I have black soot on my tail pipe. And pretty bad mpg. At or about 13mpg consistently. Any ideas? No real mods. Just replaced the injectors with 4 hole.

 

Black soot is rich to much fuel . Did you get the right size injectors? and not larger ones ?

 

Could be the issue. I think they are Bosche 6 or 7 hole. What part number do you recommend?

 

When I did mine I used bosh number 0280155923 and It runs fine . and how good are your 02 sensors ?

 

I replaced all 4 of those not too long ago. They "should" be good.
Thanks for the tip on injectors. I'll try those and see.

 

What do your plugs look like? When I first got my 2001 XJ I put Iridium plugs in. 30k miles later they were roasted - white and burnt - indicating a lean condition. I went and put back in the OEM copper plugs. Right now I'm getting 15.4mpg (and I'm pretty heavy on throttle). For comparison sake - I have AFE cold air intake, BBK throttle body, and all new exhaust (including Banks Torque Tube headers). Hp and throttle response is very good and a lot better than when I first got it.

 

Motor is pretty much bone stock. 205k miles. After getting it, I've had to replace just about every sensor known, coil pack and plugs (AutoLite OEM), 4 - O2 sensors, etc. I did upgrade the injectors but noticed they're, I think, 7 hole. (I use readers and can't see chit LOL) there's more than 4 holes for certain. Blue colored Bosch with no ID numbers on the injectors. Idles fine but seems to have no get up and go at highway speed. Like it's lost its *****.
I'll check the plugs and try a different set of injectors maybe.

 

I can tell you the exhaust system and air intake/throttle body made a huge difference in power and crisper throttle response. The new exhaust headers probably have too, but it wasn't as noticeable of a change as the others. I still think I'm running lean, which I understand the stock ECU (or ECM) is programmed to do for fuel mileage sake. Hope just not as lean as I was before. I'll know in about 10k when I pull a plug or two and see what they look like.

Also, check and adjust the transmission kickdown cable. They need periodic adjustment and its super easy.