Any 6.2L experts here? New owner with questions

[whistleblower]

Recently purchased a 2020 Yukon XL with 60k miles with the 6.2L.  Fleet car and was told maintenance was is up-to-date but who the heck knows.  

 

My questions after ~1,000k miles of driving split between city and highway:

 

1 - I feel light surging at various RPMs and various speeds.  Its hard to recreate but I'll be driving, will forget about it and then will feel it again.  Typically happens on acceleration but I noticed it the other day at ~70-75.  Any ideas?  Seems to happen mostly at low rpms but I have not been able to define the pattern.  

2 - Rough idle.  I'll be sitting at a stop light, not thinking about it, and will suddenly feel a shake, almost like a miss.  Same characteristics when starting cold and when warm.  Almost more apparent when warm.  

3 - Less of a concern but just want to confirm that this is normal.  After the engine is warm, my oil pressure drops to ~18-20 when at a stop light, then jumps up to ~40 when underway.  Oil is full.  Confirm this is normal?  

 

Regarding 1 and 2, I'd love input from people who know these motors.  I've done a bunch of reading and have an appointment with a dealership to see if they can find anything [which, honestly, I'd love to cancel - terrified of the potential bill].  I hate to self diagnose as I'm not a mechanic but have found posts referencing new plugs/wires as a fix as well as removing carbon from the intakes.  

 

Any ideas?  If its as simple as new plugs/wires, I'm going to cancel the dealership visit and find a local mechanic to do that.  

 

For those with higher miles on your 6.2, how often are you cleaning the carbon?  

 

The power of this engine is awesome but honestly I've been a little disappointed with the overall driving experience.  My previous car to this, 20+ year daily driver, a 2000 F150 with the "terrible" 5.4 triton @ 200k miles, is much smoother than my shiny new(ish) Yukon.... which makes me think its something that can hopefully be corrected!

 

Thanks in advance

[JimCost2014]

3 hours ago, whistleblower said:

3 - Less of a concern but just want to confirm that this is normal.  After the engine is warm, my oil pressure drops to ~18-20 when at a stop light, then jumps up to ~40 when underway.  Oil is full.  Confirm this is normal?  

Normal.

 

1st symptom might actually be your torque converter on it's way to failure, are you feeling any vibration/rumble strip effect when it surges?

 

Some have changed the plugs at your mileage and noticed a smoother idle.

[Black02Silverado]

The first part might be DFM,  Dynamic Fuel Management.  Something that you are not use to and it could be what you feel.  Other than that not sure.

 

The second like Jim said it is normal.  Oil pressure is controlled by a variable displacement pump and so it changes as demand for oil pressure changes.

[NWI Denali]

As stated the oil pressure is normal. The vibration your feeling and at the speed you're saying sounds similar to the torque converter shuddering the 8L90 gets but you have the 10 speed so thats strange. The rough idle is normal to an extent- how much do your rpms drop? The ecu is programmed to idle these engines so low to save fuel economy that some "stumbling" is normal. They idle at like 500 rpm in gear 

[Blueman]

My truck does same thing when feathering the gas sometimes it feels like you’re going over a rumble strip it is a 2020 Sierra with a 5.3 motor and ten speed transmission dealer says they can’t reproduce issue

[elcamino]

Well if it was a fleet car as you say they could have and probably did use low octane fuel.  IMO these motors run best on premium fuel. I would use a good (AMSOIL P.i. for instance) fuel system additive for several tanks and these concerns might go away.

[swathdiver]

On 7/22/2021 at 10:15 AM, whistleblower said:

Recently purchased a 2020 Yukon XL with 60k miles with the 6.2L.  Fleet car and was told maintenance was is up-to-date but who the heck knows.  

 

My questions after ~1,000k miles of driving split between city and highway:

 

1 - I feel light surging at various RPMs and various speeds.  Its hard to recreate but I'll be driving, will forget about it and then will feel it again.  Typically happens on acceleration but I noticed it the other day at ~70-75.  Any ideas?  Seems to happen mostly at low rpms but I have not been able to define the pattern.  

2 - Rough idle.  I'll be sitting at a stop light, not thinking about it, and will suddenly feel a shake, almost like a miss.  Same characteristics when starting cold and when warm.  Almost more apparent when warm.  

3 - Less of a concern but just want to confirm that this is normal.  After the engine is warm, my oil pressure drops to ~18-20 when at a stop light, then jumps up to ~40 when underway.  Oil is full.  Confirm this is normal?  

 

Regarding 1 and 2, I'd love input from people who know these motors.  I've done a bunch of reading and have an appointment with a dealership to see if they can find anything [which, honestly, I'd love to cancel - terrified of the potential bill].  I hate to self diagnose as I'm not a mechanic but have found posts referencing new plugs/wires as a fix as well as removing carbon from the intakes.  

 

Any ideas?  If its as simple as new plugs/wires, I'm going to cancel the dealership visit and find a local mechanic to do that.  

 

For those with higher miles on your 6.2, how often are you cleaning the carbon?  

 

The power of this engine is awesome but honestly I've been a little disappointed with the overall driving experience.  My previous car to this, 20+ year daily driver, a 2000 F150 with the "terrible" 5.4 triton @ 200k miles, is much smoother than my shiny new(ish) Yukon.... which makes me think its something that can hopefully be corrected!

 

Thanks in advance

Check your driver's side engine mount for leaks.  If it is broken, it will transmit more engine vibrations into the cab.

 

More importantly, what kind of fuel are you using?  These are high compression performance engines, they are not intended to burn anything less than 91 octane gasoline.  Even then, some brands like Shell, deliver less performance compared to Sunoco for example.  The manual may say you can run it, it's a sure fire way to bust a ring or piston.

 

Oil pressure is about normal, a little low.  If the oil is over 5000 miles old, don't let it get older, it's plumb wore out.  Fresh oil will bring the pressure back up.  A Mobil 1 Extended Performance oil filter will lower your oil pressure 2-3 psi compared to the factory filter.

[lucas287]

Any claims about an L86 being incompatible with 87 octane fuel is nothing but rhetoric and hearsay. I've data logged A LOT and tried many different octanes and timing advance curves. My educated opinion is that it can, and will, run just fine on it. You won't bust a ring or piston if your sensors are working. That's what knock sensors are for. The stock sensor calibration is VERY sensitive. Fill with 87, the knock sensor will immediately start pulling timing if it's over 3* of knock. The spark tables will oscillate between the low and high octane tables at any given rpm/load and extrapolate according to detected knock. In the summer on 87 octane in top gear rolling down the highway you'll probably be running single digit advance on slight grades. Does the 6.2 have the torque to not care? Yep. Is it the best running setup? Nope. Will it spontaneously explode because of it? Nope. Mine hasn't anyways. I almost exclusively run 87 or some concentration of ethanol up to e80. 89 or 93 just isn't cost effective for me. 

 

Alright, off my soap box. And I mean no disrespect @swathdiver. 

 

Like others have said, oil pressure is fine. I run 5W-30 since that's the same weight my wife's turbo SUV calls for so I just buy oil in bulk. I've noticed I get quite a bit more pressure compared to 0w-20. I also burn less throughout a 5k mile OCI. 

 

I've never liked the way my truck idles. Bumping the RPM can help quite a bit. I'm at 625 right now and it's pretty good. Mostly, though, these torque-based ECMs are finicky. They want expected airflow to equal actual airflow. When there's a disconnect - they start acting weird. For example, let's say because of sensor degradation and your combination of air filter, exhaust flow, etc.. you're making more torque at idle than it's expecting. It will pull timing (torque management advance is the PID) to reduce torque to the "expected" amount. but then it will make too little torque, so it adds advance, and then pulls it again. Just watch your timing advance. it's not the like old days with distributors - it will jump around a lot. The closer reality is to expected, the smoother it will be. 

 

This goes for all the quirkiness of my truck. I've been able to make it run significantly smoother (and peppier) with a lot of datalogging and tuning. trial and error. and it's taken over a year  and still not perfect. 

[swathdiver]

4 hours ago, lucas287 said:

Any claims about an L86 being incompatible with 87 octane fuel is nothing but rhetoric and hearsay. I've data logged A LOT and tried many different octanes and timing advance curves. My educated opinion is that it can, and will, run just fine on it. You won't bust a ring or piston if your sensors are working. That's what knock sensors are for. The stock sensor calibration is VERY sensitive. Fill with 87, the knock sensor will immediately start pulling timing if it's over 3* of knock. The spark tables will oscillate between the low and high octane tables at any given rpm/load and extrapolate according to detected knock. In the summer on 87 octane in top gear rolling down the highway you'll probably be running single digit advance on slight grades. Does the 6.2 have the torque to not care? Yep. Is it the best running setup? Nope. Will it spontaneously explode because of it? Nope. Mine hasn't anyways. I almost exclusively run 87 or some concentration of ethanol up to e80. 89 or 93 just isn't cost effective for me. 

 

Alright, off my soap box. And I mean no disrespect @swathdiver. 

 

Like others have said, oil pressure is fine. I run 5W-30 since that's the same weight my wife's turbo SUV calls for so I just buy oil in bulk. I've noticed I get quite a bit more pressure compared to 0w-20. I also burn less throughout a 5k mile OCI. 

 

I've never liked the way my truck idles. Bumping the RPM can help quite a bit. I'm at 625 right now and it's pretty good. Mostly, though, these torque-based ECMs are finicky. They want expected airflow to equal actual airflow. When there's a disconnect - they start acting weird. For example, let's say because of sensor degradation and your combination of air filter, exhaust flow, etc.. you're making more torque at idle than it's expecting. It will pull timing (torque management advance is the PID) to reduce torque to the "expected" amount. but then it will make too little torque, so it adds advance, and then pulls it again. Just watch your timing advance. it's not the like old days with distributors - it will jump around a lot. The closer reality is to expected, the smoother it will be. 

 

This goes for all the quirkiness of my truck. I've been able to make it run significantly smoother (and peppier) with a lot of datalogging and tuning. trial and error. and it's taken over a year  and still not perfect. 

 

I'm more familiar with the previous generation Lucas.  However, in my mind, it runs counter to common sense to pump low octane fuel into a 10.5:1 motor and let the knock sensor ****** the timing every time it detects knock.  So the motor is constantly knocking at some level while being driven for the computer to pull timing and run on the appropriate map.  What I think validates this thinking are all of the posts on these truck forums of folks with 6.2 motors with busted rings and pistons and when queried, find out that their engines were fed a steady diet of low octane swill.  

 

I was wrong about the Gen V 5.3 benefitting from higher octane fuel, a friend tested his for a spell and proved me wrong, the first time in 30 years but none of the other engines were direct injected and gasoline powered.

 

I like the idea of the newer Ram and Toyota trucks determining the octane rating and running the appropriate tables like ours do on ethanol.

 

We also rarely run on 93 and run a mix of ethanol and gasoline for best bang for the buck and mileage.  The Yukon XL gets better gas mileage running 16-20 percent or so compared with Chevron E10, the best 'round these parts.  We're still working on the Sierra, she thus far seems to like E15 or E50 better than 93.  Both motors love burning E70-E85 but that too is not always convenient or cost effective.

 

No disrespect intended here either, I profess to not know everything and my wife concurs!  

 

Oh, yes, mine idles much smoother with the idle turned up some, I had BlackBear set it at 625 for me.

[elcamino]

Well, I guess you have a decision to make.  Follow the oem manual recommendations;

Quote

Premium unleaded gasoline
meeting ASTM specification D4814
with a posted octane rating of 93 —
(R+M)/2 — is highly recommended
for best performance and fuel
economy. Unleaded gasoline with
an octane rated as low as 87 can be
used. Using unleaded gasoline
rated below 93 octane, however, will
lead to reduced acceleration and
fuel economy. If knocking occurs,
use a gasoline rated at 93 octane
as soon as possible, otherwise, the
engine could be damaged. If heavy
knocking is heard when using
gasoline with a 93 octane rating, the
engine needs service.

Or follow the recommendations of experts on this forum...

[lucas287]

27 minutes ago, elcamino said:

Well, I guess you have a decision to make.  Follow the oem manual recommendations;

Or follow the recommendations of experts on this forum...

 

Nothing stated in the manual contradicts what was stated above. 

[lucas287]

11 hours ago, swathdiver said:

pump low octane fuel into a 10.5:1 motor

even worse - it's 11.5:1 - but it's not really apples to apples compared to port injection. direct injection cools the chamber much better and therefore knock resistance is inherently increased. It's all in the design of the chamber, and how the valve events work together. I remember when Mazda debuted Skyactiv - that little 2.5 4 cylinder had 13.5:1 compression and ran fantastic on 87 octane (we had a little CX-5 for many years). 

 

Yep - also agreed with the ethanol blend. I have a flex fuel sensor and have all those tables calibrated and such and I get equal performance and economy on e20-e30 as 93 octane for a LOT less money. 

[Grumpy Bear]

There is knock the sensor hears you will not. Then there is knock you will hear that is beyond the tune of the motor under whatever conditions are currently present. That knock will break stuff in a hurry. Something is drastically wrong. YOU should never hear it ping....ever. These sensors can hear a gnat fart in a hurricane. 

 

I always learn something new it these types of threads. I did not know Lucas that it 'searches' various tables but it makes sense. Also explains why every once in awhile I'll still see a bit of KR even on E-85. (75% test) I guess it gets caught in a compromising situation at times. 

 

FYI DGI helps charge cooling yes but VVT controlling IVC angle is what keeps high compression motors happy on low octane fuel. Cylinder pressure is King. 

[diyer2]

Well my memory isn't what it used to be. Back in the 70's when I was racing 1/4 mile we adjusted timing for better performance. We also changed distributor weights to change timing curve. I do remember spark knock and blown engines. Everything has a limit.

I don't own a big block but you can bet I wouldn't cheap out on gas for it. I believe the engineers are smarter than me. We put a man on the moon with a slide rule I believe. The movie Hidden Figures come to mind. 

[KARNUT]

9 minutes ago, diyer2 said:

Well my memory isn't what it used to be. Back in the 70's when I was racing 1/4 mile we adjusted timing for better performance. We also changed distributor weights to change timing curve. I do remember spark knock and blown engines. Everything has a limit.

I don't own a big block but you can bet I wouldn't cheap out on gas for it. I believe the engineers are smarter than me. We put a man on the moon with a slide rule I believe. The movie Hidden Figures come to mind. 

The first thing always was advancing the distributor. Pinging could be heard. Sometimes the starter dragging was an indicator of too much timing. My 454 impala had a ignition switch I added so after I was wheeling it over I turned on the spark to light it’s fire. I kept me from blowing the nose off the starter. There was a definite performance advantage.