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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[RockGlock86]

Update.
So Got the Y pipe and got busy with life. When I removed the bank 1 upstream it had been cross threaded in and hard at that. Tried to remove the Y pipe and snapped the first two bolts on the driver side flange, figured at this rate I might as well take it to the local exhaust shop. Good guys, do good work. On the way there, with 2 broken bolts on the driver side and no upstream sensor it sounded like my harley. The shop owner hears it and runs codes and it has a slew of random codes from cat/o2 sensor/coolant sensor/ coils/misfires/oil sensor and he swears it is a bad ecu.

Back pressure test and no reading from the driver side cat, passenger cat has 7 psi of back pressure, not sure how that reads as a % constriction. Remove the y pipe, which the factory pipe is actually a really nice all stainless unit, and the driver side cat is empty. Completely empty I wouldn't have believed it if I hadn't seen it. The brick in the passenger side has shifted aswell. Replace the Y pipe, all 4 o2 sensors with Denso's and clear codes and it runs fine. No codes, no hiccups, idles smooth and full power. Still a couple little tings of loose metal int he exhaust but other than that its all good.

Now, continuing issues. the cat temps are still 100 degrees cooler on the driver side in town driving. under hard acceleration I saw 1550 on the passenger cat and 1375 on driver side. So still a temp variation, with new plugs and wires, and coils have been mixed between banks, new intake gaskets, pcv valve and line. I can and probably will replace the coils just for GP, I cant think of anything else on why the driver bank would be cooler. Except for injectors. I assume that injectors are originals.

Does anyone know what fuel trims should look like or how can I get a read if the driver bank may have a dead or dieing injector or somehow is fueling less than the passenger bank?

 

[swathdiver]

Update.
So Got the Y pipe and got busy with life. When I removed the bank 1 upstream it had been cross threaded in and hard at that. Tried to remove the Y pipe and snapped the first two bolts on the driver side flange, figured at this rate I might as well take it to the local exhaust shop. Good guys, do good work. On the way there, with 2 broken bolts on the driver side and no upstream sensor it sounded like my harley. The shop owner hears it and runs codes and it has a slew of random codes from cat/o2 sensor/coolant sensor/ coils/misfires/oil sensor and he swears it is a bad ecu.

Back pressure test and no reading from the driver side cat, passenger cat has 7 psi of back pressure, not sure how that reads as a % constriction. Remove the y pipe, which the factory pipe is actually a really nice all stainless unit, and the driver side cat is empty. Completely empty I wouldn't have believed it if I hadn't seen it. The brick in the passenger side has shifted aswell. Replace the Y pipe, all 4 o2 sensors with Denso's and clear codes and it runs fine. No codes, no hiccups, idles smooth and full power. Still a couple little tings of loose metal int he exhaust but other than that its all good.

Now, continuing issues. the cat temps are still 100 degrees cooler on the driver side in town driving. under hard acceleration I saw 1550 on the passenger cat and 1375 on driver side. So still a temp variation, with new plugs and wires, and coils have been mixed between banks, new intake gaskets, pcv valve and line. I can and probably will replace the coils just for GP, I cant think of anything else on why the driver bank would be cooler. Except for injectors. I assume that injectors are originals.

Does anyone know what fuel trims should look like or how can I get a read if the driver bank may have a dead or dieing injector or somehow is fueling less than the passenger bank?

Yeah, fuel trims should be around zero once your running at a constant speed for a bit. At idle they should be near zero too. If there's some kind of vacuum leak, they'll be in the negative and over 10 (-10s).

A Tech-2 or bi-directional scan tool can turn off the injectors and run tests on them and the coils and such.

 

[RockGlock86]

I have a OBD2 reader and the torque pro app right now. so FT 1 and 2 are in constant fluctuation, there is no steady number reading. bank 1 floats in -0.5 to -1.5 at idle and bank 2 is -2.5 to -3.5 at idle but at times they will zero but its for a second and then back and forth, under high idle 1500 rpm they will both be -2.0 to -3.5 and if I rev it to 5k and let off it will give high + numbers, +5.0 to +7.5 on bank 1 and +4.0 to +6.5 on bank 2. These numbers are all in park, no load.

While driving they are generally the same but on the lower end of the ranges listed above. Also does new cats have a new cat smell? it doesnt smell like standard exhaust, I can't put my finger on it but its just off. Also idling in the drive way I get these random wisps of exhaust every 45 seconds to a minute. Visible exhaust as if it were a cold morning. I have driven a total of about 30 miles so far on the new cats and o2 sensors.

 

[Rocket Man]

Not sure about the fuel trims, James knows more about that but that smell and a bit of smoke is normal for the first few hundred miles.

 

[RockGlock86]

Not sure about the fuel trims, James knows more about that but that smell and a bit of smoke is normal for the first few hundred miles.

That's good, I was immediately concerned I either got bad cats or something else was wrong

 

[RockGlock86]

So its back at it. I get in the truck this afternoon and it doesn't start, it didn't do anything. I turned the key to on at first and let it go through the cycle, just a force of habit is all, and then I turn to start and everything goes off. No clicking, just all off. I turn the key back off and then back to accessory and it cycles through fine, and then to run and it looses power again but i held the key there and after 2-3 seconds, it powers up and starts. Everything seems normal, except for the oil minder is reset to 100 and the engine hours is reset to 0.

I drive normally about 2 miles and then I loose power almost like a limp mode, slight backfireish sounds but very quiet, like a **** or a bump noise. I pull over, turn the truck off and then restart and it cranks a little longer than normal, but not overly long, and fires up still in this limp mode. I do not know if it is an actual "limp mode" I just do not have full engine power. Roll the 2 miles back home as its mostly down hill anyways, pull codes, I have a 303/351/353/357. So not even sure where to go from here. Obviously the cats were toast, but that may have been an effect and not a cause.

Through all of this its always on the driver side bank, the cat temp issues, the coil codes and the misfires. I think its almost electronic maybe and not some sort of mechanical issue. I have switched the coil packs previously as a set from bank to bank and it still only threw the codes on driver side.

 

[Rocket Man]

I’m wondering if you have a cracked intake manifold. I know in your first post you said you broke the plastic on the intake manifold GASKET. Explain this, and also what did you torque the manifold to? You wouldn’t have been the first to torque to ft/lbs instead of in/lbs if that happened. If all your misfires are on one side and the cats weren’t the cause but instead a symptom, it seems like it’s more likely an issue with something that happened on that side of the motor when you were doing the AFM delete.

 

[RockGlock86]

I did torque to in-lbs, and followed the torque specs and pattern shown on the jegs website.

I did break the plastic gasket, both of them actually, but I very well could have broken the manifold too. It could be cracked near the driver side cathedrals and be the reason why it's only affecting that bank? I'm not sure what else intake manifold related could have caused all this, but it definitely started after I had the intake off the last time. I had a couple hundred miles on the AFM delete and non such issues and then pulled the intake to replace the gaskets and it started 2 miles later. I guess from here I can pull the intake again and really clean and inspect it and see what I come up with.

 

[Rocket Man]

I did torque to in-lbs, and followed the torque specs and pattern shown on the jegs website.

I did break the plastic gasket, both of them actually, but I very well could have broken the manifold too. It could be cracked near the driver side cathedrals and be the reason why it's only affecting that bank? I'm not sure what else intake manifold related could have caused all this, but it definitely started after I had the intake off the last time. I had a couple hundred miles on the AFM delete and non such issues and then pulled the intake to replace the gaskets and it started 2 miles later. I guess from here I can pull the intake again and really clean and inspect it and see what I come up with.

I have heard cracks in them can be hard to see. Might be worthwhile to just replace it, idk.

 

[RockGlock86]

I have heard cracks in them can be hard to see. Might be worthwhile to just replace it, idk.

Real world is this something that can be yarded or is it best bought new? Should I get other new stuff with it or just the plastic manifold and switch everything over with it?