2014 Sierra 5.3……..low compression on cylinder #7 ?????

wink05 · June 5, 2015

This truck has 962 miles on it, and as I was driving it yesterday, approaching a red light, it began to develop a miss….as if you had pulled a spark plug wire off or something. Two blocks later the check engine light comes on, and another two blocks the stablitrak light comes on, and the transmission is shifting hard.

Now the dealer is in the early stages of checking it out, but is certain it's something internal, as "cylinder #7 has very low compression". Said he will update me next week!!?? I'm not at all thrilled about the need to tear into the motor on a truck this new.

Has anyone else experienced or ever heard anything like this?

Thanks for any and all help.

hurricanoday · June 5, 2015

yea I have heard lots about machines breaking. Sounds like your dealer is working with you and should be replaced under warranty. Did they give you a rental?

Green 1364 · June 5, 2015

If you own it less then 30 days you can get all your money back.

jamin87ss · June 5, 2015

I know its hard for us to understand, but this does happen, things break, when I drive tow truck I towed more new cars then anything, it sucks, now if there were 500 people on here with this issue I'd get worried, they will handle it, be diligent they will take care of you,

wink05 · June 5, 2015

I understand things will break…………..but a new vehicle (18 months old)………..with less than a 1,000 miles?

And major internal issues? Not a happy camper!!

TJay74 · June 5, 2015

If you own it less then 30 days you can get all your money back.

Where did you get this info from, I have yet to hear from any state that will force a manufacture to take a vehicle back because of an issue that is covered under warranty just for being less than 30 days old. That is what the warranty is for and the reason it is there. Things happen, there are 750k 2014/15 trucks on the road, there will be mechanical failures along the way. Let the dealership do its job and diagnosis the issue and fix it.

dagwood2001 · June 5, 2015

I understand things will break…………..but a new vehicle (18 months old)………..with less than a 1,000 miles?

And major internal issues? Not a happy camper!!

you've had your truck for a year and a half and have less than 1,000 miles on it? what do you drive it to the end of the driveway and back to pick up the paper and mail and that's it?

as others have said, let the dealership take a crack at it. i actually trust them a lot more with engine issues than i do electrical stuff, knocks and rattles, etc....those are things which seem to hard to fix. i'm sure it will work out fine.

and LOL at "they have to take it back within 30 days". on what planet?

Green 1364 · June 6, 2015

Where did you get this info from, I have yet to hear from any state that will force a manufacture to take a vehicle back because of an issue that is covered under warranty just for being less than 30 days old. That is what the warranty is for and the reason it is there. Things happen, there are 750k 2014/15 trucks on the road, there will be mechanical failures along the way. Let the dealership do its job and diagnosis the issue and fix it.

Meant 3 days not 30. Happened to me in Pa. dealer caved in my front fender.

arkenzo · June 6, 2015

Meant 3 days not 30. Happened to me in Pa. dealer caved in my front fender.

Dude, totally different situation!

newdude · June 6, 2015

This truck has 962 miles on it, and as I was driving it yesterday, approaching a red light, it began to develop a miss….as if you had pulled a spark plug wire off or something. Two blocks later the check engine light comes on, and another two blocks the stablitrak light comes on, and the transmission is shifting hard.

Now the dealer is in the early stages of checking it out, but is certain it's something internal, as "cylinder #7 has very low compression". Said he will update me next week!!?? I'm not at all thrilled about the need to tear into the motor on a truck this new.

Has anyone else experienced or ever heard anything like this?

Thanks for any and all help.

Betting pretty strongly that an AFM lifter either unlocked from the lifter bucket or the pin failed and the lifter is in the AFM position and not opening a valve.

wink05 · June 6, 2015

Betting pretty strongly that an AFM lifter either unlocked from the lifter bucket or the pin failed and the lifter is in the AFM position and not opening a valve.

Sounds like a reasonable explanation. I appreciate the info.

HondaHawkGT · June 7, 2015

+1 On a bad AFM lifter.

I've also heard of one or two cases where GM AFM engines developed low compression because the rings didn't seat properly and the rings just happened to rotate to where the gaps were inline and blowing by. Gap was on the high end too.

These things happen. I read or hear of plenty Ecoboosts and Ecodiesels that let go at low mileage. Just gotta look at a few message boards to find that out.

GRN69CHV · June 7, 2015

Started another thread where mine did same thing last week with just over 9000 miles on it. I was thinking failed cat due to heat buildup from stuck adaptive exhaust valve. Dealer says failed injector driver side. Engine miss is one thing, I found it odd for stabilitrak to act up and trans to shift hard

GRN69CHV · June 9, 2015

Basis for these motors are the LS series. Bottom end is well proven design. Know a couple guys that run LS motors (bought with over 100K on them) in turbocharged drag cars, running 18-22 psi boost. Even if the ring gaps did align, compression loss is insignificant, biggest issue would be some increase in blow-by and long term cylinder wear depending on if the gaps ended up on the thrust side.

wink05 · June 10, 2015

Just a quick FYI……picked up the truck this afternoon, and written on the repair ticket:

"968 STUCK AFM LIFTER CYLINDER NUMBER SEVEN 4062410 3073 6.70 PERFORMED OBD CHECK P0300. MISFIRE CYLINDER SEVEN. SWAPPED PLUG WIRE AND COIL WITH CYLINDER ONE, DID NOT CHANGE. PERFORMED MULTIPLE INJECTOR BALANCE TESTS USING GDS. ALL BETWEEN 30 AND 40 PSI DROP. PERFORMED DYNAMIC COMPRESSION TEST LEFT BANK ONLY. CYLINDER SEVEN 50 PSI ALL OTHERS 100+ PSI. REMOVED VALVE COVER INSPECTED ROCKER ARMS AND VALVE SPRINGS ALL OK. REMOVED CYLINDER SEVEN PISTON INSPECTED ALL OK PISTON AND RINGS PROPERLY INSTALLED. REINSTALLED PISTON REPLACED TTY ROD BOLTS. REINSTALLED OIL PAN REPLACED PICKUP AND HIGH PRESSURE SEALS. DETERMINED AFM LIFTER PARTIALLY LOCKED NOT FULLY OPENING VALVE. REPLACED BOTH INTAKE AND EXHAUST AFM LIFTERS CYLINDER SEVEN.