#7 Cylinder Misfire

[T-Town-Z]

I did a search here for it but came up empty. Last week, my Check Engine Light came on briefly while on the highway. Just before and after that I noticed a reduced lack of response to giving it more throttle. I had a local guy pull the CEL code and said it came up as #7 Cylinder Misfire. I'm at 55,000 miles and am off warranty. The truck is a '14 with a 5.3.

Any suggestions, or thoughts how serious this may be ?

[newdude]

55k you should still have powertrain. Could be as simple as a fouled plug, fuel injector, or as bad as a busted AFM lifter or bent rod.

[T-Town-Z]

I guess it might still be covered under the Powertrain Warranty. It just surprises and worries me that nobody on here has had a similar code come up.

[txab]

https://www.google.com/search?hl=en&as_q=cylinder+7+misfire&as_epq=&as_oq=&as_eq=&as_nlo=&as_nhi=&lr=&cr=&as_qdr=all&as_sitesearch=www.gm-trucks.com&as_occt=any&safe=images&as_filetype=&as_rights=

[T-Town-Z]

Well, after reading some of those links, it looks like I'm going to have to go visit the dealership. Doesn't look like anything I'll be able to check myself .... I'll post back when I get an answer.

[newdude]

I guess it might still be covered under the Powertrain Warranty. It just surprises and worries me that nobody on here has had a similar code come up.

 

What code? P0307? (didn't see a code above posted). Cylinder 1, 4, 6 and 7 are AFM cylinders. If you had a P0307 on an 07-13 truck, I'd say you need a spark plug and a new driver's side valve cover. But, Gen 5 engines? Different. We've seen here at work bad AFM lifters, and bent push rods. Couple hosed injectors. We had one 5.3 a few weeks ago, low miles, like 40k? Had a busted AFM lifter with a miss on the cylinder. Tech puts it together, and sure as shite a rod on an AFM lifer on the OTHER bank was bent. That cylinder didn't misfire until the truck was put back together. Could you have a loose wire? Bad plug? Sure.

Edited March 7, 2017 by 15HDriver

[T-Town-Z]

Unfortunately I didn't get the code when the guy pulled it for me. I've never messed with the plugs or wires, so they shouldn't be loose ..... but who knows ? I had been towing my tractor a couple times the week before, so maybe something about the extra load could have provoked it to throw a code.

.

As a side note for those reading, I called the dealership's service department and the guy told me the code will stay on file for 40 start/stop cycles, then drops off. As for the cost being covered by the powertrain warranty, it only covers the mechanical hard parts, like the lifters, rods, pistons ....that kind of stuff. If it turns out to be a fuel injector, spark plug, wire, coil pack, etc, It'll be at my expense. I'm taking it to them in the morning .... guess I'll know something soon enough.

[T-Town-Z]

Update - I took the truck in to the dealership on Wednesday and got a phone call this afternoon (Friday). He said they verified all the external components were good and believe it may be internal engine issues. The service manager asked me specifically if I or anyone had done ANY tunes or modifications to the computer, because they were going to have to send the computer program in to GM. Said this is for verification and to get authorization from them to open up the engine. Lucky for me, I have held off getting a tune on it so far. He said if there was any "non-GM" programming, that GM would null covering the engine examination and repairs under warranty. He was very clear about it and wanted to know there would be no issues if he sends it in.

Really glad I held off on the tune ..... but it makes me wonder, if I had tuned it and turned off the AFM, maybe I wouldn't have had this problem ???

Guess I'll know more next week.

[T-Town-Z]

 

What code? P0307? (didn't see a code above posted). Cylinder 1, 4, 6 and 7 are AFM cylinders. If you had a P0307 on an 07-13 truck, I'd say you need a spark plug and a new driver's side valve cover. But, Gen 5 engines? Different. We've seen here at work bad AFM lifters, and bent push rods. Couple hosed injectors. We had one 5.3 a few weeks ago, low miles, like 40k? Had a busted AFM lifter with a miss on the cylinder. Tech puts it together, and sure as shite a rod on an AFM lifer on the OTHER bank was bent. That cylinder didn't misfire until the truck was put back together. Could you have a loose wire? Bad plug? Sure.

15HD called it right ! Once they got into the engine, they found the AFM lifter on #7 had failed. It took 2 weeks in a loaner, but I finally have mine back and the full cost was covered under the Powertrain Warranty. I know some people have issues with their dealerships, but the GMC service center here in Broken Arrow, OK has been good to me so far !

[newdude]

15HD called it right ! Once they got into the engine, they found the AFM lifter on #7 had failed. It took 2 weeks in a loaner, but I finally have mine back and the full cost was covered under the Powertrain Warranty. I know some people have issues with their dealerships, but the GMC service center here in Broken Arrow, OK has been good to me so far !

 

Good to hear you are all fixed up! Honestly, its sad that this has been popping up lately. I think I'll have to buy some stock in Range really soon LOL as more and more GM guys will be turning AFM off. I don't know what GM did, but some of me thinks the switch to 0w20 and oil aeration from that might have something to do with the lifter failures which then turn into pushrod failures. Sucks. But, on the same note, there are quite a few folks that have had zero issues.

[14silverado5.3]

I had that happen to me on my 2014 Silverado. Mine was the #8 and happened at 8,000 miles...

[dasimmon]

 

What code? P0307? (didn't see a code above posted). Cylinder 1, 4, 6 and 7 are AFM cylinders. If you had a P0307 on an 07-13 truck, I'd say you need a spark plug and a new driver's side valve cover. But, Gen 5 engines? Different. We've seen here at work bad AFM lifters, and bent push rods. Couple hosed injectors. We had one 5.3 a few weeks ago, low miles, like 40k? Had a busted AFM lifter with a miss on the cylinder. Tech puts it together, and sure as shite a rod on an AFM lifer on the OTHER bank was bent. That cylinder didn't misfire until the truck was put back together. Could you have a loose wire? Bad plug? Sure.

if afm had been turned off, would this have prevented the issue for t-town-z?

[newdude]

if afm had been turned off, would this have prevented the issue for t-town-z?

 

 

I wish I had one of these trucks to test that myself. I do recall GM having some mention of oil aeration in their AFM lifter bulletin for these engines.

 

Cause

This may be the result of an active fuel management (AFM) lifter that is mechanically collapsed and/or stuck all of the time.

 

This may be the result of internal locking pin damage in the lifter, due to oil aeration.

 

This may be the result of a lifter that has collapsed and is stuck in the lifter bore.

Condition

Some customers may comment on a malfunction indicator lamp (MIL) on and/or an engine misfire/tick noise.

 

Technicians may find DTC P0300 set or in history.

 

To me...that says 0w20 and maybe those fancy dual stage pumps gets the oil worked up and aerates it, thus causing the pins in the lifters to fail.

 

On the AFM lifters on the OHV engines, the VLOM solenoids send oil pressure (oil) to the lifters and they force the locking pins closed. When the solenoids close, they pull oil away from the lifters and the pins lock and you have all 8 cylinders.

 

Lets say you disable AFM. Now, you have no chance to send that oil pressure to the AFM lifters to unlock the pins. You've just eliminated a chance for aerated oil to unlock the lifter, and then due to its aeration, suddenly lock the pin while its supposed to be keeping the valves closed, it pushes the valve, whacks the piston and bends the rod and the AFM lifter fails.

 

Its definitely a theory that I wish I could test. On the other hand, on my 2012 1500 5.3, I never disabled AFM, and it saw some strong RPMs quite a bit sometimes, and had zero oil consumption and no AFM lifter issues.

[dasimmon]

 

 

I wish I had one of these trucks to test that myself. I do recall GM having some mention of oil aeration in their AFM lifter bulletin for these engines.

 

To me...that says 0w20 and maybe those fancy dual stage pumps gets the oil worked up and aerates it, thus causing the pins in the lifters to fail.

 

On the AFM lifters on the OHV engines, the VLOM solenoids send oil pressure (oil) to the lifters and they force the locking pins closed. When the solenoids close, they pull oil away from the lifters and the pins lock and you have all 8 cylinders.

 

Lets say you disable AFM. Now, you have no chance to send that oil pressure to the AFM lifters to unlock the pins. You've just eliminated a chance for aerated oil to unlock the lifter, and then due to its aeration, suddenly lock the pin while its supposed to be keeping the valves closed, it pushes the valve, whacks the piston and bends the rod and the AFM lifter fails.

 

Its definitely a theory that I wish I could test. On the other hand, on my 2012 1500 5.3, I never disabled AFM, and it saw some strong RPMs quite a bit sometimes, and had zero oil consumption and no AFM lifter issues.

knowledgeable and informative as always! really enjoy your posts

[T-Town-Z]

I'd be curious to know if these AFM components fail just randomly, or if there is something that may aggravate it ? Like if those who run their trucks hard, or pull loaded trailers ??? I know I don't "baby" mine, but I don't really abuse it either.