Gas Mileage

[justright92xj]

I happen to be a chrysler technician, so here is a TSB copied and pasted straight from Chrysler



NO: 18-12-92
SUBJECT: Long Crank Times And/Or Engine Die Immediately After Start Up
DATE: Jul. 27, 1992
THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 4.0 LITER ENGINE.

SYMPTOM/CONDITION:
Vehicle will exhibit long crank times and/or the engine will die out immediately after starting. This condition could be misdiagnosed as a fuel injector or fuel rail problem, but may be caused by a loss of fuel pressure at the sending unit supply hose.

DIAGNOSIS:
Verify that the vehicle has not been started for at least five minutes. Start the vehicle. Vehicles that have a long crank time or die-out immediately after starting should have the following procedure performed.
PARTS REQUIRED:
Quantity
Description
Part No.

1 Fuel Pump Outlet Hose Package
4713610
Consisting Of:

1 Fuel Outlet Hose
4713611

2 Clamps
4713612

1 0-Ring
53000575

1 Instruction Sheet
K6855030



REPAIR PROCEDURE:
This bulletin involves replacement of the fuel sending unit supply hose.

Remove the fuel pump module as outlined on page 14-4 of the 1991 Engine, Chassis, & Body Service Manual, Publication Number 81-370-1145.
Replace the original supply hose and clamps with the parts from package PN 4713610.
Using a new "O"-ring, install the original pump module as outlined on page 14-4 of the service manual.
Start the vehicle and inspect for fuel leaks.
Turn the vehicle off and allow it to sit for at least five minutes. Start the vehicle to verify that the condition has been corrected. If the vehicle continues to exhibit this condition, refer to page 14-36 (General Diagnosis) of the service manual.
POLICY:
Reimbursable within the provisions of the warranty.

TIME ALLOWANCE:
Fuel Pump Outlet Hose Replace

Labor Operation No.
Description
Time

14-50-90-90
MJ, XJ, YJ
1.2 Hrs


Optional Renegade Package Equipped

Labor Operation No.
Description
Time

14-50-01-63
YJ

0.5 Hrs.



FAILURE CODE:
Code Description: 59 Internal Leak

 

[MaXJohnson]

Huh? HOW MANY MPT?
Geez... I've got a 1991, and just finished a 4.5" lift. My 1st post-lift tank got me a whole 270 MPT, down from 310 MPT...

who's the brainiac that came up with this "miles per tankfull" crap? Is MPG that difficult to figure out :twak:

 

[hippymill]

This may seem like a silly question, but have you checked your catalytic converter If you are over 100000 miles, your cat might be plugged, and needs to be replaced. Poor mileage and reduced power are common symptoms.

 

[John(XJ)Jeep]

I think that most of the time it's due to a lead foot. Since your Jeep drives like a house you might tend to hit the throttle harder and keep it down to accelerate normal like it did before all the mods. Your just gonna have to be slower driving down the road if you don't want to burn up gas. If you want to accelerate, say like going on the highway just do it slowly and don't make sharp jabs at the throttle.. doing that wastes a lot of gas. So basically drive like a granny and see if you mileage changes. If it changes a lot then obviously you know what's wrong.

 

[shawnmahmud]

My to-do list for a '98 XJ getting about 12mpg (down from 17mpg a year ago):

- new catalytic converter (original, sometimes smells like sulfur which I've heard means moisture inside)
- new #1 Oxygen sensor
- fuel system cleaner
- change rear diff (chrysler 8.25") fluid and refill with 75-140W synthetic (live in MN and local dealer says it improves mileage in low temps)
- clean out CCV tubing b/c I have oil residue coming out the valve cover at the attachment that runs into the air filter box


Suggest additions/deletions?...my budget for this can't go much past $250 right now. Cap/rotor/plugs/wires replaced 2 years ago (~40,000 miles).

Thanks-

 

[icebreaker88]

I am in the same boat with my 93 4.0
I was told it was rebuilt about 40k ago, no cat high flow muffler.
I have only had the jeep for 2 weeks now and it is useing fuel bad.
It has 32" tires and I think stock gears, I got only about 150mile out of a tank full of about 18 gallons. Not sure about the speedo being of, if it is it is not by much. I am going to check it soon with my GPS.
Also I have a hard starting problem, that I have to hold down the pedal to get it to startmost of the time, Does not matter if it is hot or cold. It idles fine after it starts. And no check engine light on.
This is my first jeep,
Thanks for any help

 

[John(XJ)Jeep]

Are you carburated??? A 93' 4.0L you say, Heheh I thought they didn't make those anymore before that. Well if you not carburated; fuel injected, you shouldn't have to put your foot on the gas at all to start. Sounds to me your fuel is being plugged somewhere. Fuel filter? Fuel Pump? Plugged injectors, you got to check all that. Sometimes a sensor can even make it hard start.

Like I said before, try driving like a granny. If your mileage improves then you know what the problem is. It's your foot.

 

[87manche]

All 4.0's are fuel injected, renix from 87-90, OBD-1 from 91-96(?), obd-II 97+
Sounds to me like the motor is choked until you put your foot on the throttle.
I'd do a through cleaning of the throttle body and intake first. Make sure the butterfly is seating properly. Clean the IAC bore and the Pintle. If it's stuck shut then it's not getting enough air at startup. Verify that the TPS is sending the proper voltages and doesn't have a dead spot, you can do this with a DMM. Search TPS Adjustment, you'll find more info than you ever wanted.
As for the fuel mileage, 32's and stock gears would probably do that. With 32's I think most people around here would recommend 4.56's or maybe even 4.88s

 

[John(XJ)Jeep]

Well there you go.

 

[vertigospiral88]

I thought OBII was a requirement for the '96 model year (fed mandated)? Could well be wrong, but seems like most manufacturers changed in '96.

All 4.0's are fuel injected, renix from 87-90, OBD-1 from 91-96(?), obd-II 97+
Sounds to me like the motor is choked until you put your foot on the throttle.
I'd do a through cleaning of the throttle body and intake first. Make sure the butterfly is seating properly. Clean the IAC bore and the Pintle. If it's stuck shut then it's not getting enough air at startup. Verify that the TPS is sending the proper voltages and doesn't have a dead spot, you can do this with a DMM. Search TPS Adjustment, you'll find more info than you ever wanted.
As for the fuel mileage, 32's and stock gears would probably do that. With 32's I think most people around here would recommend 4.56's or maybe even 4.88s

 

[wrstlr119]

The hard starting problem could very well be the fuel pump. When I first go my jeep it got harder and harder to start until a shop replaced the fuel pump. Starts great now. As for the mileage, my 98 with stock gears and 31's only gets around 14. I've got a new speedo gear and rusty's intake/exhaust.

 

[Rapoza]

I also have mileage problems in my 4.0XJ and I get around 11mpg. Also my car stands too much to start. The heads new and all shiny around. I had the same mileage with the old cracked head and before the rebuild. Headers are repair welded.
Seems to me that there are too many of us getting that same mileage of around 250 miles with a full tank versus others do 400+. I think theres something we're omitting in test or knowledge of our jeeps.
As for the type of gas... I have same problem overseas no matter its Repsol, Shell...

I'm sure it would be good if we also state the type of transmission we have and if auto, the rev range it works while starting from the light, as a way to know the healt of it.
Perhaps the mileage problem has more to do with sliping autos than sensors, don't u agree?

I have an auto and it always wants to move 2000+ revs when 1st or 2nd.
Also have a crap for muffler and heat pipe.

 

[87manche]

OBD-II might have been in 96, that's why I had a question mark.
I just got back from WF, and on the highway, doing 75 my MJ averaged 23.5 MPG
I have a 5sp, 3.07s and 31's. Cruising RPM @75 is 2250

 

[clean96XJ]

I have a 96 4.0, manual, K&N filter, 30's All-Terrain tires, no lift, 3.07 gears and only 71k on it. I average 16 mpg with mixed driving. My foot is a little heavy but, it stills seems low when you start considering 2,250 rpm @ 75 and don't carry any extra weight.

400 miles per tank is crazy. no way.. but 300 (for 18 gals) should be obtainable.

orig specs for 96 Cherokee 5 speed 17 city 22 highway 19 mixed.
http://www.fueleconomy.gov/feg/noframes/13204.shtml

Definitely, consider type of tires well comparing mpg because aggressive treads will lower mileage.

 

[highhilleer]

I have a 96 4.0, manual, K&N filter, 30's All-Terrain tires, no lift, 3.07 gears and only 71k on it. I average 16 mpg with mixed driving. My foot is a little heavy but, it stills seems low when you start considering 2,250 rpm @ 75 and don't carry any extra weight.

400 miles per tank is crazy. no way.. but 300 (for 18 gals) should be obtainable.

orig specs for 96 Cherokee 5 speed 17 city 22 highway 19 mixed.
http://www.fueleconomy.gov/feg/noframes/13204.shtml

Definitely, consider type of tires well comparing mpg because aggressive treads will lower mileage.

I just analyzed my fuel consumption for a year and I get the 22 on the highway, but lower in city driving (must be all the hills). Overall average is 17 mpg. 97 - 4.0 automatic, totally stock

 

[Rapoza]

400 miles per tank is crazy. no way.. but 300 (for 18 gals) should be obtainable.

Sorry Clean, I was so sleepy that day.
I just received the new TPS and IAT and will be replacing it in a while, together with crancshaft seals to get ride of my oil leak.

It could be interesting if anyone popular here make a poll with the bad/good mpg and the tranny type in question. I guess bad mpg is propiciated by an auto (a trouble with)

Geetings,

 

[Cjmartz2k]

4.0 automatic, totally stock

What is this "stock" that you speak of and where do I buy it??

 

[pikey77]

01 4.0 auto with 30" Tires I average 20.2 per gallon. Cruise control set on 65 and average acceleration. I've gotten 22MPG by keeping acceleration revs below 2,000. Best I ever got was 29 on the way from Albuquerque to Dallas...I thought my bladder was gonna explode. I get about 317 tell the low fuel light comes on when I top from there its generally 16.5 gallons. So with 20 gallons 400 miles is stretchin it but doable.

 

[T&A-XJ]

Dont know how it relates to your XJs and your economy but throughout the years the torque peak RPM changed several times. I dont know all the values but mine I believe is at about 2400RPM(1990) and my cruising RPM is just shy of that at 70MPH. From what Ive always heard is that an engine runs most efficient at its TQ peak RPM. With all the armor, lift, tires, gear, spares ect I get 17MPG average. On flat freeway trips with minimal gear I can get 20MPG. On the way to Moab last year I got 18-19MPG with a consistant average speed of 80+MPH and a scale weight of well over 5k(full family and all the crap that goes with them). My wifes XJ is a 94 and her cruising RPMs are 200RPM or so lower and we're lucky to get 17MPG all freeway miles. In the 94 I believe the TQ peak went up to 3500RPM or something, havent looked in a long while. That being said I cant imagine her XJ getting better mileage in 3rd gear at 70 but maybe a cam change would change everything?

Another thing I noticed a change was when my alignment was off considerably. The toe in was way off and ball joints bad as well. After the alignment it was noticeably smoother rolling and did help economy quite a bit.

Just a thought, whether it is worth anything or not Im not sure...


BTW my XJ Limited has 5.5" 33" 4.56s auto and several light engine add ons like exhaust, intake. Hers is a Sport, 4" 31" 3.55s auto but alot less weight.

 

[krakhedd]

I don't have time/focus to read through this whole thing, but you have a similar setup to what I have on my '01, so a couple of quick observations.Opening up the exhaust reduces low-end torque, which also reduces efficiency at lower engine speeds due to too little backpressure. I think this is where my efficiency went shot, and probably where yours went also. (I get similar mileage)I have not found a solution to my problems yet, nor do I anticipate finding one any time soon. I have no money to sink into R&D on the subject, preferring to send it all to Iran and the Middle East via my gasoline purchases.Replacing an O2 sensor will do nothing unless the sensor is high mileage (they usually go at 75k-100k).