00 XJ Sport running weak?

I have had three XJ's so far - a 90 Pioneer, then a 96 Country and now my 00 Sport. The 90 got the best gas mileage at around 24 mpg and decent power, even at 160k miles. The 96 got poor mpg (15/18 that I attibuted it to the trac-loc and 140k) but it had good power. The 00 (with only 45K) gets marginally better mileage averaging 19-20 mpg combined but the thing just lacks the punch. The latter two had the same 3.55's and I switched the 235/75/15 tires from one to the other. As for mods, they are limited to the 96 having a Rusty's flowmaster aftercat exhaust and aftermarket header and 3 row radiator. They weren't on for long before I traded to the newer model. I have yet to touch the 2000. I changed the plugs to Champion Gold Truck Plugs and replaced the air filter but it didn't help. I was going to replace the wires, dist. cap and rotor until I found that there were none to replace. I have used Lucas Oil fuel additive regularly. It does have it's moments of running well, but generally only when it is cool and dry. My only guess at this point, barring any major interanl mechanical problem, is the engine is restricted severely on the intake an exhaust. My reason is the slowness in getting the engine to rev quickly. Any thoughts?

the exaust us relativly high-flow, unless your upper control arm/rock has smushed the tube together.

I had no exaust-system, virtually streight pipe, for a month (problem mentioned above, cut it open till fix), and noticed only small diffrences in preformance under diffrent operationl conditions. Of course, that could be bias because i couldn't hear anything.

OTT,when in doubt, change all the fluids.

Regards,
jeremy

Change the plugs underneath the coil packs? I run Bosch platinum +4's and noticed a differance... also I am running straight pipe exaust,Its really not that loud ! I noticed more power through all rpm. also homemade intake tube w/K&N cone filter , Change all fluids... my 2ooo's been on Mobil 1 since birth everywhere even Grease. also try filling it up with premium gas and pour in a bottle of fuel injector cleaner. (I prefer Valvoline synpower)
Try that !

Rob B
Y2K-XJ
4" 32's soon some cool stuff and other things...

Other than the obvious environmental concerns, did you loose torque with that set up? I've always been told that the 4.0L needs a certain amount of back pressure to produce torque.

Vertigo said:

The 00 (with only 45K) gets marginally better mileage averaging 19-20 mpg combined but the thing just lacks the punch.

Click to expand...

Gee. What I'd give for my 2000 (also stock, and on 235/75 tires) to get
something close to 20mpg in day-to-day driving. I get a hair over 20 on
all-highway trips... more like 17-18 in my normal mix.

I've found that the 2000+ 4.0 seems really picky on what brand of GAS I use.
With cheapies, it starts harder, idles rougher, seems to have less power, and
is generally unhappy. So I try to stick to the BIG name brands (normally
Exxon... sometimes BP). I had some Sunoco for a couple of tanks, and the
thing was VAPOR LOCKING on me... hard-start and sputtering badly if I tried to start it while hot...

Den

DenLip said:

Gee. What I'd give for my 2000 (also stock, and on 235/75 tires) to get
something close to 20mpg in day-to-day driving. I get a hair over 20 on
all-highway trips... more like 17-18 in my normal mix.

I've found that the 2000+ 4.0 seems really picky on what brand of GAS I use.
With cheapies, it starts harder, idles rougher, seems to have less power, and
is generally unhappy. So I try to stick to the BIG name brands (normally
Exxon... sometimes BP). I had some Sunoco for a couple of tanks, and the
thing was VAPOR LOCKING on me... hard-start and sputtering badly if I tried to start it while hot...

Den

Click to expand...

Hi,
Just wanted to comment that I have had the same results with my 2000 and different brands of gas. When I stick to Shell and 76 I get 23MPG highway. If I use anything else (which around here is Arco and Chevron) it drops to 18 or 19 and runs way rougher...
Just my 2cents..