O2 Sensor Lean/Rich Question

[Maverick6587]

This is more of a vent than a question I guess...

I think the car has had a knock for about a month. It's my stepdaughter's car and I just have not had any time to look into it at all. I'm still finishing resolving my 97x's issues. We bought an extended powertrain warranty on my stepdaughter's car, a 2004 Mazda 6. There was nothing wrong with the car when we bought it from the stealership.

The car had been running rough for a few weeks and nothing bad enough to warrant immediate attention. A few spirts of what sounded like a misfire/rough idle. I test drove it but, did not hear/feel any misfires.

One day the car would not start in the parking lot at her work. I was still at work and towing was covered by AAA. So, we had it towed to the dealer for troubleshooting, since we knew it had a warranty for the drivetrain. It ended up being a dead battery. Since it was covered by the extended warranty we had them inspect the vehicle since it was covered.

They said they found a P-304, no other codes were mentioned in the report. My GF/Fiance had told them that the CAT was bad. The mechanic proceeded to tell her that because of the misfire of ONE cylinder. There was extra fuel passing by the O2 sensor (that hadn't been burnt) and was the bad CAT code, that I have never even seen and don't know who told either of the girls, that it was an issue.

Am I right to assume that IF extra fuel was passing by the upstream O2 sensor, a lean/rich (I assume lean) condition would have been seen by the upstream O2 sensor? And possibly then the bad CAT code given by the downstream O2?

The only codes that were written down in the report of the mechanic were P-0304, misfire on cylinder 4. When I scanned it the day it got back from the stealership. I had ONLY two codes, P0022 ("A" Camshaft Position - Timing Over-Retarded Bank 2) and P2092 ("A" Camshaft Position Sensor Acuator Control Low Bank 2). The codes were not cleared but I did not see after 5 or 6 restarts any misfires.

I "assume" that I should have seen two different codes IF that mechanic was correct in his assumptions, one for the misfire and another for lean/rich O2?
me"

 

[Mooseman]

I can't remember a rich code due to a misfire. Quite possible the PCM is programmed to not report a rich condition due to a misfire, which would be a logical reason for being rich. Actually more than rich, it's raw unburnt fuel.

The cat might not be bad. Depends on how long it was running with the misfire. Fix the misfire and check it for backpressure.

So it looks like it may also have issues with the VVT. They may have unplugged the CPAS for a while and didn't clear it? If any of those codes come back, check or replace the CPAS as well as its wiring. Also pull and clean the cam sensor. The CPAS is a high failure rate item so I'd just replace it to eliminate it as a source of the codes.

 

[gmcman]

Your P0304 code was likely set because the hood seal has a drip opening right above the #4 coil pack, which causes it to fail early. You can swap that coil with another and see if it follows but good bet it's just a coil.

Also, I did this recently and would never have thought it would make a difference, but after I had a coil go bad, I replaced the bad coil and drove it for a few days. Then I replaced all 6 for less than $80, (keeping the one newer coil as a spare) and the engine had a noticeable difference in responsiveness. If the coils are all old, I would replace all of them.

As far as your camshaft code, unplug the CPAS connector and look for oil in the CPAS connector. If you have oil it needs to be replaced.

What oil are you using and the oil change intervals?

 

[budwich]

Potentially the "assume" part is not so good. The "rich / lean" codes only show up IF in the system's attempt to compensate the mixtures, the upper / lower limits of the trim adjustments are exceeded for a "period of time". If you monitor your fuel trims, you should notice where they are, at normal idle and at "running speeds". It is possible that the misfire of a single cylinder might not been severe enough to push others codes.

As for the "bad cat", the suggestion for checking for back pressure is good. You can also try monitoring post cat O2 sensor to see what its response looks like. It will likely tell you something is up. IF the cat is bad, there should be other signs, such as bad power response to acceleration and even just poor general power.

I guess my question of the "vent" is this is for a mazda right? how is that tied to a trailblazer other than having multiple vehicles with issues... :-(

 

[gmcman]

I guess my question of the "vent" is this is for a mazda right? how is that tied to a trailblazer other than having multiple vehicles with issues

I was thinking the same, not sure which vehicle but I spoke of the TB.

 

[Maverick6587]

Thanks for all of the responses!
I'm going to go for the active codes for now. I'll replace the CPAS first and see what happens, it's a cheap part anyway.

I'm hesitant on the VVT solenoid only because the solenoid is sold with a guide, which looks like a timing chain guide. I'll have to do some more research though.

After I change the CPAS, I'll troubleshoot cylinder 4, by swapping spark plugs and then swapping ignition coils.