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No High End Power or on Hills

F

FU-UR

NAXJA Forum User
Location
USA
My 99 5-speed 4.0 (120k miles, no oil leaks, no oil burning, recent tune-up) dogs our terribly on hills when I'm in 4th or 5th gear. It's the worst on the highway (and I live in CO). I have to shift down to as much as 3rd gear to get it back up to 65 while on a big hill. It does the same in town on steep stuff in 4th or 5th. It's also nearly impossible for me to go over 75 on flat roads. My tires are 30" and I have a 2" lift.

There really are no issues with the car other than the idle fluctuates slightly at rest due to a dirty ICM. The throttle body is clean. I have a K&N filter and 2" custom exhaust all the way back. There is a little glug-glug sound when decelerating in 4th-2nd. But that's really it.

Any ideas on what's causing this?
 
FU-UR said:
Thanks for the info, I need to see where the heck that is in my FSM.
Click to expand...
I'm pretty sure it's on the Firewall just above the intake manifold: check the vacuum line that goes into the TB for cracks.
 
Was your XJ originally purchase NEW in Colorado? The higher elevation XJs came with a CPS that was advanced a couple degrees to give the engine better power. You can either check at the dealership OR purchase one from Turbo City who markets RockIt parts. They offer a CPS that is advanced a couple degrees due to a slotted bolt hole.
Over the years since I purchased my 98 XJ NEW in 97.... I have added a K&N FIPK, Gibson catback exhaust, Gale Banks header, JET Stage 2 Performance Chip, Turbo City enlarged throttlebody, Accel cap & rotor, MSD-6A ignition & plug wires, and changed all lubricants to synthetic....
Performance is GOOD...., but have considered purchasing the newer style 99+ intake manifold for a little more Torque/HP.
In case you are curious.... With all these modifications; at 88K the engine emissions are OUTSTANDINGLY low.....

Charles
 
Last edited:
ScoobyXJ,

My 98 XJ came with a 1 3/4" exhaust (approximately) and I upgraded to the Gibson 2.5" catback exhaust.
Quite a noticable difference in performance....

Charles
 
The car was purchased in Seattle, so you may be on to something with the CPS, although I don't know what that stands for. What is it, exactly?
 
CharlesS said:
ScoobyXJ,

My 98 XJ came with a 1 3/4" exhaust (approximately) and I upgraded to the Gibson 2.5" catback exhaust.
Quite a noticable difference in performance....

Charles
Click to expand...

Then that must have been one of the changes in 2000, 'cause mine has 2-1/4" from the muffler to the tailpipe. The piece from the headder to the cat looks to be at least 2-3/4" if not 3" too.
 
ScoobyXJ,

With emissions changes by the Fed Govt; Chrysler had to make changes to the engines to meet the requirements and these changes decreased the performance of the engines. Chrysler modified the intake manifold capacity, fuel/air ratios, exhaust, dual catalytic converters, and cam profile to bring the performance slightly above what it was prior to the emissions changes....
The exhaust diameter increase was one of the changes....

Charles
 
FU-UR said:
My 99 5-speed 4.0 (120k miles, no oil leaks, no oil burning, recent tune-up) dogs our terribly on hills when I'm in 4th or 5th gear. It's the worst on the highway (and I live in CO). I have to shift down to as much as 3rd gear to get it back up to 65 while on a big hill. It does the same in town on steep stuff in 4th or 5th. It's also nearly impossible for me to go over 75 on flat roads. My tires are 30" and I have a 2" lift.

There really are no issues with the car other than the idle fluctuates slightly at rest due to a dirty ICM. The throttle body is clean. I have a K&N filter and 2" custom exhaust all the way back. There is a little glug-glug sound when decelerating in 4th-2nd. But that's really it.

Any ideas on what's causing this?
Click to expand...

This sounds like a classic case of a plugged cat. Bash it with your fist while it's cold. If you hear it rattling like a can of marbles, it's time to change it. You can find a Carsound 2.5" high-flow cat cheap in e-bay.
 
CharlesS said:
ScoobyXJ,

With emissions changes by the Fed Govt; Chrysler had to make changes to the engines to meet the requirements and these changes decreased the performance of the engines. Chrysler modified the intake manifold capacity, fuel/air ratios, exhaust, dual catalytic converters, and cam profile to bring the performance slightly above what it was prior to the emissions changes....
The exhaust diameter increase was one of the changes....

Charles
Click to expand...
So I wonder where that leaves me. I have the newer intake (I think anyway), no pre cats, no pinch in the down pipe, and the larger exaust. I can't tell you about anything else on your list 'cause I don't know. Hell I ought to go look to see if I got lucky, and got the 0630 head. I do remember that when I put a Flow Master 40 series on it it made quite a noticeable difference.
 
ScoobyXJ,

Have to agree with Dr. Dyno..... Verifying the condition of the catalytic converter to see if it is plugged is certainly worth checking into.
This can be done a most muffler shops by drilling a small hole in the exhaust pipe before and after the catalytic converter to check the pressure drop across....
Should be a minimal pressure drop....

Charles
 
Another vote for a clogged cat.

The high altitude CPS was only for the Renix years, 86 thru 90. There is no high altitude CPS for a 99.
 
I appreciate everyone's input on this. I had a chance to take a close look at the vacuum tubes and they are all good. The cat did not sound like a can of marbles when I spanked it cold.

But, I will take your multiple advice on that and get it swapped out.
 
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