2017 Escalade/Denali L86 "requires" 93 octane - your experience?

[Marky Dissod]

I can guarantee anyone running 87 octane has spark knock that either:
they cannot hear because they don’t know what it sounds like,
or the ECM is pulling the timing so much to mitigate the knock at the cost of power.

Sounds like another way of saying, GM did not write the L92 / L9H / L94 Low Octane table properly?
GM did say that one should be able to use 87 with lowered expectations.

Why buy the 6.2L, if $5-$10 extra per fill up to keep your engine safe is an issue? Just buy a 5.3L.

If GM offered a less-prestigious '6.0L that tows & hauls just fine on 87' option,
I bet a lot of people would take GM up on that offer.
I guess I get why Cadillac won't offer an 87 octane 6.0L, but GMC should.

Regardless, the solution is a tune where the Low Octane table is written with 87 in mind.

 

[91RS]

You can’t write a fuel table that works perfectly in all areas of the country, in different weather conditions, with different fuel additives. Once again, if the little difference in the price of fuel is that big of deal, don’t buy the high line vehicle. An engine costs $12k, why would you risk cracking the pistons over $10 per fill up?

The ** version of the 6.0L that came in the GMT-800 Denali, Escalade, and H2 required mid grade, if I remember correctly. The 6.0L that came in the 2500’s and vans up to a few years ago was designed for work and not high performance and only needed 87. The 6.6L gas engine only needs 87 also but again, designed for work not performance.

 

[petethepug]

A lot of the e85 crowd around here install alcohol sensors in the fuel line then and run a mix of Reg 87 & e85 until they get 95 octane.

The goal is 95 octane petrol based fuel for a racing tune, but the unintended effect is a blend of less expensive regular and even less expensive e85 or .. cheap racing fuel

 

[Marky Dissod]

designed for work not performance

This phrase makes me throw up in my mouth.
'Work' weighs more than 'Performance'? 'Work' uses less throttle than 'Performance'

If GM wanted to, they could write the 6.2L tables PROPERLY, lower the advertised peak ratings a bit, and have far fewer broken Gen4 6.2L engines.
Guess it makes the 6.2L look more like a prestige item, how many of them were broken by idiots flogging them on 87.

It's EASY to argue that idiots can break things by abusing them idiotically. Underdogs can be dunderdogs.
I just don't want to let GM off the hook for being GM - I still remember the Cimarron.
We'd all be far more impressed with GM if there were more 6.2L V8s around to enjoy.

 

[91RS]

Uhh, ok. You can’t tell the difference between an engine designed for towing (torque, lower compression ratio) and an engine designed for performance (power, higher compression ratio)? They have completely different use purposes, you seem like a smart guy, it shouldn’t be hard to figure out. High compression ratios need premium fuel across all brands. There is a reason different octanes exist and are all sold at the same gas stations. If running the correct fuel in the engine bothers you that much, buy a 5.3L and you can safely run 87 all day.

 

[swathdiver]

The trucks do not calculate the grade of fuel and run an appropriate table. The computer advances the timing until it detects knock or pre-ignition and then it pulls timing. Rinse and repeat accelerating from every traffic light, on-ramp and passing a car on the highway, etc..

Our trucks are so well insulated and we're so far removed from the engine that you'll rarely, if ever, hear the motor knock. You fellas running 87, I challenge you to set up your OBDII adapter and app on your phone to display the timing, knock and knock retard.

As for me and my house, all of my Gen IV LS engines run 93 or E85. Even my lawn mower, generator, chainsaw and edger runs fantastic on 93 as well.

 

[swathdiver]

I just don't want to let GM off the hook for being GM - I still remember the Cimarron.

What was wrong with a Caddy Cavalier?

Love my 6.2s, they put a smile on my face every time we get behind the wheel!

 

[Marky Dissod]

You can’t tell the difference between an engine designed for towing (torque, lower compression ratio),
and an engine designed for performance (power, higher compression ratio)?
They have completely different use purposes, you seem like a smart guy, it shouldn’t be hard to figure out.
High compression ratios need premium fuel across all brands.

There is a reason different octanes exist and are all sold at the same gas stations.

TODAY, the reason is because GM failed to write the Low Octane table properly,
and lower the peak ratings as a consequence of using 87.

You're likely smarter than I. It's not as simple as me disagreeing with any of you.
I get why it would be harder to consider the possibility of writing ignition table expecting lower octane to protect an engine,
than to just use 91 or 93.

The trucks do not calculate the grade of fuel and run
an appropriate table.
The computer advances the timing until it detects knock or pre-ignition, and then it pulls timing.
Rinse and repeat accelerating from every traffic light, on-ramp and passing a car on the highway, etc.

Every pcm since the LS1 pcm has TWO ignition timing tables - Low Octane and High Octane -
not AN appropriate table.
However, the pcm interpolates between the two tables essentially as you say it does.
In other words, if the Low Octane Table does not go low enough, or the High Octane table goes too high - OR BOTH -
then the engine cannot run safely on 87 unless the driver is a featherfoot.

If either or both spark tables had been written properly by GM in the first place,
every 6.2L would be able to safely utilize 87, albeit at reduced power.

 

[swathdiver]

TODAY, the reason is because GM failed to write the Low Octane table properly,
and lower the peak ratings as a consequence of using 87.

You're likely smarter than I. It's not as simple as me disagreeing with any of you.
I get why it would be harder to consider the possibility of writing ignition table expecting lower octane to protect an engine,
than to just use 91 or 93.Every pcm since the LS1 pcm has TWO ignition timing tables - Low Octane and High Octane -
not AN appropriate table.
However, the pcm interpolates between the two tables essentially as you say it does.
In other words, if the Low Octane Table does not go low enough, or the High Octane table goes too high - OR BOTH -
then the engine cannot run safely on 87 unless the driver is a featherfoot.

If either or both spark tables had been written properly by GM in the first place,
every 6.2L would be able to safely utilize 87, albeit at reduced power.

I don't think those old computers had the ability to do that. We've only recently seen Toyota and Ram if memory serves do that with some of their vehicles.

I'm aware of the tables, sort of, I thought there was one for gas and one for E85 on the 900s.

To my way of thinking, there would have to be some kind of sensor to detect the octane rating of the fuel and then run the appropriate table.

Maybe they could have written a program to permanently pull timing if there was so much knock retard under such and such conditions and not reset until a refueling event was detected. I would think that all that work would slow down the responsiveness of the system and possibly the engine's reaction to such changing conditions. Just speculating, I'm no automotive software engineer but did stay at a Holiday Inn Express once or twice!

 

[Bagherra]

So if i use 91 or 93 will i notice a significant increase in power over 87??