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too much flow through catalytic convertor?

B

bassfishinXJ

NAXJA Forum User
Location
Missoula, MT
I have a 98 xj with 4.0L I have put a bank torque tube on it and a high flow cat, new O2 sensors and muffler. check engine light is on. is it possible that my new cat has too much flow causing the codes for O2 sensor failure? i have re replaced the sensors with no change. hesitation, miss-fire, bad milage. i've tripple checked header bolts wnd can find no exhaust leaks. any ideas? i looked through some older threads but didnt find any info that really helped
 
ive had the codes checked a couple of times.. just cant find the paper they are written on. they have been for the O2 sensors. TPS is only two years old, I thought about Idle air sensor but itll miss fire at any RPM not just idle/off-idle. it actually seems like the timing is off but sense that is PCM controlled not much i can do there. my last xj ran like ass till i changed the O@ sensor... like a dream after that
 
i have pretty close to the same problem...with a 98, put in the header and high flow cat to accompany the intake and exhaust system and about a week later it began to stumble. ive checked everything from vaccum/fuel pressure, to clogged cat, replaced o2 sensors. maybe too much air flow with not enough fuel/spark? im going to test my MAP, IAC and TPS and if those are fine i may start thinking about some new plugs. shouldn't need higher rate injectors for what we've done...lol the header isnt THAT good :S
anyway, for our sake i hope this gets figured out
 
If your high flow converter isn't doing a good enough job of cleaning up the exhaust than the rear o2 sensor will set the light off. I bet your stock cat shuts the light back off (after you clear the code) and probably won't cost you many HP if any. But if your hellbent on keeping your new cat - If you look around you can find plug in "MIL" (malfunction indicator lamp = check engine) elimimators. They plug into your rear o2 sensor connector and give the computer a "clean" signal. Thats all the rear o2's really do - monitor your cat(s). Check late model mustang stores or sites, they'll have em. Off road use only of course.;)
 
oh i dont care ive already switched it out and tried it with the stock cat, and found no difference, so..not sure that it is his problem either... but either way i dont really care about the idiot light, as you say its not having any effect on the engine anyways..altough thats if you are sure its coming from the rear o2... its the hesitation and stumbling that tends to get on my nerves... lol but i could just be speaking for myself..
 
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ohhhh... I thought you meant you had NO stumble, hesitation etc.. Ooops.

Running too lean? What did the codes say? It could be seeing a too lean condition and the ecm is too far out of its "window" of adjustment - throwing a o2 too lean code.
 
You gotta love the OBD2--helpful for diagnosing problems but sometimes doesn't like performance upgrades(like when I tried to use the Hypertech programmer). I would disconnect the battery and let your computer relearn, if you haven't already.
 
i have run tests on it with a mopar computer from my buddies work. at the time it said either i had a fuel leak in # 3 or 4 cylinder or needed a PCM. we couldnt verify if there was a fuel leak or not. put a new PCM in it.... did the exact same thing within minutes of start-up. the computer indicated both O2 sensor were functioning but every few minutes something would change and it will lean itself as far as poss. then return to normal. few min later rich itself and return to normal. every time it hit the extremes it would miss fire and stumble like crazy, just before it sounded like it would die rpms up to 2500 and then slowly lower to idle. we couldnt fig it out
 
Before I went any further I would Double and Triple check ALL your grounds, Remove, Clean reinstall all the straps / cables etc. Then I would unplug all sensors one at a time, verify the plugs are in good shape and plug back in... All with the Neg batt. cable off, then try it all again. Bad grounds can lead to Lots of Odd problems. ~Ace~
 
CPS? I have a 62mm TB with 2.5" exhaust from the APN header back into a Magnaflow cat and Ravin' muffler with 2- O2 sensors and no problems.
Reason i suggest a Crank Position Sensor is mine had a wire loose at the plug of the CPS, which i could not see visually until it was pulled and checked. The wire would touch and things would be fine, then hit a bump and stutter, no-starts, etc and threw codes as o2. HTH -B
 
i hadnt checked the CPS yet. ill hyave to get on that in the am, i havnt had a problem with no-starts but its def worth the look. the gremlins have definately invaded my XJ. now that its warming up the mis-fires are getting more frequent, and hesitating alot until it mis-fires then bang it takes off
 
no honestly still cant find the gremlin. grounds are good, cps and wiring are good. still acts like it doesnt have an o2 sensor. gonna have to check the wiring there again. more hesistation now with 80 degrees out and engine temp ~210-220
 
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