Adjustable parameters explained

05silvycrew · Post by **05silvycrew** » Wed Feb 25, 2009 6:56 pm

m8silverado wrote:Okay, okay, okay. I've read this LTFT thing over and over and I don't understand why it says that if the LTFT is positive the PCM is adding fuel. So negate the LTFT to the corresponding number in order to fool the PCM to think it now has smaller injectors to work with in which it nows adds more fuel. Aren't we trying to get rid of fuel in the first place? Is the amount of fuel now being injected actually less because the computer thinks the injector is smaller? But it's not and by injecting more fuel with the so called "smaller injectors" is more fuel than we started with?

never made sense to me either. my truck ran lean with the 87 tune (according to the LTFT's) something like 7%. So by reseting the injector slope down to -7, I believe I'm adding more fuel. So in the same stretch of an hours drive, i've burned more fuel as compared to leaving it at +7%. more fuel per hour over the same distance traveled should mean less MPG. -2 to 0 on the LTFTs might be optimal for power, but could it be that running a little leaner would yield better MPG?

I don't know, all I do know is that with the injector slope set down to -7 it throws the DIC's accuracy WAAAY off. because the computer thinks I'm spraying less fuel than I really am, thus miscalculating the average MPG's.

05silvycrew · Post by **05silvycrew** » Wed Feb 25, 2009 6:59 pm

it also says for a postive LTFT value to subtract from the injector slope "It is also recommended to lean both fuel tables by the same percentage" refering to the adjustment made to the injector slope. Are they talking about the WOT fueling?

So we're making the LTFT's richer by adding fuel. then we lean out the WOT fuel tables? can somebody shed some light on this for me

spikeyjohnso · Post by **spikeyjohnso** » Thu Feb 26, 2009 1:41 pm

I too am waiting for an answer to 05silvycrew questions regarding the fuel trim adjustments and mileage vs. HP.

spikeyjohnso · Post by **spikeyjohnso** » Thu Feb 26, 2009 1:42 pm

I too am waiting for an answer to 05silvycrew questions regarding the fuel trim adjustments and mileage vs. HP.

Post by **06MonteSS** » Thu Feb 26, 2009 2:59 pm

the DIC needs time/miles to get "caught up" after an injector slope change... it will return to being accurate like it was before... just gotta give it time/miles...

don't lean out the PE fueling table for WOT until you've checked your AFR at WOT to see if you indeed need to do that at all... and you can't with your version predator, so I'd just leave it alone, or go to a dyno and have them check it with a wideband for a couple WOT pulls.

for me, once I got my ltft's dialed in, my WOT fueling was also dialed in, with an AFR right around 12.6 at WOT... so no need to adjust anything at all for the PE fueling.

it may SEEM counter-intuitive, but actually, once you get the ltft's dialed in correctly, your mileage will actually go UP...

you won't ever get it to run "leaner" at part throttle, cuz the ECM will constantly be adding additional fuel to keep the AFR at 14.75... if you're afr is too lean, it will dump in extra fuel to richen it up...

CANUCKPREDATOR · Post by **CANUCKPREDATOR** » Thu Feb 26, 2009 3:07 pm

I've never found the DIC to be accurate anyway. When I would calculate actual miles and actual fuel pumped into the tank, I'd be 1.5 to 2 MPG lower on the DIC. And as far as that goes how accurate is the gas station pump too? Was I filling the tank to the same level?

05silvycrew · Post by **05silvycrew** » Thu Feb 26, 2009 10:17 pm

CANUCKPREDATOR wrote:I've never found the DIC to be accurate anyway. When I would calculate actual miles and actual fuel pumped into the tank, I'd be 1.5 to 2 MPG lower on the DIC.

stock my DIC would be off .5-1 MPG. with the LTFTs dialed in, I'm off 1.5-2.5 MPG, (never gets closer than 1.5 MPG). Does look cool to those riding with me who think my truck gets 19 MPG at 70 MPH though, lol.

as to my other concern about WOT fueling, maybe on the adjustment page there should be some clerification, so that someone reading that statement doesn't go out and over-lean their engine out and cause major issues. I know there's already a disclaimer about not being responsible, but the existing direct statements gives the recommendation from diablosport to do it.

08Chevy · Post by **08Chevy** » Wed Jun 17, 2009 6:42 pm

Are we going on the average LTFT shit? I am reading 2 diffrent LTFT banks and

#1 bank- -3.07648%

#2 bank- -2.67331%

So what do I do. I do not understand any of this LFTF shit. I dont know what the abrevations are.

The truck is a 08 silverado with the 5.3

CANUCKPREDATOR · Post by **CANUCKPREDATOR** » Wed Jun 17, 2009 6:47 pm

LTFT=Long Term Fuel Trim
take the two number and average them. 3.0+2.6=5.5/2=2.8
the goal is to get you average in the 0 to -2 range, so you are just out side that range. go in to the tune that you installed and modify the tune. there is a setting for injector slope, move it -2, press esc until it asks to install the tune and install the tune.

08Chevy · Post by **08Chevy** » Wed Jun 17, 2009 6:50 pm

What else do I need to do? What is DOD?

CANUCKPREDATOR · Post by **CANUCKPREDATOR** » Wed Jun 17, 2009 6:53 pm

Displacement on Demand V4 mode your choice if you want to run V8 all the time or not.

08Chevy · Post by **08Chevy** » Wed Jun 17, 2009 7:13 pm

no. I like the v4 mode. What else do I need to adjust to make more power?

08Chevy · Post by **08Chevy** » Wed Jun 17, 2009 7:38 pm

I did the log and what else can I adjust from the specs it gave?

Post by **06MonteSS** » Thu Jun 18, 2009 8:07 am

CANUCKPREDATOR wrote:LTFT=Long Term Fuel Trim
take the two number and average them. 3.0+2.6=5.5/2=2.8
the goal is to get you average in the 0 to -2 range, so you are just out side that range. go in to the tune that you installed and modify the tune. there is a setting for injector slope, move it -2, press esc until it asks to install the tune and install the tune.

NOOOOO...

his average ltft's are already -2 and -3...

need to adjust the injector slope +2%

CANUCKPREDATOR · Post by **CANUCKPREDATOR** » Thu Jun 18, 2009 10:09 am

sorry, looked twice, typed once, my bad