Trying to improve mileage - what have I missed?
#1
Newbie
Thread Starter
Trying to improve mileage - what have I missed?
I am still working an improving mileage, and my '00 (82k miles) is still performing worse than my old '96.
Here are the mods / replacements I have done:1. Changed injectors to 12-hole
2. Changed all 4 O2 censors (NTK)
3. Changed TB to 62 mm
4. Changed air filter to KN
5. Changed TPS (Mopar)
6. Changed MAP censor (Mopar)
7. Changed spark plugs NGK, 0.4 gap
8. Changed spark plug cables
9. Viper Coil Mod.
10. Cleaned IAC
11. Changed oil
12. Changed thermostat from 180 to 195
13. Changed alternator + cables
14. Changed fuel filter
15. Changed temperature senders
16. Scorpion 1.7 roller rockers
What have I missed??? Anything else to check???
Here are the mods / replacements I have done:1. Changed injectors to 12-hole
2. Changed all 4 O2 censors (NTK)
3. Changed TB to 62 mm
4. Changed air filter to KN
5. Changed TPS (Mopar)
6. Changed MAP censor (Mopar)
7. Changed spark plugs NGK, 0.4 gap
8. Changed spark plug cables
9. Viper Coil Mod.
10. Cleaned IAC
11. Changed oil
12. Changed thermostat from 180 to 195
13. Changed alternator + cables
14. Changed fuel filter
15. Changed temperature senders
16. Scorpion 1.7 roller rockers
What have I missed??? Anything else to check???
Last edited by Morten Hjorth-Johansen; 02-22-2021 at 11:38 AM.
#2
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Join Date: Dec 2015
Location: PA
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Year: 1997
Model: Cherokee
Engine: 4.0L
Buy a Prius.
Just kidding. Id rather drive the XJ. What is the mileage like as is, and how much more are you after?
I dont see grounds on your list. They must be clean. Always. Also, whats the fuel pressure been like? And how is the coolant, being a 2000? Tire pressures?
Just kidding. Id rather drive the XJ. What is the mileage like as is, and how much more are you after?
I dont see grounds on your list. They must be clean. Always. Also, whats the fuel pressure been like? And how is the coolant, being a 2000? Tire pressures?
Last edited by fb97xj1; 02-22-2021 at 11:51 AM.
#4
CF Veteran
I've read that the injector "upgrade" doesn't really give you any better mileage... but rather more power... which = uses more gas, not save gas.
Maybe I'm wrong, but I've read that in a few places before.
Maybe I'm wrong, but I've read that in a few places before.
#6
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Join Date: May 2013
Location: Asheville, NC
Posts: 2,571
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Year: 1999
Engine: 4.0
There are so many other factors to mileage than engine performance. Tire size + gear ratio. Weight. Tire pressure. How you drive. We need more details. Also, how do you define "bad" mileage?
Also, why the 12-hole injectors and 1.7 roller rockers if you want to improve mileage?
Also, why the 12-hole injectors and 1.7 roller rockers if you want to improve mileage?
The following users liked this post:
ijeeep (02-23-2021)
#7
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Join Date: Oct 2019
Location: Current XJ is
Posts: 649
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Year: 95
Model: Cherokee (XJ)
Engine: 4.0
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#8
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Join Date: Oct 2019
Location: Current XJ is
Posts: 649
Received 174 Likes
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138 Posts
Year: 95
Model: Cherokee (XJ)
Engine: 4.0
I am still working an improving mileage, and my '00 (82k miles) is still performing worse than my old '96.
Here are the mods / replacements I have done:1. Changed injectors to 12-hole
2. Changed all 4 O2 censors (NTK)
3. Changed TB to 62 mm
4. Changed air filter to KN
5. Changed TPS (Mopar)
6. Changed MAP censor (Mopar)
7. Changed spark plugs NGK, 0.4 gap
8. Changed spark plug cables
9. Viper Coil Mod.
10. Cleaned IAC
11. Changed oil
12. Changed thermostat from 180 to 195
13. Changed alternator + cables
14. Changed fuel filter
15. Changed temperature senders
16. Scorpion 1.7 roller rockers
What have I missed??? Anything else to check???
Here are the mods / replacements I have done:1. Changed injectors to 12-hole
2. Changed all 4 O2 censors (NTK)
3. Changed TB to 62 mm
4. Changed air filter to KN
5. Changed TPS (Mopar)
6. Changed MAP censor (Mopar)
7. Changed spark plugs NGK, 0.4 gap
8. Changed spark plug cables
9. Viper Coil Mod.
10. Cleaned IAC
11. Changed oil
12. Changed thermostat from 180 to 195
13. Changed alternator + cables
14. Changed fuel filter
15. Changed temperature senders
16. Scorpion 1.7 roller rockers
What have I missed??? Anything else to check???
The following 2 users liked this post by ijeeep:
BlueRidgeMark (02-27-2021),
Morten Hjorth-Johansen (09-06-2023)
#9
Seasoned Member
The best way to restore the fuel efficiency of a 4.0L engine is to remove the head, clean the ports, resurface the valves and seats, and replace the springs. What really helps is bumping up compression. You can have the head resurfaced and then install it with a .030" head gasket from Cometic. That will get you over 9.3 : 1 compression.
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awg (02-27-2021)
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BlueRidgeMark (02-27-2021)
#11
Senior Member
Not meaning to be a smart a**, but the biggest detriment to gas mileage in a XJ is a headwind. I make some regular 250 mile trips in my XJ and my mileage varies from 17.5 to 22.0 mpg. Using the same speeds (cruise), same route, same fuel fill ups. The only variable was the headwinds.
Face it, we are driving a vehicle with the aerodynamics of a brick. Other then that, to increase fuel mileage you must increase the efficiency of your drivetrain. You can make it flow fuel better, but you had better increase the exhaust flow or it reflects negatively on your efforts. You can change the
gear ration of your axles, but it kills your low speed performance. It is all a trade off but still the headwind will be there or if you are lucky behind you! So my practice is just to maintain my stock drivetrain (change oil, tranny fluid, sparkplugs, etc) and hope for tail winds!
JMHO, YMMV
Face it, we are driving a vehicle with the aerodynamics of a brick. Other then that, to increase fuel mileage you must increase the efficiency of your drivetrain. You can make it flow fuel better, but you had better increase the exhaust flow or it reflects negatively on your efforts. You can change the
gear ration of your axles, but it kills your low speed performance. It is all a trade off but still the headwind will be there or if you are lucky behind you! So my practice is just to maintain my stock drivetrain (change oil, tranny fluid, sparkplugs, etc) and hope for tail winds!
JMHO, YMMV
The following users liked this post:
BillyBoy (02-24-2021)
#12
CF Veteran
The following 2 users liked this post by RocketMouse:
BlueRidgeMark (02-27-2021),
ijeeep (02-23-2021)
#13
Seasoned Member
I hate having to be that guy and I am not calling anyone out specifically. But some of you guys are really truly talk out of your *** lol. If you want better gas mileage you need to go with what has been tested to work. If anyone on here give you some gibberish about oh throwing magic pixy dust in my tank or removing my thermostat helped gain mileage don't listen to them, you'll be chasing your tail.
#14
CF Veteran
i.e..... 1999 XJ 4.0L, AW4, 110,XXX miles, (drivetrain stock), 235/75R/15 on stock rims, 2" lift
Typical driving - city & hwy averg speeds 30-70, most time around 45-50mph (are you getting into OD or not as well)
Driving style, relaxed (not agressive) no jackrabbit starts (not hypermiling, but not agressive)
Tire pressure, type of tires.
Alignment, do brakes drag?... etc... details of things that can affect the overall operation.
Current emissions if you live where they are required to be checked.
Fuel pressure at the rail, idle and under acceleration, temps , oil, coolant, etc. all can be factors too.
The more info like this you give all of us to work with the better we can help you with your question/issue.
I keep mine well maintained and I average 14-19mpg depending on the kind of traffic/roads I'm on through most of that tank of fuel. And I'm at sea-level.
Typical driving - city & hwy averg speeds 30-70, most time around 45-50mph (are you getting into OD or not as well)
Driving style, relaxed (not agressive) no jackrabbit starts (not hypermiling, but not agressive)
Tire pressure, type of tires.
Alignment, do brakes drag?... etc... details of things that can affect the overall operation.
Current emissions if you live where they are required to be checked.
Fuel pressure at the rail, idle and under acceleration, temps , oil, coolant, etc. all can be factors too.
The more info like this you give all of us to work with the better we can help you with your question/issue.
I keep mine well maintained and I average 14-19mpg depending on the kind of traffic/roads I'm on through most of that tank of fuel. And I'm at sea-level.
Last edited by RocketMouse; 02-23-2021 at 12:34 PM.