Adjusting Injector Slope (LTFT) For Highway Fuel Economy

[h2bob]

Hello,
The tutorial states to adjust the injector slope so that LTFT is within the -2 to 0 range. At approximately what AF ratio does this make the car run at part open throttle (cruising)? Can it be checked with U7193 (9r01)? As a slightly rich mixture is for maximum power and slightly lean for maximum fuel economy, would going slightly positive on LTFT give better highway fuel economy? Any other recommended changes to get the best fuel economy (running 87 tune)? Thanks.

[mikel]

The truck will always run at right around 14.75:1 at cruise.

Thanks

[h2bob]

So what is the point in adjusting the injector slope if I keep the stock injectors?

[Grumpy_Aero_Guy]

The injector slope has nothing to do with "what ER is set" ... directly.

The Injector slope is a control parameter that controls how puch fuel gets sprayed at a given electric pulse.

If an injector slope is not zero (which is 99% of the time for 99% of the vehicles), it means that the control is adjusting how much fuel gets injected to achieve 14.7.

If thew IS is a big number (neg or positive) it means the control commands 14.7, and doesn't get close, and the IS then adjusts, or biases, the control to, indeed, achieve the desired 14.7 ER.

The point is, adjusting the slope in the control correctly allows the control to achieve its commanded value with minimal biassing.

[h2bob]

From what I understand, IS is a constant factor in the fuel delivery equation while LTFT is variable. Won't LTFT change to the "needed" value once the vehicle has been driven for a while to correct for the wrong IS value and so it would not really make a big difference if IS is correct?

[06MonteSS]

read this similar/same question and answers - all the answers are there:

http://diablosport.com/index.php?name=P ... pic&t=9013

[h2bob]

Was the same question, sorry. Here is another one. Is it possible to make the PCM go slightly lean when cruising with the possible adjustments using the predator? Would a custom tune be overly complicated?

[06MonteSS]

no, cuz the PCM is then just going to add more fuel back in anyway to get back up to the 14.75 AFR for normal cruising/driving...

the ONLY vehicle I've seen/read about that was able to get a "lean cruise" setup are the 2004 GTO's... which is because those are PCM's from Holden Australia - and their setup is different, allowing that trick to work. Starting with 2005 GTO's, the ECM's are from the US, and that capability is gone. But, like I said, that is the only vehicle I've ever seen/read about that was able to do that tricky setup.

It is not possible on any other vehicles.

and being a Hummer with 31" tires doesn't help any either..

[h2bob]

Sure doesn't . Anyone try skewing O2 output?