Tonyrodz's Tahoe Build Thread

[Tonyrodz]

I’m feeling your pain, Tony. I wish you had a BB tune, Justin would help you figure this out. Sorry for your troubles but I’m no help I’m afraid.

Thx Mark. Funny thing--I bought a used Autocal on here--but I can't find the damn thing now!! The dementia is coming in hard dammit! Sure would come in handy!

 

[Rocket Man]

Thx Mark. Funny thing--I bought a used Autocal on here--but I can't find the damn thing now!! The dementia is coming in hard dammit! Sure would come in handy!

Damn, you need to find it. I think a tune is only about $300 and it would sure be worth it. You could have Justin tune it, troubleshoot your issues, and turn on your Efans. Better start looking harder.

 

[Snowbound]

Called Brian Tooley tech line and asked about compatibility of this cam with the higher compression of the LQ9. He said everything will play nice together. I have a low octane tune so I asked about KR, timing while using 89 or 91 octane. He said since I have a low octane tune I'd be wasting money putting anything over 87 in it. I'd gain 0 benefit.

I don’t like to step on toes very often, especially ones from a reputable source such as BTR. But in this case I want to give my .02 so take it for what it’s worth.
In a N/A engine with a standard compression rating of 9:1, I agree, octane greater than 87-89 is not gonna be worth the benefit. Higher octane the fuel is, the more stable it is. When dealing with higher compression rating such as the LQ9 you have in your Hoe, it’s NOT gonna have a good volumetric efficiency rating with the lower octane fuel. The ECM WILL respond and protect the engine from lower octane by retarding ignition timing both immediately and long term. The result is reduced fuel efficiency (sometimes as high as 3-4mpg) and considerably less power output than would be seen on 91+ octane. You won't notice this power loss under light throttle though due to the ECM's method of controlling throttle angle... essentially, the throttle will be opened more for the same power output target on 87 so that it feels exactly the same to the driver.
In terms of ignition timing, where 18-19 degrees of advance timing might be the target by GM under the factory tuning, on 87 octane, that timing drops to under 10 degrees of advance to prevent knock from occurring (in response to knock that has already occurred). Anybody that has dealt with ignition timing should see this as a very poor situation. The knock retard occurs early and quickly and then the lasting effects (octane scaler blending the high and low octane tables) will stay in effect for dozens of miles before decaying out. This is the reason why people say they put 91+ in and didn’t see or feel a difference. It takes a few tanks before the timing tables scale out and the benefits are noticeable.
Here’s a real life experience. Buddy has a K2500 with the 6.0. Said he was getting 15.2-15.6 MPG consistently. Switched to 91 and 2 weeks later he was seeing 18.7-19.2 MPG.
Take it for what it is. If the octane rating didn’t do anything they wouldn’t require it in these high compression engines. What is the cost saving from 87 to 91? Right now 87 is $2.25 and 91 is $2.97. This is a Shell station near me. That’s $0.72/gal difference. So let’s say it takes 25 gallons to fill up. That’s $18.00 more. Using my buddy’s numbers just for numbers sake. 87 octane at $2.25/ gal and 25 gallons he pays $56.25 to fill up. Now he only gets 15.4 MPG average. So he will go 385 miles on that tank. 91 octane at $2.97/gal and 25 gallons is $74.25 to fill up with 25 gallons. He will now go 472.5 miles on that same 25 gallons at 18.9 MPG average. He went 87.5 miles further on that tank. So mathematically that $18 in higher fuel cost only cost him just shy of $5 because he went further not to mention had more power and burned cleaner while doing so.
IMHO, it costs more not to fill up with premium. And that’s all I’m gonna say about it.


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[Dantheman1540]

I don’t like to step on toes very often, especially ones from a reputable source such as BTR. But in this case I want to give my .02 so take it for what it’s worth.
In a N/A engine with a standard compression rating of 9:1, I agree, octane greater than 87-89 is not gonna be worth the benefit. Higher octane the fuel is, the more stable it is. When dealing with higher compression rating such as the LQ9 you have in your Hoe, it’s NOT gonna have a good volumetric efficiency rating with the lower octane fuel. The ECM WILL respond and protect the engine from lower octane by retarding ignition timing both immediately and long term. The result is reduced fuel efficiency (sometimes as high as 3-4mpg) and considerably less power output than would be seen on 91+ octane. You won't notice this power loss under light throttle though due to the ECM's method of controlling throttle angle... essentially, the throttle will be opened more for the same power output target on 87 so that it feels exactly the same to the driver.
In terms of ignition timing, where 18-19 degrees of advance timing might be the target by GM under the factory tuning, on 87 octane, that timing drops to under 10 degrees of advance to prevent knock from occurring (in response to knock that has already occurred). Anybody that has dealt with ignition timing should see this as a very poor situation. The knock retard occurs early and quickly and then the lasting effects (octane scaler blending the high and low octane tables) will stay in effect for dozens of miles before decaying out. This is the reason why people say they put 91+ in and didn’t see or feel a difference. It takes a few tanks before the timing tables scale out and the benefits are noticeable.
Here’s a real life experience. Buddy has a K2500 with the 6.0. Said he was getting 15.2-15.6 MPG consistently. Switched to 91 and 2 weeks later he was seeing 18.7-19.2 MPG.
Take it for what it is. If the octane rating didn’t do anything they wouldn’t require it in these high compression engines. What is the cost saving from 87 to 91? Right now 87 is $2.25 and 91 is $2.97. This is a Shell station near me. That’s $0.72/gal difference. So let’s say it takes 25 gallons to fill up. That’s $18.00 more. Using my buddy’s numbers just for numbers sake. 87 octane at $2.25/ gal and 25 gallons he pays $56.25 to fill up. Now he only gets 15.4 MPG average. So he will go 385 miles on that tank. 91 octane at $2.97/gal and 25 gallons is $74.25 to fill up with 25 gallons. He will now go 472.5 miles on that same 25 gallons at 18.9 MPG average. He went 87.5 miles further on that tank. So mathematically that $18 in higher fuel cost only cost him just shy of $5 because he went further not to mention had more power and burned cleaner while doing so.
IMHO, it costs more not to fill up with premium. And that’s all I’m gonna say about it.


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Very well put and I totally agree. One of the big problems is we don't have any idea what the previous tuner did in his "Low octane tune" Maybe he copied the low octane table onto the high table? The sputtering and strange sounds from the exhaust definitely sounds a lot like the timing is off, I've seen the ecu pull so much timing due to false knock that it dropped to -* which is dangerous.

It certainly wouldn't hurt to start blending in 91-93 and even dump a bottle of octane boost in to see if it makes a difference.

 

[mikeyss]

I only run 91 in my 06 LQ9 S.D., and I average 16mpg combined, but mostly city driving. I don't think that's too bad for it being AWD and having 4.10 gears. Higher compression engines should run better gas.

 

[pwtr02ss]

I was going to say, it sounds like its pulling timing from sensing spark knock from the lower octane. Put some octane boost in the fuel and drive around for a bit and see if that helps. IMO, you need to run whatever high octane is in your area. For me, that's 93. As the others have said, no idea what the tuner did so its very hard to diagnose.

Being as you had a LQ4 before, the LQ9 is a different animal

 

[Tonyrodz]

I believe and trust you guys more then I do them. Makes total sense Jim when you break it down like that.
High octane it is.

 

[Snowbound]

Very well put and I totally agree. One of the big problems is we don't have any idea what the previous tuner did in his "Low octane tune" Maybe he copied the low octane table onto the high table? The sputtering and strange sounds from the exhaust definitely sounds a lot like the timing is off, I've seen the ecu pull so much timing due to false knock that it dropped to -* which is dangerous.

It certainly wouldn't hurt to start blending in 91-93 and even dump a bottle of octane boost in to see if it makes a difference.

Exactly, we don’t have any idea what his tables look like. But I can 99.99% guarantee it’s not the same tables as the Esky PCM that this engine came from. It’s tuned for the LQ4 and not the LQ9. You should be running premium fuel and have a higher timing table for high octane. I’d bet Tony’s left nut that he’s getting shit fuel mileage and the PCM is pulling timing like mad, especially when you went into WOT. Run premium and FIND THAT AUTOCAL!! You need some PCM tweaking badly.


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[Snowbound]

If I had my laptop at my disposal I would be able to pull up the high and low tables from the LQ4 and compare it to the LQ9 and would bet it’s a noticeable difference from just factory settings.


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[Snowbound]

Called Brian Tooley tech line and asked about compatibility of this cam with the higher compression of the LQ9. He said everything will play nice together. I have a low octane tune so I asked about KR, timing while using 89 or 91 octane. He said since I have a low octane tune I'd be wasting money putting anything over 87 in it. I'd gain 0 benefit.

Reading this again I see what BTR was saying. You won’t benefit from higher octane if you don’t have the high octane table set up in the program. This is true. BUT, it will keep it from pulling timing due to running low octane and sensing knocks. So theoretically, you will never get optimized timing without setting up your tune but you will run better and at least keep the knocks down.


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