P0203 Code

[dido1055]

2006 Jeep Liberty 3.7v6
175k miles

So we swapped engine from an 07. Started right up, was driven a couple of times then O2 sensor was fixed. Changed all 4 sensors and now having P0203 and P0303 codes.

Accelerate to 2k rpm and hits sort of a rev limiter.

Have browsed through the forums but haven't got a definite answer.

Can the O2 sensor cause a misfire.?

We have swapped injectors, changed coils, spark are new. Pcm has been checked and came back with no faults.

Help!!

 

[Ksat]

P0203 means there's a problem with injector (or its wiring) @ cyl #3 and P0303 means a misfire has been detected at that same cylinder.

To answer your question, yes, a bad (upstream) O2 can cause a misfire, but in your case it looks like an issue with injector 3 is your problem

 

[mrlavalamp]

compression/leakdown checks?
Are you using the NGK copper plugs? Mine (and others on here) did not like the iridium plugs I tried, misfired quite a bit, but not just 1 cylinder.

If you are using the proper plugs, and have swapped the injector and coil, but the codes remain the same, I would think you are dealing with sealing issues or maybe something deeper in the wiring(like the harness/connectors).