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I have a 98 TJ 4.0 Sport- 92000 miles. after about 2-4 minutes of operation, it starts to kick back throught the breather, pop and loose power for around 4-5 seconds. once it does this, it runs fine. it usually does this when you first start driving. i have replaced wires, plugs, distributor cap and buttum. plus replaced throttle positioning sensor, fuel sending unit and had it put on the diognostic machine twice. even the dealers are clueless. i see that there is a "upstream" and "downstream" O2 sensor, but what does this mean, where is it and will this help. i also just had the catillitic converter removed...same problems. what do i do now?
 

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Phill, welcome,

If you have CA emmsions you have 4 O2 sensors if not you have 2. One should be either just forward of the cat or behind it. THe other should near the pre-cat, at least I think that is what they are called,, looks like a big coke bottle below the manifold.

Did you check the fuel pump or fuel filter, as well as there connections. TJ's are known to have issue's with the wire pack at the fuel tank working their way out. Keep us posted on this.
 

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The upstream 02 sensor constantly monitors the air-fuel mixture and the downstream 02 sensor makes sure the catalytic converter is working properly. When the upstream sensor goes bad, it causes poor performance and a dramatic loss of fuel economy. Nothing really happens performance-wise if the downstream 02 sensor goes bad. Either going bad will cause the Check Engine light to illuminate.

Have you had anyone read your engine's diagnostic codes? You might be able to read your own codes with the following procedure but understand that this ability was removed in late-model 1998 TJs and did not reappear until sometime after 2000.

Try this and see if you can get your engine to display any stored diagnostic codes... without starting the engine, turn the ignition key on-off-on three times within five seconds and after leaving the key in the 'on' position, wait. It can take 5-10 seconds so be patient at this stage. If the codes are going to display, they will start appearing in the odometer, together with the Check Engine light blinking as the codes appear. If it works, you will always at least get a '55' code which doesn't indicate anything except that it worked.

I'm thinking maybe a bad crankshaft position sensor but it's hard to tell at this point. :)
 

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Thanks for your reply, were is the upstream 02 sensor located? and the downstream and if the catalytic converter isn't on the jeep anymore will this matter ?:confused:
 

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The upstream sensor should be just below the exhaust manifold. The downstream sensor is screwed into a bung on the catalytic converter.
 

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How long have you been driving it without the CAT? I am just curious as this may be the problem, or if you just need a good cleaning on your throttle body. How long has it been running like this?
 
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