Timing/Octane question

[Stu_486Fitter]

I read in a previous post http://forum.gopowerhungry.com/2004-...-program.html? that if you are running an octane level other than the one specified for a tune you should retard/advance timing. Im kind of clear on it but just want to be sure. Im running 87t canned tune but always run 93 octane. BTW its a 06 5.4 if it makes a difference

[Jackpine]

First, I have to ask: "Why are you using the 87t tune if you're burning 93 octane gas. Are you towing?" If so, then yes - go ahead and advance the timing. You should be able to set it to +3, but I'd start with +2, since your engine is most always "under load" when towing. If you notice no problems, try setting it higher, to +2.5, then +2.75 and finally to +3.0 if things seem OK.

If you're NOT towing, you should really be using the level 3 91+ octane canned tune. In that tune, with 93 octane gas you MAY be able to set the timing to +1, but I'd do it in stages (+0.5, +0.75, +1.0), checking for problems at each step.

- Jack

[Stu_486Fitter]

Sorry. Probally should have been more specific. Using 87t because i am waiting on custom tunes and have a CAI. Have recently switched to 93 because it was having issues(prior to tunes) and the higher octane seemed to help

[Jackpine]

What issues? If you're having issues at stock, don't expect canned or custom tunes to fix them.

- Jack

[Stu_486Fitter]

Not expecting tunes to fix. At WOT with 87 octane the motor would break up a lil bit and the CEL would flash as if it was a miss but wouldnt record a fault. Was suggested to me to use a higher quality fuel with a higher octane, and it runs beautifully now. Note: that was happening AND was cleared up before the tuner was ever in play. Now I always run 93 and want tuner adjusted accordingly untill i receive my custom tunes.

[Jackpine]

No - You're not understanding what I meant. Your truck was designed to run on 87 octane gas. It should do that just fine as long as there's no underlying problem. Fixing it by burning 93 octane gas is like putting a bandaid on an oozing sore - the infection's still there, but you don't see it.

Why did you get a power loss at WOT? Just a guess, but perhaps you hit the rev limiter - which causes an immediate "cut out" to prevent damage. Why don't you get this using 93 octane? You might, if you advance the spark to take advantage of the anti-knock properties of the fuel. Right now, your spark is retarded for the fuel you are using and you probably develop LESS power at a given throttle setting/load than you did using the 87 octane gas. This means the truck will not pull as "hard" as it did with 87 octane, since the "burn" is not coming at an "optimum" time in the piston's power stroke.

- Jack

[Stu_486Fitter]

It wasnt the rev limiter. Like i had said it felt as if it was missing..but it was NOT all the time. Just sometimes when I would drop into passing gear. Truck would be warmed up so i know it wasnt the usual break up from a cold engine.

I just got back from running it with the timing advanced 2.5* and it ran fine across the board. Just a touch more "ummph".

Back to the said issue...was going to do plugs until my mech. buddy caught me with a socket in hand and told me to STOP. I didnt know then of the lovely spark plug phenomenon of the 3v's. Thought to myself it could either be a fouled plug missing or a bad coil..but after speaking to a few people i personally ruled those out because it was intermittent....then came the octane switch and i havent seen it since

[Stu_486Fitter]

Oh yeah and I forgot to say we tried to read the CEL to see if it actually WAS a miss but nothing was stored in memory. Kind of makes it tough to diagnose...but this was all happening almost 6+ months ago

[ticopowell]

IMHO I think it would be best to go back to 87 octane, or try the 93 octane tune to see if it happens again. If it doesn't then you are probably going to be fine with a custom tune, but if it does I would get the problem fixed before possibly making it worse by doing a custom tune. just my 2 cents

[Jackpine]

Going back to 87 octane gas is a good suggestion, but with the CAI, I'd stay away from the Level 3 tune until you get a custom tune designed for that combination.

Actually, though, with a commercial CAI, you should not be doing any WOT runs until you DO get a custom tune. Those things are not going to give your engine a correct A/F mixture at WOT and you risk causing damage due to the mixture being too lean, which could also cause a "miss".

- Jack