Poor mpg/ 4 hole injector mod

[TheBlueXJ]

So I'll start out with some information 4" rc lift 31" km2s stock gearing dent in downtube and new upstreap O2 sensor on 99 jeep xj with 165000 I'm getting around 12 mpg which is downright horrible I don't drive it like a NASCAR or anything so what can I do to help? I have been thinking about 4 hole injectors swap anyone done this iv also thought about fuel pump and pump filter any advice is great thank you all

 

[DieselSJ]

31's with stock gears isn't a combination for decent mileage.

What about the obvious stuff - plugs/wires/cap/rotor/air filter? What brand was the new O2 sensor?

 

[Digger87xj]

your speedo/odo is not correct with 31s if you didn't change the speedo gear. It'll be about 10% off.

 

[old_man]

Historically, from what I have seen, most XJ's get around 14-15mpg. Now if you add 33's with stock gearing and a lift, I would expect it to drop at least down to what you are getting. Also beware that with stock gearing, your speedo and odometer will be off as well, effecting the mpg you are calculating.

The best thing you can do is to gear it down to where the effective ratio is close to what stock was. You will have better acceleration and it will put the rpm's going down the road a lot closer to the ideal spot on the torque curve.

 

[MauriceGOL]

I did this mod. It certainly improved the rough idle, but I didn't see a lot of gains in MPG. Mine is also not a DD. If you have enough time behind the wheel to get the computer calibrated, perhaps yours will have better results than mine.

 

[Rockwood]

your speedo/odo is not correct with 31s if you didn't change the speedo gear. It'll be about 10% off.

Plus it's almost always in 3rd or bogging/slipping 4th unless perfectly flat or downhill.

 

[richslezak]

I did the swap and am getting lower mpg then before the swap. I also updated the intake manifold to 99+

I'm wondering if this JET stage 1 module would help with efficiency.
http://www.quadratec.com/products/17608_0111.htm

 

[xcm]

You cant just change to 4 hole injectors, and expect it drive like a V8... same is true with a 99+ intake...

Come on guys.... where do you hear this shit?

 

[richslezak]

You cant just change to 4 hole injectors, and expect it drive like a V8... same is true with a 99+ intake...

Come on guys.... where do you hear this shit?

Ha ha ha. I definitely noticed more low end power boost with the 99+ intake
I figured that with the new injectors, intake, banks revolver header and aem CAI I'm going to loose some mpg in exchange for more boost and stronger feel.

 

[skidtoy]

Boost...? Is there a snail or blower thrown in also?

 

[TRCM]

your speedo/odo is not correct with 31s if you didn't change the speedo gear. It'll be about 10% off.

Maybe......

I say this, cuz on my 96, with 31s & stock gears, the speedo is only off by 2 mph @ 55 by GPS. The speedo on mine was way off with stock tires.

I thought I was getting killer MPG, till I found this out one day messing with the GPS on my phone.

 

[TheBlueXJ]

so i plan on going to 33s and possibly 35s eventually should i gear to 4:56 how much do you think this will cost me to have the backlash and stuff set?

 

[dan1977p]

so i plan on going to 33s and possibly 35s eventually should i gear to 4:56 how much do you think this will cost me to have the backlash and stuff set?

I went 4.88 but I do a lot of mountain passes here and the 3.54's with 33's was almost undrivable. 4.88 on 31's may be way too much, though. I'm taching 3k at 80mph and it would only go up from there. If you are going to regear, I would do tires at the same time but that makes the cost go way up. But so does changing tire size and gears multiple times.

You never said the O2 manufacturer. Auto stores tend to push Bosch and the 4L doesn't like them for some reason. Using the NGK O2 sensor may help while you figure out your gearing. Gearing will definitely help, though.

 

[old_man]

4.56's with 35's will give you close to a stock overall gear ratio. That is what I have run for 10+ years, but I also run a stroker and an automatic.

I have never felt the need to gear lower on any of my crawling or on the mountain passes here in Colorado.

Jeep actually offered 4.56's on new XJ's and I have personally laid eyes on several of the mythical unicorns. 4.56 with a manual and 33's is good but with a manual, I would go with 4.88's on 35's. The downside is with D30's and D35's, 4.88 does not leave a lot of metal on the gears.

 

[richslezak]

Boost...? Is there a snail or blower thrown in also?

No I mean boost like the xj feels less sluggish compared to the older intake manifold and single hole injectors. Def picks up faster from standstill. I take it when I go on the trail going nice and slow I will have more power with a light touch of the gas pedal.

 

[Nichkojr.7]

I don't understand why people want their JEEP to perform like a race car, it's a jeep your gonna get bad mpgs to begin with, I will say I'd like to regear because I'm getting about 12 mpg on 33s and just cruising at a constant speed the rpms are at 2200 which sucks and is annoying lol