Like stated above. It your truck is having problems with cats there's an issue up wind. The cats going bad are a symptom of an issue.

 

My cats are toast, at least my passenger one. Had a stuck open injector a year ago and it flashes a code for the cat being below efficiency every once in a while. I'm either going to gut them or cut them and disable the rear o2 sensors.

 

Hmmm well, like I've said, I never had another CEL other than those 2 come on. I always use top tier gas, maintain the truck religiously, the truck is 100% stock, and I don't beat on it. I didn't get a chance to replace the plugs and boots this weekend due to other priorities, but next week, Ill pull them out and check them to see for any richness. BTW the #3 plug that I did replace during the trip shows absolutely no issues on it whatsoever. No dark carbon, no brown from oil burning, gap was in spec. So I'm seriously doubting that it was missing before the trip...

 

As I noted earlier, you can have an intermittent miss that does not trigger a CEL but is enough to effect the cat on a long term basis.

Make no doubt, the cat did not fail on it's own and the fact that you got a code for a #3 issue after is proof of that.

Hopefully the boots and springs get you in check. I would suggest a trip to someone with a quality scan tool to check for any misses after you get the work done to be certain.

 

Will do. Hopefully no more misses on that cylinder since it now has a brand new Denso coil and MC 509 plug in there.

 

Changed all 8 plugs this weekend along with boots. All looked perfectly fine. No dark carbon or signs of oil burning, running rich or lean....I have no idea what could have caused the miss other than a possible defective cat. The old plugs looked almost like ones that have been in service for 20-30k. Same with the boots. I know for a fact these are at least ~45k old, since I bought the truck used. Any ideas? Didnt get to grab a pic since my phone was dead...

 

Interesting. I beat on mine, floor it often, run 91 octane in it with my Gryphon settings having the timing advanced 1.5 degrees. 157K now and no issues. You sure all your injectors on that bank are good?

 

A bad cat will not cause a miss. There is no way for that to happen.

It's not like the old days where you could just read the plugs and know what is going on. An intermittent miss, one not often enough to trigger a code, can and will eventually take out a cat and may not leave evidence on the spark plug.

This is why expert diagnosis is so important today. The old school methods do not apply well today. We have pushed efficiency so much higher now that problems are no longer obvious and must be diagnosed through a detailed view of engine operations. Typically when you can see the issue visibly, it has been ongoing for a long period of time and at a very high level of inefficient operation.

 

@650NutKase, thought I had seen where you were a Torque Pro user, but can't find it again - just mentions of codes. But if you have a code reader with graphing capability, or logging that can be exported to MS EXCEL, it is not hard to resolve the defective CAT possibility. I graph O2 sensor 1 and O2 sensor 2 on both banks on one screen - which should look like this: ................



--Pre and Post CAT sensors

If the Post-CAT Sensor 'tracks' the Pre-CAT sensor, its BAD. "Some switching on #2 is going to happen and is tolerable (under load or Open Loop operating condition). But, the efficiency codes result from exceeding factory spec. "RATIO" between voltage switches between Pre-CAT and Post-CAT sensors.

There is a 'treasure trove' of information in your PCM about misfires. If you have Torque Pro, I can provide you the OBDII Parameter IDs and formulas to the dashboard shown below that I have put together to monitor misfire 'stuff'.



The PCM sets a Misfire flag when misfiring (the condition that flashes the CEL) You can set up a Torque 'Alarm' for this flag becoming 'non-zero'. It even counts number of 'drive cycles' _SINCE_ the last misfire. (Mine is at 57). When a misfire occurs, MFTot count is incremented, and a snapshot is taken of seven different conditions at that instant. Pretty useful.






OBDII Misfire flags, statistics and freeze frame data

 

Dirt,

This is what I was thinking. The cat tears itself apart due to defect. The debris clogs the rear of the cat when accelerating, this causing a ton of back pressure in the passenger bank, thus resulting in a miss fire? Thoughts?

Torqued,

I have the free version of Torque on my phone (which is now bricked...). Once I get my replacement, I'll do a data log. I thought I read that the free version can do mode 6 logging. Am I correct? I had no pending (unverified) codes logged on the PCM during the failure.

Thanks guys!! I'm just so stumped on how this happened....