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Odd gas saving mod...

E

el_roy1985

NAXJA Forum User
Location
Bismarck, ND
Not sure how this works, but when I did it, I surely received the best tank of fuel ever since acquiring my XJ. My speedometer is off from tires and gears (33/4.56), but I still keep track of how far it gets me per fill. Usually, I end up somewhere between 160 to 180.

I then decided to see what others were getting with similar setups. Where was at, is much below what I should be getting. With 160,000 miles, I decided to do the O2 and cap/rotor. I had already done the plugs/wires, but overlooked the cap/rotor at the time because I'm too used to distributor-less ignitions. The old cap/rotor were horrible, and I have no idea how the old O2 sensor was by just looking, but I'm sure it wasn't as good as it should be after all these years and miles.

After performing the tune-up, it definitely ran smoother. This had me anticipating a decent increase in MPG. However, after some time, I noticed that my fuel saving was negligible. I then decided to finally take it in for the PCM reflash that was issued for my 1996 XJ. Afterwards, It started much quicker and idled smoother. So it helped , but still no fuel savings was noticed.

It wasn't until I performed what I will picture next, that I received not the measly average of 175, but a little over a whopping 220 miles to a full tank. Well, here is the answer to the mystery...
 
2011-10-12_134207.jpg


I don't really understand it, but a few hundred pounds of bricks really increased my fuel economy. I could definitely feel the weight while it was in there, but the performance of the vehicle was impacted minimally. I had these in there for almost the entire tank of fuel, only very little of it was driven unloaded. It was also mostly in town stop and go driving.

Only thing I can think of is that maybe it was because it slowed me down a bit. Even though the engine worked harder, it must have worked more efficiently. I usually drive pretty conservatively, but this is all I could think of, because it would slow my normal driving down even more.

At least I know I don't have to worry about adding a bit of extra weight to the XJ. It handles it without a problem, and seems to like it?
 
So i guess if you put more in you would do even better right? So by extension, if you chained it to your house, it would be like a Prius? ;)

Actually, it probably took a couple of hundred miles for the ECM to have enough information from you O2 sensor to help things, up until then the old information was still in the ECM.
 
So your telling me all the armor, bumpers, skids and lift kit and whatnot im throwing on my jeep is helping it save fuel!? :scared: MUST BUY MORE CRAP FOR JEEP!
 
Begster said:
I'm sorry, but I call utter SPOBI.
Click to expand...

Not sure what that is.

It was actually almost a year later that I hauled this load. Just thought it would be an odd story to share. Fuel filter and possibly fuel pump is on the list to replace this year, and possibly plugs and wires again. Hopefully my biggest fuel improving mod will be working soon, which is my car.
 
SPOBI is what you say when someone claims ford 8.8's came in jeeps baring the offroad package, "stop posting bad information'.

The OP nailed it in his first post... he drove slower due to being loaded down, YES, the bricks put more of a load on the motor, and he lost mpg here... however, the xj gains more aerodynamic drag the faster you drive... so going slower gained him more mpg then he lost due to added weight...

To sum it up:
Driving slower = better mpg
Driving weighted down = doesnt help, most likely hurts.
 
el_roy1985 said:
Not sure how this works, but when I did it, I surely received the best tank of fuel ever since acquiring my XJ. My speedometer is off from tires and gears (33/4.56), but I still keep track of how far it gets me per fill. Usually, I end up somewhere between 160 to 180.

I then decided to see what others were getting with similar setups. Where was at, is much below what I should be getting. With 160,000 miles, I decided to do the O2 and cap/rotor. I had already done the plugs/wires, but overlooked the cap/rotor at the time because I'm too used to distributor-less ignitions. The old cap/rotor were horrible, and I have no idea how the old O2 sensor was by just looking, but I'm sure it wasn't as good as it should be after all these years and miles.

After performing the tune-up, it definitely ran smoother. This had me anticipating a decent increase in MPG. However, after some time, I noticed that my fuel saving was negligible. I then decided to finally take it in for the PCM reflash that was issued for my 1996 XJ. Afterwards, It started much quicker and idled smoother. So it helped , but still no fuel savings was noticed.

It wasn't until I performed what I will picture next, that I received not the measly average of 175, but a little over a whopping 220 miles to a full tank. Well, here is the answer to the mystery...
Click to expand...

where is the pcm and where did you take it to do what you had done.
 
No idea where it is, never looked for it before. Just went to the dealership and they did the flash, free of charge. It's a recall, pretty sure it has something to do with the fueling.

At the speeds I was driving, I don't know that aerodynamic drag had much to do with it. I'll just call it a weird coincidence. Sure hope no one would take it as a real way to improve fuel economy, that would be daft.
 
If it was the E22 recall, it was to fix an issue that could cause the computer not to notice when the cat goes bad. I had mine done a few years ago and got a free cat out of it since the existing one was bad at the time...:D
 
It wasn't the bricks, it was your change in driving style and maybe the ECU picking up a better tune as it learned after the reflash.

I pulled 23mpg in my stock MJ with 1500lbs of cargo, summer gas, stock 225/75r15 tires, 3.55s, 215 thousand mile AW4 and 4.0 (both with no rebuilds in that time). Why? I kept it to 55-65 and was on the highway for an entire tank of gas. Yes, this is based on amount added at the pump after starting the drive with a full tank, and yes, I checked my odo accuracy.

I got under 16mpg on the way down for the same trip. Why? I was doing 80 the whole way. Same exact load, except some of the burgers and beer hadn't been consumed yet.
 
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