Stutters and backfires - clogged cats?

[RockGlock86]

So I recently replaced 4 lifters after replacing all lifters with AFM delete. All was well for a few days. Yesterday I got a bank 1 lean code and after looking I had a big crack in the rubber boot for the pcv hose where the hard line meets the valve cover. When I had the head off last week I cracked the plastic on the bank 1 intake manifold gasket aswell. I replaced the little rubber boot yesterday and got another lean code within 15 minutes. So assuming it was the intake manifold gasket, I pulled the intake off this morning, and put down Fel-pro metal gaskets instead of the plastic ones. That went normal. When I had the intake off it had oil dripping out of it, seeing as I had just cleaned it a few days ago when it was off the last time I figured it would be a great time to replace the driver side valve cover with the new style that is supposed to cut down on oil consumption. Replace valve cover, replace intake, hook it all back up and fires right up. Idles fine, revs fine. I leave and make it about 2 miles from my house fine and then it starts backfiring hard and stumbling. no power, wont really make it over 2k. I get a P0355 code, and limp back home. I switched the coils with No. 3 and fire it up and check codes and now I have P0353 and P0355, I cleared the codes in case of some ghost in the system, scan again and and now have P0351, P0353 and P0355. seeing as these are all driverside coils I switched the whole coil plate from side to side, thinking it would follow it. Run it clear faults and scan again and still all driver side faults. So I am thinking that either the large grey plug for the coil harness has malfunctioned or maybe there is something else I am missing?

 

[thompsoj22]

injector harness? are you sure it is ignition and not fuel related? although backfiring defines timing not necessarily no spark, no shop rags/paper towels left behind in the intake or head ports? if i read the post correctly, you initially replaced all lifters with AFM delete, than had to go back in and replace 4 of those? did you plug/cap the fuel rail during the R&R? If there were only 4 lifters replaced and they were on the drivers side i would guess lifter compatibility problem or debris in the valve port. ie valves staying open, this will backfire like a mother f'er do a compression test on the affected cyls and verify valves seated? im just guessing! hang in there!

 

[RockGlock86]

No shop rags left in or anything like that I double checked all that before reinstalling everythign and my wife held the wiring harness up while I slide it in place and set it down. I will go out and double check injector harness right now and see if thats all good, I guess I could have a couple injectors plugs switched maybe? could something like that cause this type of behavior? And yes on replacing all 16 lifters, and then going back and replacing 4 of them again. I had another thread about it, I think basically it was crap lifters from a budget kit. But it could have been something I did wrong too.

 

[89Suburban]

Sucks bro. Yep check, check and recheck. I found a few things wrong from installation when I had mine apart. Did you snug up the valley pan bolts? If you have oil coming out of the intake you need a catch can. Check the coil wiring harnesses real good, I nicked one and caught it when installing the intake.

 

[thompsoj22]

No shop rags left in or anything like that I double checked all that before reinstalling everythign and my wife held the wiring harness up while I slide it in place and set it down. I will go out and double check injector harness right now and see if thats all good, I guess I could have a couple injectors plugs switched maybe? could something like that cause this type of behavior? And yes on replacing all 16 lifters, and then going back and replacing 4 of them again. I had another thread about it, I think basically it was crap lifters from a budget kit. But it could have been something I did wrong too.

do a compression test on the effected cyl's and verify valves are sealing, the injector harness probably laid in place perfectly and im not sure that you could miswire one injector to the next? the fact that it started, idled and than drove for a couple miles til it fubar'ed basically rules out any connector mixup?

 

[RockGlock86]

I just checked all my injectors against the wiring diagram and everything is in place, its only the driver side that is effected no matter what parts I swap, and a couple times I have gotten an actual misfire code, P0301, but other than those one or two times it has been coil primary/secondary code, P0351/3/5. Never a P0357 though not sure if that matters. I checked all my connections and plugs and everything is in place. Something I just noticed, as I was laying under the truck while it was running, it sounds like there is one or maybe two small metal objects inside the exhaust where the banks come together. After the cats and before the muffler the Y there. Not sure if it is relevant either but my cats are 150-200 hotter on the passenger side vs the driver side, consistently. Also in laying under the truck I noticed the downstream driver side O2 sensor wire was rubbing against the front driveshaft and one of the browns in there had a rub through the jacket to the copper, only one wire tho. I just repaired that aswell.

 

[Foggy]

Just a thought: I wonder if your injectors themselves are bad OR your fuel
pump is weak... that will certainly cause a backfire AND that driver side Cat
to not heat up.. the pcm may be cutting spark due to no fuel... food for thought

 

[OR VietVet]

A compression test and fuel pressure test is needed to help eliminate the basics. How old are the plugs and what do they look like. The compression test should be done with all plugs removed.

 

[Fless]

A compression test and fuel pressure test is needed to help eliminate the basics. How old are the plugs and what do they look like. The compression test should be done with all plugs removed.

Does "all" include #8? It's sooo haaard! LOL

 

[OR VietVet]

That's a big WAAAAAAHHHHH!!! Suck it up.

 

[RockGlock86]

About a year ago, everything in tank was replaced, injectors though are unknown age. Plugs were done when the AFM delete was done so maybe 3 weeks ago now. Wires are unknown age, and one of them, No 7, isnt part of the set. I read on a different page that a dead cat could cause similar issues, with the temp difference and the metallic rattle sound it could have finally went.

So compression test, fuel pressure test. Take the Y off and shake it out

 

[thompsoj22]

"Is the electronic AFM delete" associated with your mechanical AFM delete known to be good? If the compression test is good,ie no valves hung open, Than i would guess somthing is fubar on the electronic disabler? It's gonna be somthing simple, tech2 and someone who know's how to use it would diagnose quickly. Compression test will rule out mechanical faults and that your backfire is not being caused by an open intake/exhaust valve on compression stroke.

 

[RockGlock86]

I got a new ECM/TCM from Black Bear with AFM delete and 89 tune for the summit cam. Its on its way to my buddys shop right now actually, he will do compression, fuel pressure, and all that. I dont have time to work on it right now and I need it up. As soon as I get info from him I will update. I hate threads where people have issues and never say how they were resolved.

 

[Geotrash]

My money is on a dead (plugged) cat. And the smoking gun is the mismatched ignition wire - probably replaced when it had a misfire that dumped enough unburned fuel down the exhaust to kill the cat. Please do follow up to let us know!

 

[Rocket Man]

You could pull the upstream O2 sensor on that side and start it up to check if the cat is plugged.

 

[RockGlock86]

You could pull the upstream O2 sensor on that side and start it up to check if the cat is plugged.

I have read about this, but what am I actually looking for? It running better after its unplugged or it will backfire out the O2 bung? I read another forum they told them to do the same thing pull the sensor and leave it plugged in, but never quantified what to observe.

 

[iamdub]

I have read about this, but what am I actually looking for? It running better after its unplugged or it will backfire out the O2 bung? I read another forum they told them to do the same thing pull the sensor and leave it plugged in, but never quantified what to observe.

If the cat is plugging up the exhaust, removing the sensor will create a hole for the exhaust to escape through, which would result in an improvement in operation.

I'm hoping it's just an electrical failure, but fearful of a failed head gasket or cracked head on that side.

...You did use a new head gasket and bolts when you opened it back up, right?


With it running fine then suddenly acting up a couple miles from home, either it's a failed sensor that was ignored until the PCM went into closed loop or something let go.

 

[RockGlock86]

Both times when I had it all torn down, and when I had the head off the second time I used new fel-pro head gaskets and bolts, the multi layer metal gaskets. The only gasket I ever reused on this motor was the intake manifold gaskets when the head was off the second time, as they had just been replaced, and regardless they were replaced anyways just a couple of days ago. I'm hoping it was a sensor too of some sort once it went into closed loop, or that atleast contributed to it. When the intake was off for the gaskets I unplugged the tb, whatever the sensor is on top of the intake, and the injectors, I had the driver side coil harness unplugged also to do the valve cover, and the batteries were disconnected before all of that and I had the alternator still mounted but unplugged to get the pos lead out of the way for the intake.

 

[OR VietVet]

What @Rocket Man and @iamdub said about the pulling the sensor to create a hole. The cat may not be completely plugged but could get worse after heating up when driving and then the problems occurs.

 

[RockGlock86]

Update.
So the No. 5 plug wire melted inside the cable, and somehow this was creating a ground fault that was shutting down all or most of the coils on the driver side. So when I moved the cable from 5 to 3 it stayed on the driver side and when I switched the coils back and forth it stayed on the driver side too.

If I had switched the plug wires from bank to bank I could have potentially identified the or narrowed down to the wire, but bank to bank never crossed my mind, I was stuck on the whole side being shut down. New set of plug wires and all is well again. Ran a cam relearn just for gp and she runs like a champ again. The only connection this can have to the previous work I did that I can think of is somehow in removing the coils when I removed the valve covers, I damaged that plug to wire connection. I never disconnected the wires from the plug until I had the backfire and moved them between the cylinders.

I believe that somehow during the backfires I blew a chunk of that cat out. It doesnt seem plugged, but I do think it may be missing peices and such, I drove a 60 mile round trip today and no rattle at all in the exhaust, I think it blew out the chunks that were in there. a new Bosal Y with cats is on the way to replace them. I still had around a 80 to 100 degree consistant temp difference between cats with the driver side being the cooler.

So from here. Check your wires and swap parts bank to bank not just cyl to cyl when checking components. Replacing the cats is on the schedule.