Do yall use regular or mid grade gas in the 5.3?

[Burban22]

2003 suburban 5.3 LM7. 165k and it runs great! Sent all fuel injectors off and had them ultrasonic cleaned and they replaced the strainer baskets on each injector. Fuel trims look good now but can only get 15-16 at 70-75. Maybe it’s the 33” K02 tires because I pulled down 18-19 with the stock tire size going 70.

Is it worth paying 60-80 cents more per gallon for 91 high octane? The burb is Blackbear tuned but I’ve only ever run 87. Anyone notice a mpg improvement?

In my 2018 6.2 L86 I definitely see a mpg increase running 91 vs 87 and that engine recommends 91 since it’s higher compression ratio.

 

[Marky Dissod]

Is it worth paying 60-80 cents more per gallon for 91 octane?
The burb is Blackbear tuned, but I’ve only ever run 87. Anyone notice a MpG improvement?

Is it worth paying about $20 per tank more, for 91 octane? Is it tuned FOR 91 octane? ('cause you left that out, or forgot, or something)
If yes, then yes of course. If not, then no, you won't see an MpG improvement.

In my 2018 6.2L L86 I definitely see a MpG increase running 91 vs 87, and that engine recommends 91 since it’s higher compression ratio.

It recommends 91 because GM tuned the ecm to take advantage of the higher static compression ratio, not just for the static compression ratio alone.
How quickly y'all forgot about the '07 Denali's L92 peak power rating on 87, vs the '07 Escalade's L92 on 91. OK, it's been 20 years, but still ...

 

[Marky Dissod]

Bad news for those who believe in 91 or 93, at least in NYC:

96% of NYC Gas Stations Tested Failed Inspection, Primarily Due to Wrong Octane Numbers: Report

702 out of 729 stations tested by the Department of Consumer and Worker Protection reportedly flunked at least one inspection between 2023 and 2025.

www.caranddriver.com

One more reason to tune for 87 octane ...

 

[RST Dana]

1 reason that happens is because the 1st station can not fit the amount that was estimated the station needs.
So when the remainder does not fit in the tank, the driver lets the dispatcher know how much fuel is remaining. The dispatcher then lets the driver know where to take the remaining fuel. Typically a non branded station.
A non branded station when buying fuel directly gets the same gas as everyone else without an additive package, making it just plan gas without an additive package.
When the delivery driver loads the fuel it becomes branded with the additive package Conoco, Exxon or what ever brand.
A non branded station could be fueled with Conoco, Exxon, Shell or whoever and all mixed together.

That may be true today, but not as recent as 2002 when we sold out fuel supply company. We purchased the same gas/diesel as chevron and it was delivered in one of our none branded tankers. Additives were already on board when it was loaded at the terminal for EVERY truck.

 

[SpareParts]

Last i was in that game was about 2000.
When our drivers loaded at the refinery all the fuel started out the same. When loading the additive package was added for what ever brand fuel was needed.
A non branded station gets fuel out of the same tanks as everyone else but no additive package was added.
Knowing how a refinery works i do not know how a non branded station would even been able to load a branded fuel.
I suppose i could see a refinery owned by a name brand allowing a non branded truck to load without the additive package.

 

[tom3]

Interesting write up on the octane rip off deal. From making 5 cents a gallon the probably foreign owned station goes to 95 cents a gallon at the end of the day. In our small town there's one remaining station/mart type store that's not foreign owned. That's a Speedway station.

 

[Marky Dissod]

Bad news for those who believe in 91 or 93, at least in NYC:

96% of NYC Gas Stations Tested Failed Inspection, Primarily Due to Wrong Octane Numbers: Report

702 out of 729 stations tested by the Department of Consumer and Worker Protection reportedly flunked at least one inspection between 2023 and 2025.

www.caranddriver.com

One more reason to tune for 87 octane ...

Interesting write up on the octane rip off deal. From making 5 cents a gallon the probably foreign owned station goes to 95 cents a gallon at the end of the day.

Not saying that anyone WANTS to do this, but this'd be reason enough for me to DEtune a 6.2L's spark maps for 87 octane.

 

[LSCALADE]

I run 87, but shortly after I got mine I installed the missing GM FLEX FUEL sensor, the wiring was there all I had to do was plug it in and copy the FF tables from a 2015 suburban into mine. Now it runs on any mix of 87 and E85. The beauty is at 30% flex fuel the equivalent octane is about 93 so its a cheap way to make 93 without the cost.

The Plus side is it cools the combustion chamber which helps with those high summer heat days and towing. The bad if there is any is that you may loose MPGs however, in my testing I actually get better MPG with 20-30% Ethanol mixed vs straight 87. The upgrade was about 90% and has paid for itself already.

 

[fondupot]

87 for me in my 2021 5.3. Occasionally I'll put some ethanol free in, its usually 89 or 90 octane. But that's rare.

 

[jaxscuby]

so went back to 87 for last 3~4 tanks of gas.
Hear pinging under 1/2 to 3/4 throttle in flat florida.

so back to 89..

 

[Marky Dissod]

so went back to 87 for last 3~4 tanks of gas.
Hear pinging under 1/2 to 3/4 throttle in flat florida.
so back to 89 ...

Either you need new plugs or wires or coils (alone, or in combination), OR ...
What if you paid 87 octane prices, but got subpar/schidty less-than-87 octane 'gas'?
No matter what, SOMETHING is wrong.

 

[jaxscuby]

So I work on military base and get my gas usually there.
Yes swapped plugs & wires recently. no mis-fire cdoes.

just heard pinging and went back to 89..no more pinging..