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Jeepster19
05-16-2009, 08:48 AM
Has anyone ever had their xj to get good gas mileage one tankfull and then crappy mileage the next?The driving conditions are the same so I dont really understand what is going on!I may try to replace the o2 sensors and see if that helps,but I am going to put it on a scan tool to see if they are in spec.Any input would be greatly appreciated!!!:thumbsup:

BlueXJ
05-16-2009, 10:54 AM
Check that your air filter is clean and not obstructed.

Jeepster19
05-16-2009, 12:17 PM
I installed a k&n fipk about a month ago,looks clean.:thumbsup:

Mudderoy
05-16-2009, 03:20 PM
Has anyone ever had their xj to get good gas mileage one tankfull and then crappy mileage the next?The driving conditions are the same so I dont really understand what is going on!I may try to replace the o2 sensors and see if that helps,but I am going to put it on a scan tool to see if they are in spec.Any input would be greatly appreciated!!!:thumbsup:

If you don't have a check engine light then you won't have any codes.

What was the good gas mileage, what was the bad?

Was the outside temp radically different? I'm down almost 1 mpg because I am running the air conditioner and it is in the 90's outside.

xjjeepthing
05-16-2009, 03:53 PM
Temp. and humidity can effect mileage. So can fuel from different stations. If one tank has less alcohol in it, it will get better mileage. The higher percentage of alcohol will get less mileage

Jeepster19
05-17-2009, 05:23 PM
I'm going to try the gas thing,maybe look at a few different places where I fillup&use the one with the least amount of alcohol.I am going to put the factory air box back on tomorrow,as I have to go back up to winston salem on tuesday.I got roughly 19mpg on the highway with the k&n fipk and the magna-flow cat-back exhaust system.I also replaced the converter.:)

2000XJ
05-19-2009, 03:35 PM
I've had this sporatically happen to me. I file it under "it's a Jeep thing", and just keep going.

Jeepster19
05-20-2009, 08:25 AM
I just got back from my trip to winston salem and checked my mileage when I got back in town.It was a amazing 24mpg!!!I filled up with shell gasoline in nc on the way back,regular grade was used.I don't know if it was the gasoline or the new converter and magna-flow cat-back system or maybe both,but I am pleased with the outcome!Cruise control was set at 70mph and I am running 30x9.50's.:D

Mudderoy
05-20-2009, 08:54 AM
Well I'd say it is working well if you are getting 24 mpg, but I'm curious how are you calculating your mpg? Is your speedometer corrected for the larger tires?

Jeepster19
05-20-2009, 12:32 PM
Yes.I'm going to try another full tank of shell gas and see what it get's around town.I topped off when I got back so it has a mixture of shell&hess gas in it.Going to change the o2's out shortly,they need it with 150k.;)

Mudderoy
05-20-2009, 12:39 PM
Yes.I'm going to try another full tank of shell gas and see what it get's around town.I topped off when I got back so it has a mixture of shell&hess gas in it.Going to change the o2's out shortly,they need it with 150k.;)

I would advise you NOT to change the O2 sensors. At 24 mpg (if that is verified) everything is working VERY well. Don't mess with it if it isn't broke! :driving:

dok1313
05-20-2009, 01:27 PM
I have always been a fan of Shell gas. People always say "gas is gas" but tha't not true at all. You might pay a couple cents more, but totally worth it.

Jeepster19
05-20-2009, 01:40 PM
It's worth every penny!!!I wish I had done this earlier,live and learn I guess.:D

BuckB91XJ
05-24-2009, 02:27 PM
I've changed my tire size and gear ratio a couple of times over the time I've owned my XJ. I've found that if I keep my rpm at or as close as possible to 2500 rpm while on the Hwy. cruising, I get my best fuel economy. Even with 4.56 gears, lifted 6" and running 33" tires. I can get 20 mpg on the highway if I keep it at 2500 rpm. This about 70 mph.

pLEXX
05-24-2009, 02:42 PM
mud your lieing its in the 100's :/ and also, shell has the best gas mili, for dodge,Chrysler, and jeep :]

mizedog
05-26-2009, 10:29 AM
I've found that if I keep my rpm at or as close as possible to 2500 rpm while on the Hwy. cruising, I get my best fuel economy. Even with 4.56 gears, lifted 6" and running 33" tires. I can get 20 mpg on the highway if I keep it at 2500 rpm. This about 70 mph.

I hope you're right about this! I just changed to 4.56s last week, put a 39 toother in (in anticipation of 33s). With my current 32s, I've only gone 65 miles and it's down well below 3/4 of a tank. I'm hoping that it's a gauge issue (not a flat curve...). I will say that with the Rusty's intake and manifold spacer, the Check Engine light comes on for a week or so here and there. It came on last Friday. This may be due to the weather change (cold and rainy for days).

I'm hoping I'll top 15 mpg on my trip to SoCal. But I have to admit, that Flowmaster 40 gets LOUD at 65mph (can you say UPS truck?). I may drive it like a grandpa.

Mudderoy
06-22-2009, 09:48 AM
I was recently digging around on the Internet and I found a article about XJ gas mileage. They were doing different things (one thing at a time) driving the XJ a minimum of 500 miles and recording MPG.

They were doing fine with their MPG and all the sudden it dropped to 13 to 14 mpg. They hadn't make a change. Shortly after the mpg drop the belt started squealing. The power steering pump locked up on them. They replaced it and the mpg jumped back up to the 17 to 18 mpg they were seeing before.

I've had a problem with my power steering pump for years. If I take a corner too fast it starts whining. Maybe this is normal when the fluid is low, but it seems mine does it whether it is full or not.

I am considering changing my power steering pump.

Just a FYI...

Audio222
06-22-2009, 02:41 PM
I've had a problem with my power steering pump for years. If I take a corner too fast it starts whining. Maybe this is normal when the fluid is low, but it seems mine does it whether it is full or not.

I am considering changing my power steering pump.

Just a FYI...


My power steering pump makes the same noise. I would be interested to know if changing it would make a difference.

Mudderoy
06-22-2009, 02:44 PM
My power steering pump makes the same noise. I would be interested to know if changing it would make a difference.

How's your gas mileage?