2000 XJ Slowwww

First off
2000 with coil rail distributor-less ignition system. 4.56 gears and 265 tires (32") 232k miles roughly 90k on engine block.

Jeep runs like an unmotivated turtle. Below 2k rpms has decent power anything above that it is gutless. Partial throttle gives same response as full throttle.

In the past 1k miles has had new TPS, CPS and IAC. MAP tests fine. Fuel pressure bounces from 45-49psi while idleing and is dead on at 49 when pushing the throttle in park. Fuel pressure does not drop off after shutdown-not a bit. Has APN Header and exhaust was redone from header back with a new muffler last year. o2 sensors in good shape. No codes, idles fine and climbs rpms fine. Runs great just doesnt have any power. Compression is 140 with one cylinder being 135 and one being 145. Air filter is fine.

I've read through tons of pages of threads-most end up with a clogged cat. I've removed that and fitted a straight pipe to try and narrow down the solution. My fuel pressure seems to be perfect. This jeep has run a lot better in previous years-ive owned it since new just havent driven it regularly for the past few years. Sold wifes car and she had to drive it for a few weeks this fall and haven't been able to track down the cause.

I've questioned the fuel synchronization needed for the 2000+ ignition systems, but the plugs are colored correctly like its running right. I think i might be down to the torque converter (and i have checked the brake switch). When sitting parked for awhile the jeep has to rev a bit to get it to move. When going down the road and you let off the gas the jeep de-accelerates quickly. It feels as though its braking but the brakes aren't grabbing i checked them. Jeep shifts fine when moving. TCase was rebuilt a few years ago and chain wasnt in bad shape.

Fuel Pump is original, so is the coil rail so ive also questioned both of those-but they both have indications that they are still operating properly. I'm out of ideas on how to narrow this down. Any help?

I think your over geared, those gears are best for 33" and up. My opinion though

I'd keep an eye on fuel pressure. Get it set-up so you can watch it and drive it while under load when fuel consumption is highest.

The fuel pressure regulator on top of the fuel pump module doubles as a filter and like any other filter, can become clogged. Being original, with 235k, it's highly suspect.

Demonoid369 said:

I think your over geared, those gears are best for 33" and up. My opinion though

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Curious as to what measures are required to get the PCM to work correctly with that gearing in the late model XJs.

OP--you might want to move this to MOD tech.

Well he's at 32" with 4.56 gears, he's going to be in the upper rev range driving because of it which would explain why when he lets go of the gas he gets that drag effect from the engine, kinda like a engine brake effect

sorry need some clarification-gears have been in for 3+ years with this tire size. Just gave that info because it should be moving along with less effort. I actually love the 4.56's and 32's and didn't have a problem with the engine not liking the combination in the past. It's even better offroad (when working correctly).

I'll get a fuel pressure setup i can watch while i drive, thats a very logical next step. Driving it around today it FEELS like the exhaust is completely clogged. I'm noting that as that's the best description of what im experiencing i feel as though i've eliminated that side of things pretty well with the steps i've already taken.

StylerG said:

sorry need some clarification-gears have been in for 3+ years with this tire size. Just gave that info because it should be moving along with less effort. I actually love the 4.56's and 32's and didn't have a problem with the engine not liking the combination in the past. It's even better offroad (when working correctly).

I'll get a fuel pressure setup i can watch while i drive, thats a very logical next step. Driving it around today it FEELS like the exhaust is completely clogged. I'm noting that as that's the best description of what im experiencing i feel as though i've eliminated that side of things pretty well with the steps i've already taken.

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3+ years of driving up in the higher rpm range can do damage over time. People tend to love being over geared because its quick off the line and great on trails but daily driving at highway speed, your rpm I wouldn't be surprised if its in the 2500-3000 range at cruising speed. Which could over time wear parts out a lot. But again that's just my experience with vehicles.

Demonoid369 said:

3+ years of driving up in the higher rpm range can do damage over time. People tend to love being over geared because its quick off the line and great on trails but daily driving at highway speed, your rpm I wouldn't be surprised if its in the 2500-3000 range at cruising speed. Which could over time wear parts out a lot. But again that's just my experience with vehicles.

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im sure you have valid experience with this. This for the past 4+ years has been a trailered trail rig driven occasionally around town. A conservative guess is it gets 1,000 miles/year

with that said I'm up for checking anything out-so what parts would you suggest i look at that would be worn from my setup that point towards my problems? I've run the end of my rope time to start looking outside of my knowledge base on it.

It really does sound like a plugged cat but with that already eliminated as a cause, I'm not sure what to check next... did you try running it with the exhaust open where the cat would be normally before installing the pipe? Perhaps half the cat core ended up in your muffler and plugged it, like what happened to my 91 MJ a few months ago.

I'm interested to see what fuel pressure readings are, having just solved my own lack of power/bogging @ 2k issues.

StylerG said:

This for the past 4+ years has been a trailered trail rig driven occasionally around town. A conservative guess is it gets 1,000 miles/year .

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now i didnt know that lol trailer changes it lol like kastain said, check your muffler for debris that might have came from the cat, might be causing excess back pressure then.

Have you adjusted your throttle cable?

Have adjusted throttle cable. I'll try and get the fuel pressure readings tonight seems a good first place to start though it involves removing the c-rok bumper and skid if thats the problem

Hadn't thought of debris in the muffler. I can easily disconnect the header and run like that for a few blocks till I get pulled over. I'll let you know what I find from those two things.

If it has the Cali emissions package don't forget that there are 2 "upstream" cats right below the exhaust manifold. I would assume that these can get clogged too...

StylerG said:

Have adjusted throttle cable. I'll try and get the fuel pressure readings tonight seems a good first place to start though it involves removing the c-rok bumper and skid if thats the problem

Hadn't thought of debris in the muffler. I can easily disconnect the header and run like that for a few blocks till I get pulled over. I'll let you know what I find from those two things.

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:yelclap:

Its your cat. Same thing happened on my old 93.

for those wondering-i do not have the extra converters because mine is not a cali emissions. So the cat has been eliminated.

Driving with a fuel pressure gauge zip tied to my windshield wiper tonight and through my hood vents i noticed something. For about 20 minutes under load it ran at 49psi. I shut the jeep off and went in a gas station, came back out it was 32. Started the jeep up and the fuel pressure didnt climb, after a few miles on the interstate it still didnt climb until i let off the gas and coasted. After doing that in normal driving for the next few miles it was right back at 49psi and remained there even after i shut the jeep off at home. let the gauge set for a bit and pressure didnt drop.

So best guess on my end is a bad filter on the assembly that gets partially clogged??? Either way its replace entire assembly-unless anyone can convince me thats normal operation procedure.

Interesting.

Factory fuel pressure on your rig is 49psi +/- 5psi.

Looks like yours is running right at spec. Also, if it DOESN'T go down after shutting it off, that's a good thing, because it means that the system is staying pressurized allowing for a quick couple crank fire-up in the morning after sitting overnight.

That's what I interpret from the data you gathered. Maybe someone else can chime in.

Personally, for me, that would rule out a fuel supply issue. I would move onto your spark. Quality, duration, correct plugs, coil not taking a dump on you, etc, especially if you have no Cat to clog.

(my dad taught me it's usually fuel or fire, when a car's not running right. )

SanDiegoOverland said:

Interesting.

Factory fuel pressure on your rig is 49psi +/- 5psi.

Looks like yours is running right at spec. Also, if it DOESN'T go down after shutting it off, that's a good thing, because it means that the system is staying pressurized allowing for a quick couple crank fire-up in the morning after sitting overnight.

That's what I interpret from the data you gathered. Maybe someone else can chime in.

Personally, for me, that would rule out a fuel supply issue. I would move onto your spark. Quality, duration, correct plugs, coil not taking a dump on you, etc, especially if you have no Cat to clog.

(my dad taught me it's usually fuel or fire, when a car's not running right. )

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Read again:

I shut the jeep off and went in a gas station, came back out it was 32. Started the jeep up and the fuel pressure didnt climb, after a few miles on the interstate it still didnt climb until i let off the gas and coasted

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Could the FPR, or a voltage drop, loose electrical connection or changing ground to the fuel pump.

IMPO (26 years in the biz) replace the fuel pump module... the whole shebang. Stay away from airtex unless you want to change it again in less than 10k miles.