real_tree_camo_redneck

ok guys heres the deal i have a 99 xj this is my 7th xj my 2nd 99 sport ive had its gotta 3" lift 33s 180k miles it was running great gettin good fuel mileage till this one day it just started running ruff idleing low loading up dumping fuel at idle first thought was IAC sensor so i bought a new one and replaced it did nothing thought i might have got a bad sensor took it back got another one put it on same thing chanced of two bad sensors in a row is crazy well i live in sc no emission laws so the cat is cut off the rear O2 is unplugged and not there just like my last 99 xj ( never caused a problem other than check engine light)
i have all accel wires plugs rotor button distributor cap has a new header new muffler no exhaust leaks runs fine down the road the only time it messes up is after it warms up a few mins it idles low and choppy like it has a cam and loads up bad i can rev it very slowly up in rpm's it clears up off of idle and is fine till i get to 3000rpm's then it starts running very ruff again like it has a 2step almost poping and dumping fuel then i can smack the throttle and it blows black smoke out where its been dumping fuel or i can hold it steady at any rpm over 3,000 and its just fine its got me stumped

the only code it throws is P0128 bank 1 sensor 2 high voltage witch is the rear 02 sensor thats not there just like ive ran every xj ive had and it never caused a problem before

i can fill it up and get bout 125miles to a full tank no matter how i drive it any help would be great thanks guys

salad

Bank 1 Sensor 2 HIGH voltage does not mean it's missing, it means there's a short in your wiring harness that is sending battery voltage into a PCM sensor input. If left long enough this can destroy a PCM.

Might wanna track the fault down. Also please read the rules in this site regarding catalytic converter removal. It is illegal and discussion of such is not permitted.

Parsnip

First off, punctuation would have helped me read that. Secondly, your lack of a second o2 sensor is the reason it's dumping fuel. Lastly, prepare for the 'you don't have a catalytic converter' bashings.

Kingfisher

I've read the only purpose of the downstream sensor is to tell the condition of the cat.
I don't know!
Mine has never been hooked up since I've owned it
About 3 mos.
I notice no ill effects. Runs great!

salad

Depends on the year. 96-98 it doesn't appear to be, 2000+ absolutely the DS O2 is used in fuel trim calculations. '99 is a little ambiguous and I've not seen any conclusive test or documentation one way or the other.

At any rate that code needs a-fixin' before the PCM dies.

XJRed96

bank 1 sensor adjusts fuel trim rear o2 wont cause running issue. and a p0128 is a temp sensor/ thermostat fault not an 02 fault. a bad temp sensor could cause the problems you are experiencing.

XJRed96

this is from the jeep FSM..... "The upstream O2S sensor is located in the exhaust downpipe. It provides an input voltage to the PCM. The input tells the PCM the oxygen content of the exhaust gas. The PCM uses this information to fine tune the air/fuel ratio by adjusting injector pulse width.

The downstream heated oxygen sensor is located near the outlet end of the catalytic convertor. The downstream heated oxygen sensor input is used to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream sensor begins to match the upstream sensor input except for a slight time delay. By comparing the downstream heated oxygen sensor input to the input from the upstream sensor, the PCM calculates catalytic convertor efficiency

When the catalytic converter efficiency drops below emission standards, the PCM stores a diagnostic trouble code and illuminates the Malfunction Indicator Lamp (MIL). For more information, refer to Emission Control Systems."

.... in all the b1s2 or the second o2 sensor. or the downstream o2 whatever you want to call it is there to ensure the cat is working. this is not the cause he's dumping fuel especially if it's all the time such as when he first starts the car when the ECM is in open loop.

real_tree_camo_redneck

I've cut the cat off of every jeep I've ever had its never effected anything like this and let me point out that I've drove this jeep daily for 6-7 months with no cat on it before it started running like this

XJRed96

did you look into the coolant temp fault yet? check wires/connections or replace sensor? i agree that the rough running is NOT being caused by the cat or the b1s2 o2

XJRed96

i will concede to the fact that on the 2000 it does play a role in correcting A/F ratio but not on his 99

real_tree_camo_redneck

I'm gonna start swapping sensors off my 98 xj onto my 99xj till I figure it out I guess

XJRed96

start with the ECT probably the easiest one to do too.

real_tree_camo_redneck

I've had the problem fixed for a while now just forgot to post on here I broke down and bought a new O2 sensor and haven't had any trouble sence outa the 247 vehicles I've owned in my life 7 of them being xjs I've never had to replace and O2 sensor but that's what I did fixed the problem however check engine light still on and still tells me same code lol I still get crappy fuel mileage but not as bad as it was when it was dumping fuel I went from bout 6.5 mpg to bout 13-15mpg lol

XJRed96

so what is the fault? because a p0128 is not an o2 fault

zeecherokeeman

you owned 247 cars?are you 300 years old?