Could it be that your son has a very heavy foot on the skinny pedal? In the 70's, I did! Swore I didn't.

 

HAHA, I thought of that until my wife drove it for a few days. I verified the mileage by doing the math (no computer). Just looking for some input.

 

Is the driving mainly in stop and go traffic or highway cruising? Do you live in a cold climate? I've only gone through 1 tank so far on my "new to me" 2002 4.7L WJ after changing the spark plugs and only got 12mpg (pen and paper calculated). That was after changing out the plugs and making sure the new ones were gapped correctly to 40thou.
For me, I'm chalking my 12mpg to the following possibilities (I hope so at least):
1. lots of stop and go traffic on my daily drive to work and back
2. Winter gas
3. cold weather. More dense air =more fuel needed for the ecu to meet an air-to-fuel ratio target (not sure if the ECU has compensation tables or how much an effect this has. Also depends on engine load)

I had a 2002 4.7L WJ five years ago and I remember getting at least 15-17mpg average in summertime with a bit of a heavy foot.

 

I have the 4.7L H.O engine and 12 mpg is all I've ever gotten in city driving. I figure the engine just guzzles gas. But I don't do massive mileage in it so I can live with it.

 

I drive fairly conservative around town and get about 12-13 mpg, it's a fairly heavy vehicle and does guzzle gas. I've found that reasonable acceleration from a stop saves a lot of gas compared to just getting up to speed fast.

 

Do you know the condition of fuel and air filter? Might be worth changing out if previous owner isn't sure. For the record, 2004 4.7L around town 14.7. Highway jumps up but no long term data yet for me.

 

Edit to post #7: Should have read "combined" not around town. Not permitted to edit my posts yet.

 

Thanks for the heads up team. Sounds like we're all in a similar boat with fuel mileage. I just remember it being better when we first bought it but the weather was nice at that point. now its cold as ballz where I live. Just wondering if anyone else out there has changed any speed sensors and had any success?

 

In the summer, I'd get about 17 mpg on the highway and 14 mpg city. With the cold weather I'm down to 11 mpg city. Haven't done any highway miles yet.

 

My 04 was knocking down about 13-14 mpg city when warm, now that it is cold 12-13 city. Got up to 17 once during a highway trip, however it was a bit cold then also. New plugs, air filter, injector cleaner ran through it. I did notice the weight of my foot has a huge effect on mileage. It isn't really out of line for the type of vehicle and when one considers what the older 4x4's got it is downright great. I have had many 4x4's in the past from Suburbans to K5 Blazers and pickups and none of those had close to the performance of my WJ and not near the mileage. With hubs disconnected cruising 55 the best any of the old ones got was maybe 12 on the highway.

 

/me shakes fist at winter gas

 

be sure to use correct plugs!!!
As for the coils.... I would hold offf spending right now.
At the part stor have the system SCANNED even if CEL is off !!! important.

You mention a TPS, a SRS light - gotta ask does the cruise control work? Any horn issue?

 

I have a 2001 wj laredo with the 4.0L i6 and im getting 9 mpg lmao. I dont even think my average has ever even made it to 10. big jeeps need big gas.

 

I had an injector short out, causing the harness to melt. Once the harness melted, it caused a ground on the injector keeping it open all the time. Mileage went to **** .

 

Check the vac hoses near the intake for cracks. If they are letting in un-metered air, the O2 sensors will see it and start adding fuel to richen the mix. Maybe not enough to throw a code but enough to make mileage go to h3ll. Mine were in terrible shape. Also consider swapping o2 sensors as they can get lazy with fuel trims.

Other stuff mentioned is good too. But as noted, leave the coils as is. They do not often go bad and are expensive. They either work or do not. Plugs, fuel filter and then remove/clean the throttle body. Clean the IAC valve and the barrel of the TB. The IAC is also normally a work or not work item too. So much in the way of improvements there. It can develop "dead spots" in the voltage sweep but that's about it and it normally throws a code when it heads south.

 

My combined average for hiway, town and off road is 16.7. Off road mileage, hand calculated, runs 10-11 mpg and that's a lot of low range driving, hill climbing etc. On the hiway I get 22-24 mpg. I am running 32 x 10.50 tires which also affects the mileage. I used my SuperChips tuner to change the tire size so the shift points are restored and the spedo is accurate. Also changed the tune to the SuperChips 87 octane one. Power and shifting are both great and so is the down hill holdback in low range first gear. Car has 82,xxx miles on it and I'm thinking of changing the plugs.

 

I’ve improved my 2000 wj 4.7 milage over the past several months. This is what I did to improve it: stopping vacuum leaks, new plugs, and coils. I was getting less than 10 and now I’m getting between 13-14 city....winter time driving. I highly recommend new ignition coils. As a suggestion a good shop can hook up a real time diagnostic computer to check all vitals and sensors. Numerous other sensors can effect milage: O2, MAP, Fuel/air ratio.

 

1999 WJ 14 in town. 19 - 21 hwy.

2005 WK 12 in town. 18 hwy.

Both are 4.7L...

 

dirty injectors will cause this replace plugs and clean or replace injectors

 

Try checking your brake calipers.

Two times , my gas mileage started to go down. Each time, one of my brake calipers went bad. Driving with your brakes on is bad for your mpg.

 

I have 04 WJ 4.7L V8. In the summer time, a full tank of gas would get me 300-320 miles. Now I am only getting 250 or so miles on a full tank because its winter and I have been really having fun with it during my commutes (read: I have a lead foot).

I usually try and keep it below 2k rpms for best mpg. Even when accelerating, dont push it above 2k and that will really help.

 

15 year average mileage

We had a 2002 4.7 GC and a 2002 4.7HO Overland. After keeping a record of every fillup for 100,000+ miles on both until they were sold in 2016 and 2017, the mileage was consistently 13-14 in town and 18 +or- on the road.

 

^^ That is some great info there. That is right on par with what I see with my 04 4.7 Limited.