Stutters and backfires - clogged cats?

[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.