Stutters and backfires - clogged cats?

[RockGlock86]

So the truck had been running fine after the plug wires being replaced, and whatever in the exhaust blowing out. Then yesterday is started backfiring hard again. It happened so fast, but I do believe I hit a bump in the road and it stuttered immediately, like something may have shifted in the cat, but I'm not 100% sure. I was about 4.5 miles from home, spun around and headed back, it did it intermittently on the way home, maybe 4 or 5 times, a few loud pops and then was fine then a few pops. It threw soft codes from the primary/secondary coils again, P0351/3/7, no number 5 tho. Never registered a misfire, or hard coded for anything.

I just removed the driver side upstream O2 sensor and ran it and it ran like crap for about 15 seconds then smoothed out and had intermittent popping about every 30 seconds or so usually 3 or 4 quick pops and they were much quieter than before. Yesterday my wife could hear me coming down the road from inside the house, today she didn't know the truck was running. After idling it for a couple minutes - long enough to pull codes and get a read on things - i turned it off and got underneath and the passenger side cat was too hot to touch, driver side cat was a little warmer than ambient, but not hot, id barely call it warm. I have a hard time believing that whole bank freely exhausted out the o2 hole.

So is this confirmation of a clogged cat?

 

[OR VietVet]

The best confirmation of bad cat(s) is typically a large variance of temps side to side or front to rear of each cat but I am a big fan of a back pressure test being done at a qualified shop. What are the miles on these cats and how old was the plugs and wires when changed?

 

[Rocket Man]

It’s a good indicator, which makes it worth paying for a flow test or back pressure test. That’s the only way to know for sure other than replacing. The other way to look at it is the mileage on the cats if you know that. They’re usually good for 125-150k in my experience so if they are close to that, you might just figure it’s time to replace them as a maintenance item. And don’t do just one, do both if you’re replacing.

 

[RockGlock86]

I bought the truck with 118k, its currently at 156k. I didn't change the plugs until a month ago, and the wires were done a week ago. The plugs that came out were autolites and the wires were duralast brand. Both were replaced with delcos for the time being I didn't want to throw expensive parts at it till I figured out what was going on. Given the mileage I'm assuming the cats are original, but I dont know for sure.

My guess is the cat is clogged, given the temp difference side to side, front to back, the mileage. Once I get the new cats on I will update and hopefully that fixes it. Im going to do o2 sensors aswell given the unknown history of everything and it will rule out that possibility aswell.

 

[OR VietVet]

It’s a good indicator, which makes it worth paying for a flow test or back pressure test. That’s the only way to know for sure other than replacing. The other way to look at it is the mileage on the cats if you know that. They’re usually good for 125-150k in my experience so if they are close to that, you might just figure it’s time to replace them as a maintenance item. And don’t do just one, do both if you’re replacing.

What Rocket Man said plus, do the oxygen sensors at the same time if they are the same age.

Sorry, I posted this and your post popped up just before mine. Good call on the sensors at same time.

 

[Rocket Man]

I bought the truck with 118k, its currently at 156k. I didn't change the plugs until a month ago, and the wires were done a week ago. The plugs that came out were autolites and the wires were duralast brand. Both were replaced with delcos for the time being I didn't want to throw expensive parts at it till I figured out what was going on. Given the mileage I'm assuming the cats are original, but I dont know for sure.

My guess is the cat is clogged, given the temp difference side to side, front to back, the mileage. Once I get the new cats on I will update and hopefully that fixes it. Im going to do o2 sensors aswell given the unknown history of everything and it will rule out that possibility aswell.

Sounds good. The last set of cats that plugged up on me had about 150k on them. One side was 60% restricted, the other 20% and they caused all sorts of troubles and codes for misfires, O2 sensors, MAF sensor and would go into limp mode. And I agree on the O2 sensors. Looking forward to the update, hope this takes care of it.

 

[RockGlock86]

I hope this takes care of it all too, After this it will have new cats, o2 sensors, plugs, wires, cam, lifters, and every sensor I came across in between, new dual batts, I just did front wheel bearings a month ago, and about a year ago it got upper and lower ball joints, man I should have just bought a new one....

I appreciate all the feedback guys it really gives me motivation that I'm fighting in the right direction.

 

[79jasper]

What was the result of the fuel pressure test?

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[RockGlock86]

key on/engine off 55

 

[79jasper]

What about running and WOT?
I only ask because I had two trucks at work that had failing fuel pumps, in turn wiped out the cats.

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