Hesitation and stall uphill

A little background...
99 XJ
201,000 KM (124,000 Mi) approx.
AW4
NO engine modifications
Plugs were changed about 5000 KM ago
Fuel pump changed about 10,000KM ago


She runs fine until it gets up to operating temp, and then she kicks sputters and dies (mostly going up hill). It'll fire up right away but dies shortly afterwards. If I let it sit for a while (5-10 mins) it'll start and drive fine for about 5-10 mins then dies out again. At idle, it's good but when I start driving it'll die.

Volts are at a constant 13.5-14
Oil pressure at the 3 on the gauge
Temp is dead smack in the middle where it should be
No abnormal smoke coming from exhaust, but it does smell like rotten egg when it's acting up and running rough.
CKP was changed today with no difference to how it runs

I was thinking bad gas, until I went to the last station of fill up and they said I was the first to report any issues.

Any ideas?

I did a search, but everything that I found came back as "bad CPS" sensor and as I already changed it, it's ruled out

Was the CPS replaced with a new unit from Jeep? Aftermarket sensors have spotty reliability and can cause driveability issues.

Also, is your upstream O2 sensor original? They have a typical service life of 100,000-150,000 miles and should be replaced as regular maint. If the issue presents itself once the vehicle is warmed up, that points to O2 in my opinion......Once in closed loop the PCM begins taking data from the upstream O2 to adjust fuel trim. A look at your short term/long term trims with a scan tool would be helpful in diagnosis.

Could also be a bad cat. You can crawl under the Jeep and gently bang on the cat. If you hear anything loose, replace immediately as the internal substrate has failed. You can also take a temp reading before and after the cat to see if there is a blockage.

98NWCherokee said:

Was the CPS replaced with a new unit from Jeep? Aftermarket sensors have spotty reliability and can cause driveability issues.

Also, is your upstream O2 sensor original? They have a typical service life of 100,000-150,000 miles and should be replaced as regular maint. If the issue presents itself once the vehicle is warmed up, that points to O2 in my opinion......Once in closed loop the PCM begins taking data from the upstream O2 to adjust fuel trim. A look at your short term/long term trims with a scan tool would be helpful in diagnosis.

Could also be a bad cat. You can crawl under the Jeep and gently bang on the cat. If you hear anything loose, replace immediately as the internal substrate has failed. You can also take a temp reading before and after the cat to see if there is a blockage.

Click to expand...

SOOO... I may have solved the problem... KNOCK ON WOOD.
My mechanic buddy had a theory; A simple one at that. I have to admit, it crossed my mind multiple times, but I never really gave it much thought. WATER IN THE TANK.
His theory was this..."Water is heavier than gas, right? WELL if its heavier, then it stands to reason that it will separate somewhat and sink to the bottom of the tank and on inclines or certain angles, it can slosh around and be moved around closer to the pick up inside the tank, causing it to be sucked up only at certain times. Such as when the vehicle is angled in a certain way."
This actually makes sence, SO I grabbed some STP Water Remover from the shell gas station, dumped it in the tank and filled it up with 89 as opposed to 87 (to help dilute and other remaining water in the existing fuel). I just got back from a 30-40 minute drive all around the countryside. Up and down hills, into ditches sideways and whatnot to cover as many angles as I possibly could. LOW AND BEHOLD, not a single stutter.
Lets hope that solves the mystery. Time will only tell....Thanks for all the suggestions!


I totally agree about the O2 sensor aswell. It's about time I change that while i'm at it. The new CKP is a mopar parts sensor aswell. I forgot to mention in my original post that I did crawl under and gave the cat a few decent smacks to see if there was any rattling inside it, and there was not.

did you replace the Crank position sensor with a Mopar Unit.. Or cheap Aftermarket parts store brand? I've replaced many Crank position sensors, and watched Non-mopars fail within 90 days.. Infact, its happened every time i bought Non Mopar Sensors..


Dont take this the wrong way.. But I laugh at "Mechanic buddy has a theory of water in the gas tank sloshing on a hill"

It's possible you have a failing Fuel pump.. Rent a Fuel pressure tester and report back!

3psi oil? That doesnt sound good either

20jeep00 said:

3psi oil? That doesnt sound good either

Click to expand...

thats NOT what he said:wave1:

NW-ZJ-SCOTT said:

did you replace the Crank position sensor with a Mopar Unit.. Or cheap Aftermarket parts store brand? I've replaced many Crank position sensors, and watched Non-mopars fail within 90 days.. Infact, its happened every time i bought Non Mopar Sensors..


Dont take this the wrong way.. But I laugh at "Mechanic buddy has a theory of water in the gas tank sloshing on a hill"

It's possible you have a failing Fuel pump.. Rent a Fuel pressure tester and report back!

Click to expand...

BOTH CKP and Fuel pump are Mopar original parts. Fuel pressure reads at 48 PSI at idle consistently every time I take a reading.

I've had no issues with it since putting in the water remover and fueling up with a higher octane fuel...YET.