Mudderoy
04-26-2010, 02:38 PM
I have been fighting my gas mileage ever since I lifted my 1998 Jeep Cherokee about 3 years ago.
I really didn't take notice of the gas mileage prior. Either it was about the same that I had been getting for the prior 9 years or the $1.50 to $1.80 a gallon cost I just didn't care.
I fully expected my mpg to go down due to the larger tires. It wasn't until I started reading of mpg claims on NAXJA of 17, 18 miles per gallon with simular lifts and tire sizes, that I decided I was a fool for excepting my 10+ miles per gallon.
I started with a tune up. Plugs, rotor, cap. Then the O2 sensors. I had the gears changed to 4.56 (I had larger tires plans for the future). I replaced the cracked exhaust manifold with a header. I replaced the OEM muffler and catalytic converter with a flowmaster. I replaced the plug wires. Recently I replaced the coil. I replaced the CPS. I replaced the fuel injectors. I bought an OBD II elm327 scanner that allows you to hook up your ECM to a laptop and record real time data. I've replaced the wheel bearing assemblies.
This told me I was running rich!
I cleaned the throttle body. I replaced the TPS. I replaced the IAT sensor.
Over time my mpg has increased from high 10's to a high of 13.7 mpg. I found that having the NP242 in full time 4x4 cost me about 1.5 mpg.
The most recent change were the fuel injectors. I have yet to determine if this made a positive difference yet. I should have a better idea in the next few days.
I have NOT increase the amount of air coming into the intake. K&N for example. I like the idea of this, I don't like the cost, but mainly I don't like the idea of having something like that on a 4x4 that might possibility find myself in deep water. I think the factory box affords more protection against high water than the K&N would. I do have future plans for a snorkel.
I have improved the exhaust flow, and increased the fuel atomization in the cylinder. Initial readings from the OBD II scanner show that my O2 sensor is now producing a saw tooth pattern over a much wider range, and if I understand correctly this means I am no longer running rich. I am running normal.
I recently (re-read) this article (http://www.4wheeloffroad.com/features/131_0402_jeep_xj_mileage_upgrades/index.html) on 4wheeloffroad.com. They took a 1993 Jeep Cherokee and made several modifications to improve the fuel economy. They are running 33" tires with 3.55 gears.
They increased air flow, exhaust flow and then added a Performance Distributors FireWire kit.
Based on this article and their results I decided to spend the nearly $200 for a rotor, a cap, plug wires and a coil!
I checked with several xjtalk vendors (as you should ALWAYS do) and several of them carry, or can get the Performance Distributor Firepower Ignition Kit - 4.0 Liter 6 Cylinder (4.0KIT). They do make a kit for the 2.5 as well.
Ultimately I went with Jeepin' Outfitters (http://www.jeepinoutfitters.com/scripts/default.asp). xjtalk member and vendor!
You can purchase this kit by going to this :link: (http://www.jeepinoutfitters.com/scripts/prodView.asp?idproduct=2169)
http://www.performancedistributors.com/4.0kit.jpg
You can select black, blue, or red. I selected RED! :rotfl2:
I received a PM today from Jeepin' Outfitters because they noticed my XJ is a 1998. It seems the OEM cable connection to the coil changed in 1998 and 1999. This requires an adapter!
http://www.performancedistributors.com/31728-ah.jpg
This is an additional $30(ish). You could always get an earlier model plug from the junk yard and re-wire the connector if you wanted to.
(more to come, including hopeful mpg gains!)
I really didn't take notice of the gas mileage prior. Either it was about the same that I had been getting for the prior 9 years or the $1.50 to $1.80 a gallon cost I just didn't care.
I fully expected my mpg to go down due to the larger tires. It wasn't until I started reading of mpg claims on NAXJA of 17, 18 miles per gallon with simular lifts and tire sizes, that I decided I was a fool for excepting my 10+ miles per gallon.
I started with a tune up. Plugs, rotor, cap. Then the O2 sensors. I had the gears changed to 4.56 (I had larger tires plans for the future). I replaced the cracked exhaust manifold with a header. I replaced the OEM muffler and catalytic converter with a flowmaster. I replaced the plug wires. Recently I replaced the coil. I replaced the CPS. I replaced the fuel injectors. I bought an OBD II elm327 scanner that allows you to hook up your ECM to a laptop and record real time data. I've replaced the wheel bearing assemblies.
This told me I was running rich!
I cleaned the throttle body. I replaced the TPS. I replaced the IAT sensor.
Over time my mpg has increased from high 10's to a high of 13.7 mpg. I found that having the NP242 in full time 4x4 cost me about 1.5 mpg.
The most recent change were the fuel injectors. I have yet to determine if this made a positive difference yet. I should have a better idea in the next few days.
I have NOT increase the amount of air coming into the intake. K&N for example. I like the idea of this, I don't like the cost, but mainly I don't like the idea of having something like that on a 4x4 that might possibility find myself in deep water. I think the factory box affords more protection against high water than the K&N would. I do have future plans for a snorkel.
I have improved the exhaust flow, and increased the fuel atomization in the cylinder. Initial readings from the OBD II scanner show that my O2 sensor is now producing a saw tooth pattern over a much wider range, and if I understand correctly this means I am no longer running rich. I am running normal.
I recently (re-read) this article (http://www.4wheeloffroad.com/features/131_0402_jeep_xj_mileage_upgrades/index.html) on 4wheeloffroad.com. They took a 1993 Jeep Cherokee and made several modifications to improve the fuel economy. They are running 33" tires with 3.55 gears.
They increased air flow, exhaust flow and then added a Performance Distributors FireWire kit.
Based on this article and their results I decided to spend the nearly $200 for a rotor, a cap, plug wires and a coil!
I checked with several xjtalk vendors (as you should ALWAYS do) and several of them carry, or can get the Performance Distributor Firepower Ignition Kit - 4.0 Liter 6 Cylinder (4.0KIT). They do make a kit for the 2.5 as well.
Ultimately I went with Jeepin' Outfitters (http://www.jeepinoutfitters.com/scripts/default.asp). xjtalk member and vendor!
You can purchase this kit by going to this :link: (http://www.jeepinoutfitters.com/scripts/prodView.asp?idproduct=2169)
http://www.performancedistributors.com/4.0kit.jpg
You can select black, blue, or red. I selected RED! :rotfl2:
I received a PM today from Jeepin' Outfitters because they noticed my XJ is a 1998. It seems the OEM cable connection to the coil changed in 1998 and 1999. This requires an adapter!
http://www.performancedistributors.com/31728-ah.jpg
This is an additional $30(ish). You could always get an earlier model plug from the junk yard and re-wire the connector if you wanted to.
(more to come, including hopeful mpg gains!)