Tuning and Octane.

[coleflo]

So, lets say I am running a 93 octane tune, and without realizing it I inadvertently pump the truck with 89.

Will the truck just run like crap from the knock sensors doing their job, or is the risk of doing serious damage to the engine a strong possibility?

I guess what I'm asking is how reliable are the knock sensors as a safety net?

 

[Ratket]

is it a 93 octane canned tune or custome tune.. I am sure a canned tune would be fine.. but a custom tune u may hurt something. Canned tunes are just that.. " can oh ****" wouldn't matter what grade of fuel u ran. A custom tune .. well that's to maximize performance.. and may have ur knock sensors turned off.

 

[Hemi450hp]

If your knock sensors work, then the truck will just lose power because of a lot of pulled timing. Truck would likely run slower than stock, but I doubt it would actually hurt your truck though.

 

[coleflo]

I know the custom tuners usually make the KS's less sensitive, but didn't think they completely disabled them.

 

[Hemi450hp]

No competent tuner would completely disable someone's knock sensors unless that someone signed a disclaimer saying they could care less if the motor blows.

With functioning sensors, you wont have anything to worry about aside from the truck running much slower than it should.

 

[Ratket]

when I said turned off I also meant turned down. sorry for mis speaking.

 

[charonblk07]

If you ever run a lower grade of fuel you'll have knock and the PCM will pull timing to compensate. Down side will be that your computer will learn long term knock if it lasts a while which will need an adaptive reset, just fill up with 93 as soon as you can and reset the PCM. Also, try not to push the vehicle too hard if you're modded.

 

[coleflo]

Thanks everyone.

This is pretty much what I thought.

I just started wondering about this when I let my wife take my truck (for the 1st/last.. time/emergency situation ) and told her she needed to stop and get gas. MAKE SURE YOU USE 93!!

Wonder if she really did. Should have made her bring back the receipt.

 

[MADDOG]

Had that happen with my MegaCab.

I was running a canned 91 octane tune. The youngest daughter and her husband borrowed the truck to haul some gym gear and, thinking they were helping, filled it with 87.

I just avoided running at WOT until I had about 1/2 a tank gone, then I topped it off with 92 octane fuel.

I wasn't really worried about harming the engine as I knew KS still worked but I just decided to not tempt fate.

 

[drittal]

Can't you just dump some octane boost in the tank to ease your worries???

 

[coleflo]

Can't you just dump some octane boost in the tank to ease your worries???

Yeah, but I just re-flashed it to the 87 tune to be safe.

 

[coleflo]

Desensitizing knock sensors is just to eliminate background noise that the sensors interpreted as knock.

The bad, often times the background noise or false knock is so loud that the sensors would need to be desensitized to a dangerous level to eliminate it. Which would cause a issue if someone ran a bad tank or lower grade fuel.

Some trucks are plauged with this more then others and the users willingness to search high and low for the source often is key.

Canned tunes in general for the 4th Gen have the sensors set so safe you could litterly run 87 with a 93 tune. But don't recommend it.

For 10 years I ran 93 on a superchips 91 tune to leave a little room for error.

Sounds like I wasted some money seeing how 91 is 10-15 cents a gallon cheaper than 93 here.

 

[coleflo]

Actually the 91 spark on Superchips is pretty aggressive for 3rd gens as compared to the 93 octane Diablo.

My guess is Superchips theory was to let the knock sensors do the work of fine tuning it.

So actually you probably made more power running the 93 since the sensors didn't pull spark.

Does the same apply for most custom tunes as well?

In other words, in hot low altitude climates, Im guessing it would be a good idea to run an octane or two higher than the rated tune ie...89 for 87 tune....93 for 91 tune..exc?

Im also guessing a low T-stat or a catch can would help.