2010 Tahoe PPV cylinder misfire

[CrashTestDummy]

Yes, another misfire thread. The CFO came home today saying she noted her truck running rough at idle. Ran okay, otherwise. I went out and checked, and sure enough, at idle it seems to have a miss. Got the OBDII analyzer out and connected it up and 'cylinder 7 misfire'. I forget the code, but will write it down if I have to proceed any further. One odd thing I found was it seemed to blow back into the intake tube/air filter box every time I turned it off. I immediately started checking for a slipped connector on the Air Raid, but everything is tight and in good shape. Whenever you turn the key off, you get a 'chuff' sound under the hood.

The truck has 145K miles on it, and we put plugs and wires on it when we first got it with ~85 K miles on the clock. Other than the vapor canister issue noted elsewhere on this forum, we've had zero mechanical issues with the truck. I'll start with the usual plugs and wires, but anywhere else to check this weekend?

 

[Geotrash]

Yes, another misfire thread. The CFO came home today saying she noted her truck running rough at idle. Ran okay, otherwise. I went out and checked, and sure enough, at idle it seems to have a miss. Got the OBDII analyzer out and connected it up and 'cylinder 7 misfire'. I forget the code, but will write it down if I have to proceed any further. One odd thing I found was it seemed to blow back into the intake tube/air filter box every time I turned it off. I immediately started checking for a slipped connector on the Air Raid, but everything is tight and in good shape. Whenever you turn the key off, you get a 'chuff' sound under the hood.

The truck has 145K miles on it, and we put plugs and wires on it when we first got it with ~85 K miles on the clock. Other than the vapor canister issue noted elsewhere on this forum, we've had zero mechanical issues with the truck. I'll start with the usual plugs and wires, but anywhere else to check this weekend?

The chuff sound makes me wonder if you have an intake manifold gasket gone south?

 

[CrashTestDummy]

I doubt that. It's blowing completely out the TB and intake tract. According to the dedicated driver, everything seems fine except at idle. I get to drive it this weekend.

 

[CrashTestDummy]

Had to run our usual Saturday errands this morning, so took the PPV. It seems to run on all 8 at anything except idle. Romp on it, and it accelerates as I'm accustomed to. When cruising down the road at a steady state, it drops into DOD mode, as usual. When warm, and you start it, it seems to be running on all 8, too, only to drop a cylinder after about 10-15 seconds of running. Weird. Mileage, to me, seems about the same.

Brought home a set of plugs and wires, and we'll start with hole No. 7 first. Probably do that in the morning, as it's been raining all afternoon, and the mosquitoes are riled up. Was hoping to work on the bus this weekend, but I guess not.

 

[SNES Avalanche]

Had to run our usual Saturday errands this morning, so took the PPV. It seems to run on all 8 at anything except idle. Romp on it, and it accelerates as I'm accustomed to. When cruising down the road at a steady state, it drops into DOD mode, as usual. When warm, and you start it, it seems to be running on all 8, too, only to drop a cylinder after about 10-15 seconds of running. Weird. Mileage, to me, seems about the same.

Brought home a set of plugs and wires, and we'll start with hole No. 7 first. Probably do that in the morning, as it's been raining all afternoon, and the mosquitoes are riled up. Was hoping to work on the bus this weekend, but I guess not.

#7 is a AFM / DOD cylinder. It’s possible you’re in the early stages of Lifter failure.

 

[RichardCranium]

#7 is a AFM / DOD cylinder. It’s possible you’re in the early stages of Lifter failure.

Definitely high on the list.

I'd venture to use the KISS method before throwing easy parts at it too, like swapping coils to see if the misfire moves with it.

 

[CrashTestDummy]

#7 is a AFM / DOD cylinder. It’s possible you’re in the early stages of Lifter failure.

I'm really hoping not. I can tell you there are zero odd noises I can hear. I'd expect there to be some extra tapping or rattles if we had a lifter collapsing. We'll start checking things today.

Anyone know where the vapor canister purge valve hose goes into the intake? In the middle of the night (yes, it woke me up) I was thinking that it may be possible that some of the carbon rat turds that escaped the vapor canister when it exploded could possibly have hung that valve open, since I discovered the things in the old valve we pulled off the truck. That's actually the first thing I plan to look at. IF it's jammed open, and IF the line into the intake is in the cylinder 7 intake port, that could cause a too lean condition in that cylinder. Just a thought.

IIRC, it goes into the left side of the intake, but with the long intake tracts in these truck intake manifolds, we could be right there at no. 7.

Edit: The purge valve hose goes into the intake just behind the TB, so no issue there. I even verified it's clean and closed at rest. On to replacing No. 7 plug and wire.

 

[CrashTestDummy]

So FAIL! Finally got the plug wire and plug out. It's under the firewall cowl and just opposite razor-sharp heat shields for the A/C. The guy who makes those heat shields must moonlight for the Ginzu knife company!

Anyway, the plug showed wear, but was dry and the color looked good. Put everything back together and fired it up. Still missing! Checked, and yes, we do have spark. I put a stack of socket extensions together to make a 'stethoscope', and could hear the injector firing. Put the device to the intake side of the head, and back at No. 7 thought I could hear a faint screeching/scraping sound. The shound was not present one port up. Could have been the highly-scientific method I was using, but it's not sounding good.

Since I am essentially one-handed due to a shoulder joint that needs replacing, we're probably going to take the thing to a shop down the street for additional troubleshooting and diagnosis. Hoping it's not a failed lifter, but things now are not looking good. Normally, I'd dig deeper, but there's no way my body is up to pulling front end off the engine bay and yanking the heads off.

 

[CrashTestDummy]

The place I though would do that work said they no longer get that deep into engines. While they offered another company they said they've had good luck with, it's downtown Houston, probably 40 miles away. Since the expense of a possible lifter and cam job may outrun the value of the truck, we're pressing the Easy Button and probably going to replace it sooner, than later. We were planning to update her ride before I fully-retired, so this isn't too far from that date. We've lined up a 2018 PPV and are starting the purchase process.

We may offer this truck up as-is, since it's otherwise a very nice vehicle. Gotta make a decision on that, though.

 

[balln2k11]

Buy a smoker and smoke through the intake and through the oil fill. Might have a vacuum leak.

If you have a rough idle, but everything else is good, I would clean the MAF sensor and replace the purge valve. GM parts are cheap, but labor isn’t. Could also be a bad injector.