engine knock... 3-4k only?

wfo9 · May 17, 2016

I have a 2014 GMC SLT seiarra with the 5.3.

Been pretty good overall. My wife drives it daily, but I use it to tow my rock crawler.

I've noticed it has some knock or some type of valve clatter noise around 3-4k rpms under heavy load. It seems to go away at 4k, but is pretty consistent in the 3-4k range.

Just curious if anyone has had a similar issue. I'm planning to have her take it to the dealer since it is about to hit 60k, which I think is the end of the powertrain warranty.

We have had one other problem with the truck. The AC line cracked and needed to be replaced. Besides that, it has been solid. gets great MPG....

thewhitestallion · May 17, 2016

try using premium gas to prevent detonation. Also your powertrain warranty is until 100k. they did not change the powertrain warrant until 2016 year models and they have the 60k / 5yr power train warranty.

wfo9 · May 17, 2016

try using premium gas to prevent detonation. Also your powertrain warranty is until 100k. they did not change the powertrain warrant until 2016 year models and they have the 60k / 5yr power train warranty.

Yea, premium fuel was the first thing I tried... Good to hear the powertrain is good to 100k, Someone told her 60k...

thearizonacowboy · May 17, 2016

Probably an AFM lifter... Can you keep us updated with what you find out?

wfo9 · May 17, 2016

Probably an AFM lifter... Can you keep us updated with what you find out?

Will do. That was another thought I had... It sounds more like valvetrain noise than engine knock (specifically on the drivers side). It does seem to go away at higher RPM, but there is also a slight miss or feel of balance change occasionally at higher RPM.

The motor rarely sees anything over 2500 RPMs when she drives it... But when I'm towing, it gets a solid workout and often results in sub 10mpg trips in the hills.....

TJay74 · May 18, 2016

If she babies it all of the time it may need to be driven hard to clean out the carbon, other though would be to run some fuel injector cleaner thru it and or a Seafoam treatment. If you are not running a catch can the oil that is re-directed via the PCV system has been known to cause detonation and noise over time.

scott19677 · May 18, 2016

If its under warranty I wouldn't suggest any Seafood treatment or home remedies quite yet. The dealer will just blame you for the problem. Take it in let them look at it first. Knock in an 11 to 1 compression engine with hypereutectic pistons is a no no even with Variable Valve Timing.

Thomcat · May 18, 2016

Might want to verify if it is rpm specific or power specific under load to rule out a lifter. Lock in a manual gear and subject it to the same load in different gears and see if the knock comes at the same or a different rpm or disappears in a lower gear.

wfo9 · May 19, 2016

She took it to the dealer today. I'm curious to see what they come up with. My past experiences with dealers have been less than stellar. If they try to sell some BS service... I'm not going to be happy. I just got the firs call from the service advisory saying..."we are going to need to charge you a $129 diagnostic fee and you know this might be hard to reproduce". If nothing else, at least this will be a record that we tried to get them to fix it if something goes way bad down the road.

I probably should have done more troubleshooting on my own, but I've been pre-occupied with my offroad projects plus work. I actually have HP tuners... I used to tune LS1s for forced induction years ago, but have been out of that for many years.. It would have been interesting to see if any knock retard was being logged or learned in that RPM range.

As far as the PCV goes. I usually run a catch can on most of my port injected motors, but I thought they had finally come up with a much better systems for these DI motors. This is my first DI, so I'm not familiar with their quirks yet, I understand there is no longer fuel flowing over the backside of the intake valve and this can lead to some buildup.. from the PCV blowby mist,. but I can't see that causing knock (more like airflow issues).

I'll update this post as I learn more....

GsBowtie · May 19, 2016

That's bs imo to say they will charge you 129 diagnosis fee. Hold your ground, it was brought in for a warranty issue. They need to address it.

wfo9 · May 19, 2016

One call with the service writer so far... The tech could not reproduce it...... Pretty much exactly what I expected, but he did say I could come down tomorrow and he would go for a ride with me. He also said they would have one more guy drive it this evening to see if he could reproduce it.

No codes or misfires detected... Well no shit....

I'll bet they did not even scan it to see if KR is being detected..

Ah, the joys of dealing with dealer service..Kid seems nice enough though, so hopefully we .can get it figured out.

wfo9 · May 21, 2016

Just to update, since I hate when people never follow up on issues.

Went to dealer to test drive with service writer... and it had stopped doing it. I could not reproduce.

They were cool and did not charge me... I'll see what happens next time I tow. The strange thing is is was doing it consistently with out the trailer hooked up the day before.

wfo9 · May 21, 2016

Just to update, since I hate when people never follow up on issues.

Went to dealer to test drive with service writer... and it had stopped doing it. I could not reproduce.

They were cool and did not charge me... I'll see what happens next time I tow. The strange thing is is was doing it consistently with out the trailer hooked up the day before.

If it starts again. I'll do some data logging.....

b1gted · May 21, 2016

I have found that recording a video when the issue is happening helps. I have always had good luck capturing the sounds that I hear inside the cab when I think something odd is happening. Nothing yet with my 2016, but on my 2014, I had a left turn steering knock that happened about every 5 turn a left turn a speeds under 5 miles and hour and the service department said they could never hear it, so I got about 5 videos with it happening and they at least believed me and attempted to find the issue.

thewhitestallion · May 22, 2016

I have found that recording a video when the issue is happening helps. I have always had good luck capturing the sounds that I hear inside the cab when I think something odd is happening. Nothing yet with my 2016, but on my 2014, I had a left turn steering knock that happened about every 5 turn a left turn a speeds under 5 miles and hour and the service department said they could never hear it, so I got about 5 videos with it happening and they at least believed me and attempted to find the issue.

This is true, i had issues with my radio messing up on my 14 and I knew that if I took it in they would say that they could not reproduce it. So I began taking videos and when I showed the service writer he could no argue and put it in my paperwork that I had video of the radio messing up. They updated my radio under warranty and I was good for about 15k more miles but now it is starting to do it again... I need to take it back for the radio and my driver seat moving but honestly I hate not having my truck.