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Ok this will be a long one.

2000 model 4.0 5spd non California emissions
It started with an injector, and misfire on cyl4 code. Being that the odometer shows 221k miles I ordered a full set of oem injectors from amazon. It turned out that the oem injectors were the four port instead of single port. Put them in and all seemed good for a bit. Then I started getting CEL P0172 (system rich bank 1).

Knowing the oxygen sensor is rarely truly the culprit I started with the basics chasing troubles.

First plugs, the old plugs were in terrible shape which led me to believe the previous owner didn't know what the word maintenance meant. So I put in new plugs gapped properly. Unfortunately the parts store was out of copper plugs so I did step up to a slightly "better" grade. I know that can be questionable with 4.0s, but it was my onlycoption at the time.

Coil rail, I checked the coil rail while doing the plugs. No arcing or sparking and the rubber looked good. So I left it as it was.

Sensors

Replaced the map and tps sensors. Pulled the throttle body and idol air control valve. I cleaned all to factory new condition and checked the to see that the iac was moving and quickly, it was. I also pulled the iac housing off the side of the th and cleaned it to facotryvnew shine. (Do not remove the housing unless completely nessicary as the gasket for it to is not available anywhere I could find. I had to cut a new one from gasket material). Also replaced the tb gasket when going back together.

I replaced a couple vacume elbows that the rubber had gotten hard on. I checked for induction leaks and haven't found anything else.

I did go on and replace the oxygen sensor, the old one wasn't pristine, but I have seen plenty worse.

I have also run a can or 2 of seafoam through the last couple tanks of fuel.

So here I am she will go a 1/2 to a day before tripping the code again.

I'm at a loss unless there is a clog of some sort in the exhaust. How can I tell if there is a clog in the cat or muffler?

Any other ideas?
 
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