99 with a 2.5 has started to misfire typically around 3k rpm. It is intermittent and only after the engine is up to temp. It bucks, stalls and the CEL flickers but does not stay on. No codes. I replaced plugs and wires yesterday, no improvement. When I disconnect the upstream O2 it doesn’t seem to miss as often but doesnt go away entirely. The CEL does come on with O2 disconnected but shuts back off when it misses. Replaced O2 last year but not sure on manufacturer. Any ideas? Appreciate the help.
Engine misfire
- Thread starter Kit1331
- Start date
Left out the fact I replaced the intake manifold a couple weeks ago which fixed a size able vac leak. Brought idle from 1100 down to around 750. Double checked all the connection and wire harnesses. Drove fine up until now. No sure if related.
Start with the O2 sensors and wiring. Many have seen weird issues with anything but NTK/NGK sensors.
https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/
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That the miss only happens once the engine has warmed up right away makes me think the upstream O2 sensor has gone bad. The PCM starts referring to the upstream O2 sensor for setting the air/fuel mixture once the engine has started to warm up.
If you replace it, make sure to only use an NTK or NGK sensor, avoid Bosch and store brands. No need to replace the downstream O2 sensor on the catalytic converter, it has nothing to do with how the engine runs... it only monitors the cat.
If you replace it, make sure to only use an NTK or NGK sensor, avoid Bosch and store brands. No need to replace the downstream O2 sensor on the catalytic converter, it has nothing to do with how the engine runs... it only monitors the cat.
Well here goes my misfire mystery. 99 with a 2.5L. Misses around 3k rpm mostly in 3rd gear but also in 4th occasionally (havent figured out what 5th gear’s good for yet). I’m currently throwing parts at the dang thing. Every part I’ve put on it has been mopar or replacement brands recommend by you guys. Thanks for all the help!
Plugs/wires
Upstream O2
Crank sensor
Tps
IAC (previous issue)
Cap and rotor
Sure Im forgetting something.
Where it gets tricky is it will not code. CEL flashes during the miss but does not stay on. Reader loses link during the miss as well. Ever time Ive replaced something it seems to have fixed the problem for a few days, then it progressively returns and gets worse in no time. Battery disconnected during each part throw maybe the reset is causing this. I currently have the O2 sensor disconnected and again it ran good w/o it but of course turned on the CEL. After a few days it started missing again and no longer has a code for the missing O2 sensor. Im lost. Any advice would be great. Thanks
Plugs/wires
Upstream O2
Crank sensor
Tps
IAC (previous issue)
Cap and rotor
Sure Im forgetting something.
Where it gets tricky is it will not code. CEL flashes during the miss but does not stay on. Reader loses link during the miss as well. Ever time Ive replaced something it seems to have fixed the problem for a few days, then it progressively returns and gets worse in no time. Battery disconnected during each part throw maybe the reset is causing this. I currently have the O2 sensor disconnected and again it ran good w/o it but of course turned on the CEL. After a few days it started missing again and no longer has a code for the missing O2 sensor. Im lost. Any advice would be great. Thanks