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 Post subject: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 12:14 am 
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Location: IL
2002 Limited (V6 gas), basically stock and original. It has always gotten bad mileage (12 ish city, 20 highway) but that is with the wretched alcohol diluted gas we have to get in illannoy. With real gas its more like 13+/22, still pretty bad.

It was in for mileage several times through 2004 and had the computer reflashes done then. In the last year it had the front pipes and lower cat and the muffler replaced. In spring after running a tank with Sea Foam and doing 'the treatment' with it I replaced the PCV valve, spark plugs (with E3s that I got on sale based on numerous recommendations), an AMSoil air filter, and new thermostat (factory temp). I also replaced numerous vacuum hoses under the hood to clear an error code. Its been getting Mobil 1 for 5 years, and had its last change in late winter, currently 2800 miles ago. I did the ECU clear (pull the battery and draw down power so it resets to default and 'relearns' after doing all the maintenance work and drove it around town about 2 weeks before a 900 mile round trip.

Coolant (old and new) is clean and clear, oil is good, no sign of blow-by or leakage between oil and coolant. Trip mileage was low (16-17mpg) but I did have a Surco roof rack on it so its not representative. But now in town I'm down to 11MPG (roof rack off and lightly loaded) and there's a stumble or miss when in a high vacuum state decelerating. IOW when I let off the gas and start coasting I can hear and feel the engine stumble a bit. No problems at idle or while accelerating.

My scantool (KalEquip/Actron 9615) shows no problems, no codes. When I record a few minutes of operation (this tool can record and review but not dump to a computer) nothing looks out of bounds but I'm far from expert on that.

Tires (stock size Geolandar HTX) are at recommended pressure. I'm certain the car is not getting gas stolen, at least not on any regular basis.


Any thoughts on the deceleration stumbling, or the fuel economy appreciated. I'd love to get this Jeep up to the 15-18MPG so many report getting in town much less the mid 20s on the freeway. Would it be worth taking in for another ECU or trans controller reflash (its been 6+ years)? Could the E3 plugs be the cause of the stumbling under just that specific condition?

Rich

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2002 Liberty Limited 4WD, 3.7l V6
Steel Blue/Taupe
Selec-Trac, Offroad Group, Trailer Tow Group
1971 Dodge Challenger, 318cid, A904 Torqueflite


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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 12:30 am 
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Putting in the correct plugs would be the 1st step.Have had many complaints about the "gimmick" plugs like E3's in the last few months at work.

Also changing the diffs,t-case,trans fluids(with the correct fluids),and finally the fuel filter will help.


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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 1:23 am 
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Location: IL
Thanks. It had 'correct' replacement plugs in it from late 2006 till this past Spring; factory before that. No difference in performance or mileage for that first change. I suppose the E3s could be part of the problem (the stumble at least) but not sure since outside of that one range

I need a new fuel filter. Transmission, transfer case, and axle fluids (and trans filter) were changed about 18 months ago (~9000 miles ago in the book) and twice before at the dealership (I think in 2004 and 2008). Nothing has ever made a difference on the mileage except good versus diluted gasoline.

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2002 Liberty Limited 4WD, 3.7l V6
Steel Blue/Taupe
Selec-Trac, Offroad Group, Trailer Tow Group
1971 Dodge Challenger, 318cid, A904 Torqueflite


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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 4:45 am 
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Location: Hillsborough, NC / Corolla NC
take the tb off, remove the iac and tbps sensors and clean the tb real well, clean the iac or replace it if its too gunked up

x2 on going back to autolite or ngk's

if it has a loping idle when you start it up when it's warm, turn the key on wait for the dings to stop, mash the accel to the floor slowly, then let it back up, turn the key off then crank it normally and see if any of your issues dissipate

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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 1:58 pm 
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Location: IL
No loping idle. The only 'felt' problem is the stumbling at certain part throttle positions while decelerating. Literally, going along the road if I let off the gas just a little to start slowing down, I can feel and hear some stumbling/bucking. Let it off a lot, no problem.

New plugs and fuel filter, aye! Clean up the TB more than just a Sea Foam spraydown , aye! Check TPS, clean/replace IAC aye!

I'm replacing the muffler again soon too; the replacement is too loud; I have a better one (and a new 2.5" flanged lead-in pipe) to put in.

Worth considering the dealer controller reflashes?

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2002 Liberty Limited 4WD, 3.7l V6
Steel Blue/Taupe
Selec-Trac, Offroad Group, Trailer Tow Group
1971 Dodge Challenger, 318cid, A904 Torqueflite


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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 2:17 pm 
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With the correct plugs and fuel filter in place your stumble should go away unless there is something wrong with a sub system part like coils or injectors. Honestly if the stumble remains I woudl run pids on the ignition and injector cycles (and long and short term trims).

If the stumble goes away with the new plugs and filter then the only thing I could recommend for MPg improvements is make sure things like alignment, tire pressure and balance are within spec. The start making some mods. With a lift, bigger heavier meats and a surco rack (and renny light bar) Im still getting the same or sometimes better MPGs then I was with a bone stock renny. The mods I did improve performance and MPGs (although Im still stuck at 210hp 235 lbs/ft due to torque management).

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 Post subject: Re: Help me locate a driveability issue
PostPosted: Thu Jun 16, 2011 8:32 pm 
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Have you ever considered the Muffler may be your stumble? How long has it been there and what is it? When I was installing my Borla I took my jeep for a trip to the Beer Store with no exhaust, The lack of back pressure made it stumble when decelerating under load. To open of an exhaust can also rob power and Kill mileage.


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 Post subject: Re: Help me locate a driveability issue
PostPosted: Fri Jun 17, 2011 10:16 pm 
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Location: IL
The current muffler was installed about 18 months ago. It was supposed to be a 'moderate' performance muffler but it makes the Jeep sound like one of those nasty roller-skated sewer pipe hondas from a few years ago. I've just been too busy to get it replaced. The mileage didn't change at all when it replaced the factory muffler; just the noise.

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2002 Liberty Limited 4WD, 3.7l V6
Steel Blue/Taupe
Selec-Trac, Offroad Group, Trailer Tow Group
1971 Dodge Challenger, 318cid, A904 Torqueflite


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