All bank 2 cylinders misfire

[AmunRoo]

Hey there! So I'm going to need some help and I'm hoping I can find it here. Here's the background, I was driving home on the expressway and I started getting a flashing check engine light and I know I had misfires. I hooked up the skin tool and found that the entire bank 2 cylinders were misfiring. Next day I started poking around and figured I'd check the catalytic converter. It turns out it was toast. The element inside the cat was completely destroyed and it plugged up the catalytic converter. Took it to a shop and had both cats replaced. Shop claims they looked around and removed all catalytic material from the tubing. So now the truck was driving fine with no issues. The night before I'm driving back home and I start getting random misfires on Bank 2 again. I had previously changed out all the plugs and wires on bank 2 a few days ago. So I know the plugs and wires are not the culprits. The misfires will occur for a bit and then go away in the truck will run fine. And then they'll come back again. Not really sure what to make of it. I'm going to check for some vacuum leaks and possibly swap out all the coils on Bank 2. Has anyone experienced this type of issue before? I did throw the borescope into the bung weld for the downstream o2 sensor and there were no obstructions.

I'm sorry it was a little long, but I figured I would have to add in all the details. As always any help is greatly appreciated!

 

[OR VietVet]

Check all wiring connection(s) at the coils and injectors on that side and the ground for those. Had another recent rig on here with a whole side misfiring and was the ground. Did you do the oxygen sensors?

 

[Geotrash]

Check all wiring connection(s) at the coils and injectors on that side and the ground for those. Had another recent rig on here with a whole side misfiring and was the ground. Did you do the oxygen sensors?

+1

 

[AmunRoo]

I only changed the down stream on the passenger side, which was the destroyed Cat. I also checked all the wiring for the injectors and coils. The wires were intact. But, I just slapped the scanner on the truck and I got a new trouble code, p0174. So apparently I'm not showing a lean condition on bank 2. I'm guessing I'm going to have to do a smoke test since I didn't see anything obvious. I sprayed a little carb cleaner around the intake and no changes. I'm wondering if it could be as simple as the upstream O2 sensor?

 

[OR VietVet]

How many miles on the engine? Oxygen sensors are meant to be maintenance items. You said new wires and plugs, how long were the old ones around? That cat went bad for some reason and most of the time it is age or poor maintenance on the plugs and wires and fuel systems causing too much fuel delivery but as I said, you can "check" the wires connections but these rigs are known for ground problems.

 

[AmunRoo]

I'm right and around 106k maybe 107 k. I checked all the wiring and it was intact. I'm not too sure on the maintenance I just bought the truck about 10 months ago and it had around 97k. I've only changed the downstream on the bad cat side. I'm planning to change the other three this weekend. I was also looking for possible vacuum leaks but I couldn't find anything that stood out. The MAF is clean as I just took care of that about a month and a half ago. I'm definitely going to look into the ground issue. The problem is that this is an intermittent issue. It doesn't always happen and when it does, it goes away for a little bit and then comes back and then goes away and then comes back, etc, etc...

 

[swathdiver]

Something killed the cat and replacing them with new will only get the new one killed until you find out the problem.

If this is a very early 2007 model, it has AFM components but is not active in the tune. If the metal plate under your black intake manifold is lumpy and not flat, you have AFM. This could mean that you have partially collapsed lifters. Another issue with these early L92s are broken valve springs. A dirty injector can dump fuel or a broken exhaust manifold bolt causing an air leak can trick the computer into dumping more fuel into that side also taking out the cat.

Tech-2 time.

 

[Fless]

Get the scanner out and look at some live data; post up what your long- and short-term fuel trims look like, both banks.

 

[AmunRoo]

Ok, I have an update. First, I'm pretty sure I don't have a FM. The plate underneath the intake manifold doesn't look "lumpy". I posted a pic of the plate as best I could take. Next, I hooked up the smoke machine and I'm getting a ton of smoke coming out of my oil fill tube extension at the base word connects to the valve cover. This would explain all of the unmetered air coming in. So I'm guessing this is the cause of my misfires on bank 2. I have read that you can remove the extension in place the filler kept directly onto the valve cover and have no issues ever again. It kind of sucks that you have to remove the valve cover just to replace the tube. As soon as I started running the smoke through the intake tube, I started hearing that big hiss right away. Once the smoke reached the tube, I was relieved. Hopefully, eliminating this tube well forever solve this issue. So I guess it's time to go to work

 

[AmunRoo]

Popped that sucker right out! So far so good. Let's see what happens over the next few days.

 

[NorwegianHoe]

Popped that sucker right out! So far so good. Let's see what happens over the next few days.

Just found out my filler hose is not even attached, did your fix and going to test tomorrow as it's late here. Thanks for this documentation (Probably not the cause of my terrible p0300 tho, but I'll sleep in the hope tonight)

 

[89Suburban]

Popped that sucker right out! So far so good. Let's see what happens over the next few days.

The filler necks on these SUCK. I bought brand new ones and they still wobble and leak. I just left it off and put the cap right on the cover like you have it. I have a funnel that fit's in that pocket perfectly when I have to add oil.