XJ Jeep help requested

Hi all..

I have a '98 Cherokee with 150k miles which almost none are highway. It has never let me down and is the most reliable vehicle I've ever owned. It always runs ok but is usually pretty slow (stick shift, stock 3.07 gears and 31" mud tires...go figure )

My question is this; when the air temperature gets much above 90F and I have the AC on (I don't know if the AC is a contributor or not), the throttle response becomes much improved. That's right IMPROVED. It's almost as if the computer switches to another map when it's hot.

What is wrong with this machine that it won't run like this all the time? Today is one of the hottest days in the last few years and when I backed out of my driveway I actually spun a wheel. I wasn't driving any differently than I usually do.

Thoughts?

It's weird I know

That is weird and I don't have an answer. You might try the Jeep forum of NAXJA forum for further help. I also have a Jeep Cherokee and wish that would happen!!

Check your thermostat, coolant temp and intake air temp sensors. It could only be warming up(or thinking it's warmed up) to closed loop on really hot days with the added heat of the AC.

Even on 31s the 4.0 should be plenty of power, they make around 200 hp stock and more torque. I'd agree that something is up, also check the maf meter, I had one go bad on a ford that never threw a cel but ran fat, got bad mileage, and went through cats every year or so.

Yup, check t-state and coolant temp sensor. It sounds like it only only running right when it's hot. I bet you are getting piss-poor fuel economy, like 10-12 I bet.

no maf to check. make sure it is reading temp right that thermostat isnt stuck open. even on 31's that jeep should not be lacking on power. i had a cherokee on 31's that never had power issues like that.

Even by 98 they weren't using a maf? I may be confusing it with another truck but I though they had one in the throttle body

Jeep never put a mass airflow sensor on the 4-liter.

Hell, Chrysler only recently started using them on anything!

mileage is about the same as others with this same rig. 16 around town and maybe 20 if it's babied on the interstate.

if the stat was stuck open then it would never warm up in the winter. I've never had that issue.

to all those who say it shouldn't lack power, i bet your's was an automatic. autos got 3.55 gear and the torque multiplication from the torque converter. autos feel noticeably faster

Hell, Chrysler only recently started using them on anything!

Which is nice because in ten years you didnt have to buy a dealer only intake tube to get it to run right.. Maybe the materials have improved by now but it's apparent that every japanese manufacturer used the same E36 M3ty stuff on their intake tubes for over a decade.

I agree that the jeep probably has had a long-standing issue affecting power that you didnt notice. My friend ran his 5spd/3.07 jeep on 29"s at the track and ran 16.0@85, probably could have broken 15.9 with practice. Yours should still be in the 16s which people on THIS forum generally dont think is that slow.

Also, i disagree that autos feel faster, and ive owned 4. They feel punchier in first gear, but the faster you go, the slower they are compared to the 5spd/3.07. Granted, i might be the only weirdo that gets in a cherokee and floors it up to 90+ mph to comment on the higher speed acceleration.

I can only echo what others have said. Find the ohm charts for your CTS and IAT and see if they're reading right.

Carro Atrezzi wrote: mileage is about the same as others with this same rig. 16 around town and maybe 20 if it's babied on the interstate. if the stat was stuck open then it would never warm up in the winter. I've never had that issue. to all those who say it shouldn't lack power, i bet your's was an automatic. autos got 3.55 gear and the torque multiplication from the torque converter. autos feel noticeably faster

I've had many Jeeps and they have had no problem at all with 31's. My first Jeep had a 4 banger (4.11 gears) and 33's and it was better than what you describe. Check the TPS sensor resistance with it's cold, then put it in a 200* oven for 5 minutes and check it again. See if the resistance is different. Stock your jeep had 27's or 28's so 31's isn't much difference really. Do you know of anyone with a similar year Jeep you can swap ECM's with?

I once chased down a LS integra on lime creek road in Austin in a 5spd 4.0 wrangler. They have plenty of power even with a stick.

maybe you guys are right. I just can't believe I've driven it 130k miles (had 20 when I bought it) and it has never thrown a CEL.

I will admit to having lost a handful of stoplight races to Wranglers. They are fun and i want one. Too bad they hold their value so damn well.

Carro Atrezzi wrote: maybe you guys are right. I just can't believe I've driven it 130k miles (had 20 when I bought it) and it has never thrown a CEL.

If it thinks the engine is cold, it will stay running open loop and never know anything is wrong. A car with a stuck T stat can still "warm up" in the winter. Does it have a known good temp gauge and sender?

Kenny_McCormic wrote:

Carro Atrezzi wrote: maybe you guys are right. I just can't believe I've driven it 130k miles (had 20 when I bought it) and it has never thrown a CEL.

If it thinks the engine is cold, it will stay running open loop and never know anything is wrong. A car with a stuck T stat can still "warm up" in the winter. Does it have a known good temp gauge and sender?

I dunno, he seems resistant to think it could be anything we (the people he's asking for help from) are suggesting. I partially stuck t-stat can allow heat in winter but keep it in open-loop, a temp sensor will keep it in open loop. An ECU could do anything it wants. I t-stat is cheap insurance and I'd have done it already just because it's suspected.
If you do a t-stat, make sure you bleed the air from the system. When you are refilling the coolant, remove the hose that goes from the t-stat housing to the heater core. When you see coolant coming out of the t-stat it's bled.