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Fuel Economy Problem

X

X9x A T I x7X

NAXJA Forum User
Location
Pennsylvania, New York, Delaware
My '94 XJ is only getting 8mpg city and 11.2 highway. A friend of mine works for Absolute Performance and let me put it on the dyno yesterday. I found out I have 196hp and that gas milage. I thought this was really low, so I searched through the threads here on gas milage and indeed it is. Can anybody tell me what might be wrong with it?

.......No wonder why I'm too broke to afford any upgrades on it. Geez... I have $7 to my name :banghead:

1994 Jeep Cherokee Sport 4.0L HO I6

I am also idling extremely low (300 range), could this give a clue to what's up? Don't the 4.0" I6's usually idle at about 800?
 
Last edited:
Where to start?

Plugs, wires, cap & rotor.

Injectors & seals.

Air filter.

Cracked exhaust manifold.

O2 sensor.

Coolant Temp Sensor (not sender).

Thermostat.

Big tires.

Underinflated tires.

Lead foot.

Bad alternator.

And others.
 
joe_peters said:
Where to start?

Plugs, wires, cap & rotor. <-- Done this past summer

Injectors & seals. <-- Done in august

Air filter. <-- Done a few weeks ago

Cracked exhaust manifold. <-- Done this past summer (Found a great deal on eBay too!!)

O2 sensor. <-- H2?

Coolant Temp Sensor (not sender). <--H2?

Thermostat. <-- Done this summer

Big tires. <-- 29"x7" = Not big lol

Underinflated tires. <-- Sitting at 50 psi

Lead foot. <-- How I drive doesnt really seem to effect it. I've played around with my driving and it hasn't made any change worth driving the speed limit. I'll just keep up with other drivers around here; we all know where the gas pedal is. :laugh:

Bad alternator. <-- Just replaced a few weeks ago

And others.
Click to expand...
 
Are you positive that it is still 4.0 and not stroked to 4.6.? That might account for the MPG. 4.0 stock is 190hp at crank, much less at wheel. Never heard of a motor picking up about 20-25% HP after 15 years of use.
 
Sounds like there isn't much else that you haven't already done.

My 90xj 2-dr is getting 15.7mpg on my last 200+ mile trip, mostly hwy but a lot of hills.

I have Bosch Platinum + four plugs, cheapo cap/rotor/wires, K&N 6" cone filter w/Rusty's intake tube, Ford (Bosch) orange top 19 lb injectors, 31x10.50x15 tires at 40 psi, 4.5 front/5.5 rear lift, 195 degree thermostat with all sensors functioning, no exhaust or intake leaks, running 10w30 Chevron motor oil, 10w30 Mobile-1 in AX15, alternator is old but no bearing noise, and I tend to romp on it 1st/2nd gears.
 
93gc40 said:
Are you positive that it is still 4.0 and not stroked to 4.6.? That might account for the MPG. 4.0 stock is 190hp at crank, much less at wheel. Never heard of a motor picking up about 20-25% HP after 15 years of use.
Click to expand...

It's definitely not stroked. Wish it was, but I seriously don't have the money for that. This vehicle had two owners before me, a woman who drove it like a grandma and hit everything in sight, and my sister who took it mug bogging at 70mph and hit everything in sight. Mainly things that didn't move, like trees, and poles, a house, and yes, a 500' iron bridge. 3 TIMES!!!

My parents bought the Jeep for me last year and told me if I could fix it, it was mine. After replacing the plugs, wires, dist, alternator, battery, intake manifold, exhaust manifold, front exhaust pipe, catalytic (Cheap junker that's already hollowed itself out), muffler, tailpipe, tires, 2 rims straightened, windshield, all wipers, rear wiper assembly, both headlights, rear brakes (drums and pads), all speakers, head unit (Didn't have one), intake box and filter, oil change (The ONLY time i've ever seen chunky oil come out of an engine, much less one that runs), fuel filter, steering wheel (some :smsoap: stole it!!! Who steals a stock jeep steering wheel?!?!?), starter, and a trans pan and seal........... I am now convinced I've spent more fixing it then the vehicle is worth itself. After washing it for the first time, I found out it is actually green, and not brown!! That was a shocker lol. This thing has been through hell, and as a firefighter, I have much more to throw at it. I have a straight official access road that I take to my station when we get calls that I usually top the Jeep out on, depending on the weather. Atleast it will have some regular maintenance though. :)
 
I have no idea with this machine. Even my dad was impressed with the power it has, being that it can compete with their '08 Envoy which puts out 285 to the wheels. It's got some beef too it, but maybe thats just its way of dealing with its past drivers =D I'd be pretty Po'ed too lol. I can't wait until I can upgrade to a heavy duty driveshaft and burn these tires off. Every time I do it now I shred the driveshaft for some reason. It has, as far as i'm concerned, close to the stock torque for these machines, but something isn't right.
 
Know anything about what is in the rear differential?

Is it lifted? Read somewhere a guy had his front end higher than the rear, when he lowered the front to a little less than the rear his mileage improved--wind resistance!

By the way--that is one lucky XJ, you better hold on to it! LOL!
 
Well I have no Idea what to say.. I get 12-17 mixed driving. Mostly dependent on the amount of HWY time and how heavy I am on the skinny peddle. Most of your problem might just be the right foot usage.
 
ok here's what you do. go to a shop and have them use a scan tool while the jeep is running, dont check for codes, you want to see what the computer is telling the OBDII, for example, it will tell you if your running rich (which you prob are) or lean, spark adv. timing, etc. etc. i use a snap-on scan tool for this, but its preeeettyyyyy expensive which i why i say take it to a shop. Have them give you a print out of the findings.
 
joe_peters said:
Know anything about what is in the rear differential?

Is it lifted? Read somewhere a guy had his front end higher than the rear, when he lowered the front to a little less than the rear his mileage improved--wind resistance!

By the way--that is one lucky XJ, you better hold on to it! LOL!
Click to expand...

Umm, no, I believe it's actually lower because of the severe abuse the suspension has taken. Suspension systems can only take so many 4-7' drops before they quit. The front end is higher then the rear however, not only how the body sits, it is actually physically higher.
 
93gc40 said:
Well I have no Idea what to say.. I get 12-17 mixed driving. Mostly dependent on the amount of HWY time and how heavy I am on the skinny peddle. Most of your problem might just be the right foot usage.
Click to expand...

As stated before, my driving didn't really effect the mpg when I was messing around with it. I'm not hard on the throttle pulling out, but my average highway speed is around 80-85, which is the average around here.
 
Jeepcherokeeboy97 said:
ok here's what you do. go to a shop and have them use a scan tool while the jeep is running, dont check for codes, you want to see what the computer is telling the OBDII, for example, it will tell you if your running rich (which you prob are) or lean, spark adv. timing, etc. etc. i use a snap-on scan tool for this, but its preeeettyyyyy expensive which i why i say take it to a shop. Have them give you a print out of the findings.
Click to expand...

When I get some money I will try that. I am currently unemployed, as is 3/4 of the population around here. The economy pretty much killed this town. :bawl:
 
You could put some lift shackles on the rear to try and get a nose-down attitude.

Also, in that JP Magazine article they were getting 6.8 mpg until they changed the O2 sensor--jumped to a solid 16 mpg. That is a major difference in anybody's book.
 
Test first, easy fix if bad--just costs money to replace.

Test it.
 
it would replace the O2 sensor as stated above. Cheapest and most logical part to replace especially if it has never been changed. and it is super easy to change. Disconnect neg battery teminal. disconect connector at O2 (on the Ehaust pipe incxase your not sure) screw the oldy out and put that new SOB in. Connect neg bat cable and your good to go! as long as the batt is disconnected you shouldnt have to worry about it throwing a code. good luck and keep us posted with the results!
 
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