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Unread 04-13-2003, 03:09 PM   #1
Rockhound79
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Poor gas mileage

New owner of a 1998 Jeep Grand Cherokee Laredo TSI. Gas mileage is about 11.5 hwy at best. Sent it back to the dealership for servicing. They ran some computer diagnostics and reset the car's computers, but to no effect. I have topped off the tires and changed the air filter, also not much help. If this is a known problem or anyone can lend helpful advice, I would greatly appreciate it.

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Unread 04-13-2003, 05:57 PM   #2
Ryan2son
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When I purchased my Jeep last November I performed as much scheduled and preventative maintenance that I could do on my own. This included:

Mobil 1 5w30 full Synthetic oil w/mobil 1 filter
air filter
BG gas treatment (the best on the market!)
Complete drivetrain fliud change
Radiator flush
Champin spark plugs (recommended by Jeep)
- note: I don't believe my pluges were EVER changed (the best one had a .65 gap!) and this could be one of your problems. Jeep told me that you need to use the prescribed plug or it could mess up the computer. Maybe!?!?

In short since you already changed your air filter I would change your plugs and run BG gas treatment. Once you do that then fill up the tank with good gasoline, drive it (no lead foot) and get back with us.

I get ~16mpg in the city and ~21mpg on the highway.

Questions: How many miles are on your ride? Other than gas mileage does it run well?
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Unread 04-13-2003, 05:58 PM   #3
Texas ZJ1
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What type are you looking for?

What are your driving habits?

When was the last time you did a combustion chamber or "carb" cleaning?

Do you have stock tires?

Do you have a high performance intake?

What gearing do you have?

I'm asking all these questions to figure out how and maybe why your mileage isn't what you want.

I get about 11 to 12 city and 17 to 18 highway.

Hunter
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Unread 04-13-2003, 06:41 PM   #4
Rockhound79
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Thanks for the speedy reply fellas. I'm not overly automotively inclined plus I've had this Jeep for a little over two weeks now, I just figured solve this issue now while the dealership still remembers me. I'm pretty light on the pedal. The car rides very well with about 55K mi. (on a side note, shuddered and stalled at 65 m.p.h. week ago on 95. let it sit and was alright. have since added dry gas) anyway, im not sure what my gearing is, my intake is factory. didnt look hard at the tires yet, but they're not anything close to heavy off road diggers. i have been told too that i can get the fuel system cleaned w/ pressurized air. i've been to the EPA's website and this model is supposed to be 15 city/ 21 hwy. anything within 1-2 mpg of that is acceptable, but for a grand cherokee to be getting worse mileage than an H2 is crazy. your mileage isnt that bad Texas, i could live with that. I'll get back to you guys soon after i try some new plugs and get the injectors and such cleaned. thanks again.
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Unread 04-14-2003, 12:41 PM   #5
automan25
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What formula are you using to determine your mileage? If you are using the computer in the Jeep, then don't...it's not accurate, at least mine isn't. You'll have to calculate it out on paper. I get about 12cty/17hwy with the 5.2 litre engine. Those figures are based on several months of driving records.
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Unread 04-14-2003, 07:18 PM   #6
brad335
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welcome to the world of driving a jeep. They dont get good gas milage. But get a K&N filter...you wont regret it
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Unread 04-15-2003, 12:16 AM   #7
g0Nzo
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if it shuttered and stalled there could be a timing proble im not fermiliar with the timing drive type on your model but i know that the last mopar i had was gear to gear and it would do the same thing it turned out to be the timing. You could try a new distributor, and rotor. Replace the plug wires and plugs, gaps should be like .33-.35. And for godsakes no dry gas especially not with fuel injection. Use some STP fuel treatment 1 whole bottle for a full tank of gas get those injectors cleaned out.
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Unread 04-15-2003, 02:40 PM   #8
Rockhound79
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I've been computing mileage on paper, i know the on board digital readout is unreliable. its been a bit better than before up a mile or two per gal, probably the new air filter and tire pressures. im going to replace the plugs too. I might give that BG a whirl too, although its been my experience that most of these fuel additives are just a waste of money. how about that K&N filter too? they're bout $60 by me, do they take much maintenance? whats they're life expectancy?
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Unread 04-15-2003, 05:07 PM   #9
automan25
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I have a K&N on my 69 Mustang. I only have to clean it about once a year, and it's supposed to last through 20 cleanings. 60 bucks for 20 years of service isn't a bad investment
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Unread 04-15-2003, 06:58 PM   #10
kbohip
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Quote:
Originally posted by Rockhound79
I've been computing mileage on paper, i know the on board digital readout is unreliable. its been a bit better than before up a mile or two per gal, probably the new air filter and tire pressures. im going to replace the plugs too. I might give that BG a whirl too, although its been my experience that most of these fuel additives are just a waste of money. how about that K&N filter too? they're bout $60 by me, do they take much maintenance? whats they're life expectancy?
A good fuel additive like BG or even Techron is not a waste of money. I've used them before on used cars I've just bought, and the results have been great.
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Unread 04-17-2003, 02:23 PM   #11
Intrepidjeep
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I tend to not use the fuel system cleaners. You can't possibly know whether your fuel system needs any sort of cleaning without getting it diagnosed. And the aftermarket fuel system cleaner advertisers sure want you to use their product regularly to keep your fuel system clean.

However, a bottle of cleaner isn't a very expensive gamble if you seem to have a problem with the vehicle.

Consumer Reports has said, in their reviews of different brands of gasolines, that if you use a decent brand name of gasoline that has good detergent additives (I recall them mentioning Chevron as well as Amoco, Texaco, Shell and one or two others), then aftermarket fuel system cleaners are usually not worth the money.
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Unread 04-17-2003, 06:42 PM   #12
ILoveto4x4inNC
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Jeep says only use Champion plugs? I'm running Bosch Platinums in my 5.2 and haven't had any trouble with the computer. Did help my milage, however I think it's about time to do it again. 30K miles/year in stop and go traffic is hard on plugs among other things. Been noticing the milage going back down on me, still in the 15s but it can do better. My computer shows the same as when I calculate out myself.
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Unread 04-19-2003, 04:38 PM   #13
Rockhound79
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Have yet to replace plugs, plus i need that special pliers to pull the boot off. but i did get an updated mileage computation of a tiny bit over 11 mpg for last week. filled on monday morning and by friday evening had gone through 3/4 tank. that includes about 2 hours of idling also so possibly a bit better, but not much. ive got a trusted mechanic who i might ask to check it out also. someone told me about a charcoal filter canister? has anyone heard of this component and is it linked to mileage in any way. i think its something for fuel vapors but i could be wrong.
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Unread 04-19-2003, 04:58 PM   #14
Intrepidjeep
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Yes the canister stores vuel vapors rising out of the gas tank -- the computer theoretically does a quick purge of the canister (I think it waits until a certain engine temp is reached), sucking the vapors into the intake.

I suppose if the canister solenoid were stuck so that you were constantly drawing air all the time through it, but I don't know how that would really affect gas mileage. Seems the computer would compensate, and you'd probably get a check engine light on the dash as well. Not sure.
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Unread 04-20-2003, 01:48 PM   #15
Stocker
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About that K&N...

Shop around, I can't remember what I paid but it was a lot less than $60... I'm thinking maybe half that. But that's the replacement panel, not the cone. Get a service kit too; it has cleaner and oil.
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