ECU/EFI adjustments Trail versus HWY
Posted: Sun Sep 04, 2016 7:41 pm
If your running with EFI, you may be leaving up to 20% of your potential torque on the table.
There is a trade off between fuel economy and power -- basically HWY versus the trail.
After a lot of experimentation, I have finally dialed in a decent recipe -- and yes, I had been
leaving unexploited torque under the Dog house. The fix turns out to be simple, run richer
at low RPM -- better torque and no hesitation.
What I have noticed is that between 1,000 to 2,000 RPM torque was poor with hesitation.
Above 2,000 RPM, nice and smooth. But with the TD Tranie in a 710K, 2,000 RPM is a
race walk not a crawl -- which can be dangerous on step grades with obstacles.
It has bugged me that with 2.7L/EFI, with supposedly more torque across the entire RPM
range, I should be able to crank at a lower RPM than a stock Pinz compensating for the
gearing in the TD tranie -- this hasn't been the case at all. To get there I need to run strong,
at load, below 2,000 RPM.
The fix was simple. Run a richer fuel mix at low RPM, and VERY important -- turn OFF
Closed-Loop operation on the ECU. The target AFR for peak torque is 12:1, for fuel
economy it is 14.7:1 which will be at the expense of power -- up to 25% less.
That did it, smooth and increased Torque from 1,000 to 2,000 and no hesitation.
The ECU's Closed-Loop feature attempts to maintain a Stoichiometric condition in the burn; as
perfect as possible conversion of Octane to CO2+H2O which results in best fuel economy. The ECU
table values set the base-line for the amount of Fuel to inject at a given RPM and Manifold Pressure.
Then Closed-Loop will increase (or decrease) that amount to get as close to 14.7:1 as possible. Most
ECU's limit the amount of tweaking to 10% to 20% of the table value, but that's sufficent to mess things
up. The key point is if Closed-Loop is ON it works hard to get better fuel economy thus defeating best
possible power.
If you had your ECU tuned by someone thinking economy was important, or high RPM is normal
operation you may have less than optimal values set in your tables and you may have Closed-Loop ON.
It was pretty easy for me to tune in AFR as I can monitor AFR and MAP and adjust accordingly.
Looking at AFR going up steep grades. The RPM range of interest is 1,000 to 3,000 RPM. Some ECU's
are very simple to adjust. Ones with 2-dimensional or 3-dimensional tables are a wee bit harder. My
unit is a SDS EM4 which supports an external AFR meter and has a fuel adjustment knob so I can
increase/decrease the baseline amount of Fuel versus RPM on the fly.
For the trail, I will have the fuel adj. knob set +15% for 12:1, and near 0% for a HWY AFR of 13.5:1.
It would be nice to have a switch or programming feature to load a table for trail or HWY which is
not supported on my ECU.
This has made a huge difference in my low end power, you might want to take a look at your setup
if you haven't already.
There is a trade off between fuel economy and power -- basically HWY versus the trail.
After a lot of experimentation, I have finally dialed in a decent recipe -- and yes, I had been
leaving unexploited torque under the Dog house. The fix turns out to be simple, run richer
at low RPM -- better torque and no hesitation.
What I have noticed is that between 1,000 to 2,000 RPM torque was poor with hesitation.
Above 2,000 RPM, nice and smooth. But with the TD Tranie in a 710K, 2,000 RPM is a
race walk not a crawl -- which can be dangerous on step grades with obstacles.
It has bugged me that with 2.7L/EFI, with supposedly more torque across the entire RPM
range, I should be able to crank at a lower RPM than a stock Pinz compensating for the
gearing in the TD tranie -- this hasn't been the case at all. To get there I need to run strong,
at load, below 2,000 RPM.
The fix was simple. Run a richer fuel mix at low RPM, and VERY important -- turn OFF
Closed-Loop operation on the ECU. The target AFR for peak torque is 12:1, for fuel
economy it is 14.7:1 which will be at the expense of power -- up to 25% less.
That did it, smooth and increased Torque from 1,000 to 2,000 and no hesitation.
The ECU's Closed-Loop feature attempts to maintain a Stoichiometric condition in the burn; as
perfect as possible conversion of Octane to CO2+H2O which results in best fuel economy. The ECU
table values set the base-line for the amount of Fuel to inject at a given RPM and Manifold Pressure.
Then Closed-Loop will increase (or decrease) that amount to get as close to 14.7:1 as possible. Most
ECU's limit the amount of tweaking to 10% to 20% of the table value, but that's sufficent to mess things
up. The key point is if Closed-Loop is ON it works hard to get better fuel economy thus defeating best
possible power.
If you had your ECU tuned by someone thinking economy was important, or high RPM is normal
operation you may have less than optimal values set in your tables and you may have Closed-Loop ON.
It was pretty easy for me to tune in AFR as I can monitor AFR and MAP and adjust accordingly.
Looking at AFR going up steep grades. The RPM range of interest is 1,000 to 3,000 RPM. Some ECU's
are very simple to adjust. Ones with 2-dimensional or 3-dimensional tables are a wee bit harder. My
unit is a SDS EM4 which supports an external AFR meter and has a fuel adjustment knob so I can
increase/decrease the baseline amount of Fuel versus RPM on the fly.
For the trail, I will have the fuel adj. knob set +15% for 12:1, and near 0% for a HWY AFR of 13.5:1.
It would be nice to have a switch or programming feature to load a table for trail or HWY which is
not supported on my ECU.
This has made a huge difference in my low end power, you might want to take a look at your setup
if you haven't already.