  3. Spark plugs
Any knowledgeable ideas would be greatly appreciated...this has been bugging me for over 6 months and is getting worse not to mention the cost associated with my approach to replacing parts (but those parts had lotsa miles on them so it's not all bad).

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Old 06-07-2010, 02:57 PM   #2
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Welcome to the Forum!

Couple things come to mind, first, for the price- replace your spark plugs. Then, replace the distributor cap and rotor. When they start to go bad, they'll cause the same type of grief. Hell, replace the cap and rotor first before buying plugs if you want to. They shoud'nt be to expensive and are designed to wear out over time.

Second, if its not a spark problem you may have some water in the gas or even something as simple as dirty battery terminals. Dirty terminal connections will cause a loss of power to the throttle body, even when running and cause your same symptoms.

but, by far, start with your cap and rotor... if you've never changed one out, its best to leave the plug wires on, pull the cap off, put the new rotor in, put the new cap on then move the wires one by one from the old cap to the new to ensure you do not mix up your firing order.

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Old 06-07-2010, 04:39 PM   #3
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Quote:
Originally Posted by sevenservices View Post
Welcome to the Forum!

Couple things come to mind, first, for the price- replace your spark plugs. Then, replace the distributor cap and rotor. When they start to go bad, they'll cause the same type of grief. Hell, replace the cap and rotor first before buying plugs if you want to. They shoud'nt be to expensive and are designed to wear out over time.

Second, if its not a spark problem you may have some water in the gas or even something as simple as dirty battery terminals. Dirty terminal connections will cause a loss of power to the throttle body, even when running and cause your same symptoms.

but, by far, start with your cap and rotor... if you've never changed one out, its best to leave the plug wires on, pull the cap off, put the new rotor in, put the new cap on then move the wires one by one from the old cap to the new to ensure you do not mix up your firing order.
Thanks for the info Chris but I'm pretty sure my '01 has no distributor...has no plug wires, has a coil rail to distribute the spark.
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Old 06-07-2010, 07:12 PM   #4
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Originally Posted by sjb View Post
... I'm pretty sure my '01 has no distributor...has no plug wires, has a coil rail to distribute the spark.
You are correct.

After replacing the obvious as you have already done, I would probably next suspect one or both of the two upstream 02 sensors. They are responsible for setting the air fuel mixture which can cause all kinds of hard to diagnose engine problems.
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Old 06-07-2010, 09:51 PM   #5
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A shot in the dark -- The spark plugs - did you use the ones that the underhood label says to use, or did you fall for what the parts kids said to use?

Reason that's on my mind - I heard of another neighbor today that fried his engine with Splitfires. The neighbor behind me fried his with Splitfires last month, and he's still swapping in another engine.
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Old 06-07-2010, 11:12 PM   #6
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Just for those who don't know, 2000-2006 TJs don't have caps or rotors.
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Old 06-07-2010, 11:13 PM   #7
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just for those who don't know, 2000-2006 tjs don't have caps or rotors.
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Old 06-08-2010, 12:52 PM   #8
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Originally Posted by rrich View Post
A shot in the dark -- The spark plugs - did you use the ones that the underhood label says to use, or did you fall for what the parts kids said to use?

Reason that's on my mind - I heard of another neighbor today that fried his engine with Splitfires. The neighbor behind me fried his with Splitfires last month, and he's still swapping in another engine.
Interesting....I think I do have some non-standard plugs in there that I put in a couple of years ago. Between replacing those and the O2 sensors hopefully I can get to the bottom of this problem.
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Old 06-08-2010, 01:34 PM   #9
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Why do people think that an ex hamburger flipper that's worked at a parts house for 3 weeks knows more than the engineers that designed the heads and called out the plug to use?

I guess that's why we are in trouble now - they can vote!

Pull out a plug to check, then get the recommended ones - recommended by Jeep (they put it right on the underhood label,) not the underwear salesman at JC Pennys.

Let us know.
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Old 06-08-2010, 02:18 PM   #10
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Quote:
Originally Posted by rrich View Post
Why do people think that an ex hamburger flipper that's worked at a parts house for 3 weeks knows more than the engineers that designed the heads and called out the plug to use?

I guess that's why we are in trouble now - they can vote!

Pull out a plug to check, then get the recommended ones - recommended by Jeep (they put it right on the underhood label,) not the underwear salesman at JC Pennys.

Let us know.
I generally agree with you but by that logic I guess I shouldn't have put in a cold air intake, K&N air filter, a performance chip, etc. I understand your point and if this turns out to be the problem, I will think twice before buying into the hype from the hamburger flipper at the parts warehouse.
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Old 06-08-2010, 02:31 PM   #11
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By anyone's logic it would be better to avoid installing a cold air intake, K&N (ESPECIALLY the K&N!), and performance chip.
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Old 06-08-2010, 02:37 PM   #12
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Well I know this is getting off subject but it was my understanding that those were all good upgrades. I'm by no means an engine geek but I'd be interested in why those should be avoided. Is any engine modification a good thing in your book?
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Old 06-08-2010, 02:46 PM   #13
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Some engine mods are fine but meaningful torque/hp boosts aren't easily or inexpensively accomplished where the old 4.0L engine is concerned.

The K&N is frowned on for a few reasons... 1) It is a poor air filter at best, it's like a screen door that only keeps the larger particulates out. Filter tests at labs confirm that. 2) Its added air flow is a moot point because even the factory paper air filter has enough surface area to flow without restriction. Yes, that is true. I removed my K&N years ago when I discovered how much of my local desert dust & silica was making it past the K&N and into my engine.

So-called "performance" chips only really advance the timing a bit. By federal EPA law, they are only allowed to do even that at wide-open throttle and extremely high engine rpms. So during normal driving and offroading, they do nothing. And they will cause an engine to ping when they do start working unless you are running high octane fuel. Chips like that might help at the drag strip but that's really it... few drive their Jeeps like they're at the drag strip.

CAI systems work well on some vehicles by removing restrictions and theoretically improving power by supplying cooler (which is denser) air. But on the TJ, its air intake is already very free breathing without restrictions like some factory air intakes have had added purposely by the factory. The Mustang 5.0L engine is a prime example of a vehicle with a restrictive factory air intake system that can benefit from a free-er flowing air intake system. The TJ's was specifically designed to be free breathing without restrictions so it won't benefit from that type of air intake system.

The TJ's 4.0L is an old-school OHV system that just doesn't benefit from all the little mods like some throw at them. Lots of engines including the little Asian engines do, just not the 4.0L.
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Old 06-08-2010, 02:58 PM   #14
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Good stuff Jerry! Thanks for taking the time to educate me! With so much going on in life, I find it hard to thoroughly research all this stuff and buy into the hype more than I should. Guess that's the beauty of forums.
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Old 06-08-2010, 03:06 PM   #15
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good point on the cap and rotor, if those can be ruled out, replace your plugs for sure. They're usually the first to go and cause your symptoms. Sometimes I've seen 'em last for years, then again I've seen them foul after less than a month because of mods changing their enviroment. Some are just plain crap off the shelf...
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Old 06-08-2010, 07:30 PM   #16
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Interesting....I think I do have some non-standard plugs in there that I put in a couple of years ago. Between replacing those and the O2 sensors hopefully I can get to the bottom of this problem.
Well the spark plugs have been eliminated as the source of the problem. Replace the non-standard plugs (Bosch Platinum 4) with standard Mopar plugs and the problem still remains...no change in behavior.

I'm starting to lean towards taking the damn thing into a dealer and having the problem at least diagnosed and based on that decide whether or not to do the work myself or have them do it.

The problem is also getting worse...to the point I'm afraid it could damage the engine.
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Old 08-03-2010, 10:51 AM   #17
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UPDATE...finally took the Jeep into the dealer and they scoped the engine and found nothing wrong. Turns out to be the clutch "chattering" which seems to make sense since there was no engine codes. About 3 and a half years ago, I had a transmission problem I fixed and decided to replace the clutch and turn the flywheel since I had everything torn apart. I put in a higher end Sach clutch and have never liked how sensitive it was. It will be replaced with an OEM clutch now.

Thanks to everyone that offered advice!
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Old 02-01-2011, 06:16 AM   #18
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Quote:
Originally Posted by sjb
Problem:
I am experiencing multiple hesitations/hiccups mostly when accelerating but also when I let up on the gas after driving at a constant speed. It has happened any time but is worse when the engine is cold, especially in colder weather (40 degrees and less). Gets better as the enging warms up and then occasionally occurs. No engine indicator lights are triggered during the hesitations. Jeep hads over 125,000 miles.

What I've done so far:
[*]Replaced injectors[*]Replaced fuel pump module (includes regulator and filter)[*]Replaced MAP sensor[*]Tested with my Unichip performance chip removed[*]Rested with air filter off


Within the last couple of years, these have been replaced:
[*]Throttle position sensor[*]Coil rail[*]Spark plugs


Any knowledgeable ideas would be greatly appreciated...this has been bugging me for over 6 months and is getting worse not to mention the cost associated with my approach to replacing parts (but those parts had lotsa miles on them so it's not all bad).
Hi Guys,

I have a 1999 TJ, recently I have encountered the same "Fuel Hesitation" as mentioned within this forum. So far I have replaced a cracked Exhaust Manifold which reduced the severity of the hesitation issue but didn't eliminate it. My mechanic now informs me that the pressure in the fuel line is low on start-up but improves after a few minutes operation (and after the fuel hesitation has sorted itself out). I was planning to replace the Fuel Pump Module but beforehand, thanks to the member's comments in this thread, I shall check the battery and replace the Distributor Cap, Rotor, Spark Plugs and Leads. Is there any particular brand of Fuel Pump Module you guys recommend? (Crown, Airtex, Carter, ?).

Thanks
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Old 02-01-2011, 06:24 AM   #19
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Ultimately my problem came down to a bad third party throttle position sensor...didn't figure that since I had replaced. I replaced it with and OEM part and haven't had a problem since. As for the fuel pump module, went with OEM product...I've turned pretty cold on third party parts......

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