engine knock... 3-4k only?

Binobanbino · May 22, 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.

Fuel injection cleaner? Seafoam? Why?

seamus2154 · May 23, 2016

I know the manual says to use 0/20w oil which is pretty light. This is really for fuel mileage I am told. I went in for my free oil change and noticed the put in dexos 5/30w?? I inquired and they said thats what we put in all of them and it runs better here in Florida?? Well I will say it ran quieter and feels better. I had a 14' silverado, 15 sierra, and now a 15 denali. The LT motor has less VT noise w/ the 5/30. I have run 5/30 in all three w/ good results. I just towed 800 miles and motor was purring.

wfo9 · May 26, 2016

I think I'm going to go ahead and run a catch can. I really feel the issue was knock caused from oil in the intake. There is just no way around it with a PCV... I run them on all my motors, but somehow thought they had a better solution in this generation... guess I was wrong.

If anyone has a link to a good one let me know. I'm not paying $400 or some BS like that.

I'll probably go with a generic moroso or somthing unless there is a quality kit at a decent price.

Nathan79 · May 26, 2016

Google the Conceptual Polymer high efficiency version catch can.

HondaHawkGT · May 27, 2016

I know the manual says to use 0/20w oil which is pretty light. This is really for fuel mileage I am told. I went in for my free oil change and noticed the put in dexos 5/30w?? I inquired and they said thats what we put in all of them and it runs better here in Florida?? Well I will say it ran quieter and feels better. I had a 14' silverado, 15 sierra, and now a 15 denali. The LT motor has less VT noise w/ the 5/30. I have run 5/30 in all three w/ good results. I just towed 800 miles and motor was purring.

Yeah GM recommends 5W-30 for the LT1 in the C7 Corvettes but 0W-20 for our trucks. In fact, GM gave the OK to run 15W50 in the new engine when using the Vette on the track. The owner is supposed to drain the oil immediately after finishing any tracking events and replace it with 5w30. It's pretty clear the 20 weight spec is purely a fuel economy driven decision. I'm considering switching to 0W-30 myself.

On a side note, GM was filling the C7 vettes with 5w30 synthetic blend from the factory. Syn blend was on the list of approved oils. Since them GM has revised the list and the engine oil must be full synthetic. No syn blends allowed. From what I've read on the message boards, the vette guys think the syn blend doesn't hold up and oil aeration problems were creating a lot of engine failures and AFM lifter problems.

seamus2154 · May 27, 2016

Yeah GM recommends 5W-30 for the LT1 in the C7 Corvettes but 0W-20 for our trucks. In fact, GM gave the OK to run 15W50 in the new engine when using the Vette on the track. The owner is supposed to drain the oil immediately after finishing any tracking events and replace it with 5w30. It's pretty clear the 20 weight spec is purely a fuel economy driven decision. I'm considering switching to 0W-30 myself.

On a side note, GM was filling the C7 vettes with 5w30 synthetic blend from the factory. Syn blend was on the list of approved oils. Since them GM has revised the list and the engine oil must be full synthetic. No syn blends allowed. From what I've read on the message boards, the vette guys think the syn blend doesn't hold up and oil aeration problems were creating a lot of engine failures and AFM lifter problems.

I have a Zo6 and I run 0/40 all year in Florida and have great oil analysis. Run the 15/50 at track. I thought maybe the tolerances were tighter on our truck engines but based on running 5/30 and the oil pressure I am now thinking no. I towed for 800 miles w/ 5/30, held great oil pressure, still golden brown, and fuel mileage hasn't suffered towing or not.

wfo9 · May 30, 2016

Update, This problem has gotten stranger.

Wife continues to daily drive the truck with no issues. I had lots of towing to do over the weekend, so I installed an air oil seperator/catch can on Friday. My thought was that the noise was engine knock caused by oil in the intake from the PCV...

On Staturday I towed 2hrs away in the hill country and came 2hrs back that evening. Truck ran great with no noise at all. I thought the catch can had solved the problem for sure and was pleased....

Then, on Sunday I towed a shorter 1hr trip. Right as I hit the first hill, the motor started to clatter and it continued the rest of the day. It would start right around 3250 RPM every time under load. Almost like a switch goes off.

Additionally, t I now also hear the same noise on decel under heavy engine breaking. Under tow mode, the motor will occasionally engine break up to about 4500 -5k to maintain speed on a steep grade. I started to hear the same noise there. So it is obviously not knock.

The trick is going to be reproducing this and getting it fixed.... I'm going to try to get some recordings today.

Pretty sure it is not oil related.. It does it when the oil is hot or cool and this is fresh clean oil.

HondaHawkGT · May 31, 2016

Do you have a way to record a video of it and upload it to youtube? It alsmost seeems like you have a valvetrain issue.

thewhitestallion · May 31, 2016

What are you towing and how much does it weigh? Can you tow the trailer to the dealer and let a tech ride in there with you?

wfo9 · May 31, 2016

Here is a recording I made with a camera in the engine compartment. Skip to 1:20 and you can clearly hear it as I pull through a few gears. I tried recording in the cab and it did not really pick it up. With the window down, there is too much wind noise.

Yes, I may have to pull my trailer to the dealer in an attempt to get to the bottom of this, but I'm afraid that won't be enough since it will just be a sound with no other clues.. The weight is about 6k loaded... The truck pulls it fine, but I encounter a lot of hills so the motor needs to work for it...

I've been doing a bit of research on the motor and a couple of things come to mind that could be at play.

1. The high pressure DI fuel pump is actually cam driven and has a lifter of its own... That could be at play....

2. The variable valve timing has specific oil circuits to advance the cam and I'm guessing those are RPM triggered by the ECU. Maybe the one for that RPM and load range is causing some type of valve clearance issue from carbon build up...

Just so strange that it was not happening for day and now it is back. And again, the other odd thing is that the same sound will happen on hard grade braking but at a much higher RPM.

GMCustomerService · May 31, 2016

Hello wfo9,

I am sorry to hear then engine knocking has gotten worse since your last visit and understand your frustrations towards not being able to produce the concern while at the dealership. I would be happy to add an additional layer of support when working with your dealer, please send a private message my way.

Best,

Julianne M.

GM Customer Care

Update, This problem has gotten stranger.

Wife continues to daily drive the truck with no issues. I had lots of towing to do over the weekend, so I installed an air oil seperator/catch can on Friday. My thought was that the noise was engine knock caused by oil in the intake from the PCV...

On Staturday I towed 2hrs away in the hill country and came 2hrs back that evening. Truck ran great with no noise at all. I thought the catch can had solved the problem for sure and was pleased....

Then, on Sunday I towed a shorter 1hr trip. Right as I hit the first hill, the motor started to clatter and it continued the rest of the day. It would start right around 3250 RPM every time under load. Almost like a switch goes off.

Additionally, t I now also hear the same noise on decel under heavy engine breaking. Under tow mode, the motor will occasionally engine break up to about 4500 -5k to maintain speed on a steep grade. I started to hear the same noise there. So it is obviously not knock.

The trick is going to be reproducing this and getting it fixed.... I'm going to try to get some recordings today.

Pretty sure it is not oil related.. It does it when the oil is hot or cool and this is fresh clean oil.