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oxygen sensors and or a pcm reflash?.....

moparjim1987

NAXJA Forum User
Location
pennsylvania
Some of you might remember my ranting posts a few months back about my 97 xj running rough after i drove it for a while, and coughing/sputtering when it is accelerating from a stop. well, i put in a new oxygen sensor and it was fixed, until now. my fiancee and i just took a weekend jont to linwood in northern ohio from indiana PA, and the round trip was close to 500 miles. in addition to finding that my v.c. gastet leaks bad enough to splash oil out onto the exhaust and make it smoke like a bandit going down the road, it has started the sputtering thing again. now for my question, do oxygen sensors go bad that quickly, or do i need my pcm reflashed? the truck now has 166,000 miles on it, and i have already replaced quite a few other sensors and switches, with the oxygen sensor being the culprit. now, i havent replaced the downstream, or put the heat shield stuff around the #3 injector, but that might be it, i don't know. if someone has an idea as to what my problem might be, i'd sure appriciate hearing what you have to say, and if someone could post the link for the t.s.b for the injector fix that'd be great. and sorry for the novel.:huh:
 
Don't know what the answer to your problem is but its nice to hear from someone on here that lives close by. I'm from Punxsutawney.
 
I doubt that the PCM is the culprit. O2 sensor failure would be reported by the PCM via your CEL.

Started after your trip? Did it actually die at some point?

If your leaking enough oil to cause the engine to smoke I'm wondering if the CPS is covered with oil too. Fix your oil leak and pull the CPS and see if there's a bunch of oil/crud on it. Then again an intermittant loss of Cam or Ckrank signal is reported via the CEL too (Code P1391).

Any other work done recently?

Does the problem happen when the engine is cold or only when it's warm/hot? Will the problem occur if the vehicle is not moving?
 
The coolant temperture sensor on the thermostat housing may be giveing a incorrect voltage reading. It may be wrong enough to cause the symptoms you can feel but not yet be bad enough to throw a CEL code.

My 99 would start, idle and drive slowly just fine. Any aggressive accleration caused a sputtering or missing of the engine. This continued as I checked other sensors and tried to trouble shoot. Finally the CEL came on and the code was for the coolant temp sensor. $35 later it runs perfectly.
 
Several things can act like or cause a bad O2 sensor. Burned valves, oil burning from bad valve steem leaks, heat gasket leak, silicone in coolant leaking in a head gasket will kill and O2 sensor, and carbon build up can affect them if it is running rich or burning oil. I doubt it needs PCM reflash, but how long did the new O2 sensor run OK, miles???
ve you had a code scanner check run yet?

A bad O2 sensor runs the engine rich and can overheat and damage the Cat converter, which can break loose the internal cat material and choke off the exhaust. Symptom is a rattle in the cat converter, exhaust.

Not all O2 sensor failures are detected by OBD-II

Injector #3 problem is a NO-restart of a hot engine problem due to heat soak.
 
well, i have replaced the tps, cps, cts, and o2 sensor. the engine does have alot of miles on it, and it is the original one for the truck. the week before our trip, i also replaced the spark plugs with autolites. when i go to work in the morning, when it is cold, it drives fine. it sits all day @ work, then when i go to leave, it idles fine and then when its in 2nd gear, it stumbles and pops until i goose the throttle or let completely off, then its fine. it did the same thing before i replaced the o2 sensor. also, yesterday, i was in blairsville for a funeral, went to leave, and it was stumbling @ idle and it kept doing it until i started down the road. i'm clueless on what the hell is wrong. if it had a carburetor, i'd have the damn thing fixed by now.
 
moparjim1987 said:
i think i might try a mopar replacment o2 sensor, if it fixes it then it was a faulty sensor. i'm running out of options and ideas.

Pull the spark plugs and check them first to see if any of them are carbon or oil fouled, if they are, then fix that problem first, before you bother with a 2nd O2 sensor.

Also from your description it might be a solenoid or solenoid wiring problem on the Transmission. The transmission is electrically shifted via 2 solenoids by a TCU computer.
 
I would still inspect the spark plugs, they can tell you a lot after only 100 miles, even on a engine that seems to run fine. Oil or carbon deposits can get on the O2 sensor if they are heavy enough and throw it off for a while. Also silicates from a coolant leak, internal or external are death to O2 sensor active elements.

What did the old plugs look like?

Do you have a color - texture chart for used spark plug tip reading. There is specific look for coolant leaks, for burning oil, running rich (dark black with excess carbon in just 100 miles) one for too hot and too lean....

Also a vacuum leak, or cracked exhaust (common on 4.0s!!!) will throw off the O2 sensor, making it think the engine is lean, and thus throwing it rich, which would explain the poor gas mileage with a good O2 sensor. Or loose manifold bolts which is common too on 4.0s, or a bad manifold gasket will also fool the O2 sensor wasting gas by making it think it is running lean.

I am doing a head job right now on one I bought recently, and the manifold gasket was leaking from loose screws, and the manifold was cracked too, with no outward signs of either problem. Your hick up maybe unrelated to the poor gas mileage.

Have you looked into the torque converter lock up issue?
 
my fiancee took the jeep today and she said that she didn't notice when it did, but the check engine light came on so i'm going to have to hook up the scanner to see what the hell is going on. we are finally getting rid of her cavalier so she will end up getting this xj so i want to get this fixed for her. i am buying a 91 xj and it needs a little tlc, but it is overall mainly solid.
 
i have replaced the oxygen sensor since my last post, and when i went to install it i removed the positive battery terminal to let the computer reset. after i reassembled everything, when i started it, it stumbled at idle like it did before, and today i cleared the code that popped up, which was the primary o2 sensor heater failure, it started acting up again. can someone relate to my problem? im starting to concider changing it to carburetor......
 
moparjim1987 said:
i have replaced the oxygen sensor since my last post, and when i went to install it i removed the positive battery terminal to let the computer reset. after i reassembled everything, when i started it, it stumbled at idle like it did before, and today i cleared the code that popped up, which was the primary o2 sensor heater failure, it started acting up again. can someone relate to my problem? im starting to concider changing it to carburetor......

Electricaly disconnect the pre-cat, front oxygen sensors(s), both (?) if you have two of them. Then start and drive it. IF all the problems go away, it is a problem in the O2 heater wiring or O2 heater relay. The ECU/PCM trips a relay that supplies 12-14 volts to the O2 internal heaters. O2 sensors need a working internal heater to give out good data to the ECU / PCM.

Typically when the ECU/PCM identifies a problem with an O2 sensor, it throws a CEL light and code, and then ignors the O2 sensor, and runs the engine rich, which if all else is working eliminates the rough running, miss, skip...etc. When you cleared the code the ECU/PCM went back to trying to use the bad O2 sensor data, which can make it act up and run badly at idle or cruise or light acceleration. The ECU/PCM ignors the O2 sensor data at WOT!

If you are lucky it is just a wiring problem or bad O2 heater relay or blown fuse if there is one.

I don't have the 97 FSM, drawings or layouts so I can't tell you where that O2 heater heater relay is, but is there somewhere. Your last code said the O2 heater is not getting power through that line
 
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