In the above that the injector data stayed the same, but we adjusted the Actual System Pressure to 60 psi. Notice how this affected Total Injector Flow (now 70.9 lbs/hr) and Total System Fuel Flow (now 567 lbs/hr)? This is a big difference from the prior setting; 87 lbs/hr of additional calculated fuel flow can support an additional 170 hp. Needless to say, if you were working with these incorrect values, the fuel mapping would be way off. If the fuel mapping is set using these incorrect values, any changes made to the system down the road would be tedious at best. If you enter the fuel injector and fuel system values correctly, any future changes to the injectors or fuel system are easily dealt with as you only need to adjust these constants rather than having to go back and re-map the entire fuel table. One other variable you must lend consideration to is that of varying fuel pressure. If the fuel pump in the vehicle is at or near its fuel flow limit, you may find that fuel pressure drops as fuel demand increases. This isn't good as it can cause a lean running condition and possibly catastrophic engine damage. The solution is to verify the fuel pressure and be certain that the fuel pump can meet the demands placed on it. If it can't, upgrade the fuel pump and verify proper system pressure during all engine operating conditions. This way you only have to calibrate the fuel map once and can then enjoy the ride.
This is a common mistake that stems from a misunderstanding of EFI systems and their capabilities. It must be recognized and understood that the ECU simply can't make up for any and all environmental conditions that exist when the engine is being tuned. This being the case, be mindful of the equipment you are using, the data you see, and then use logic to determine whether or not what you see makes sense.
To understand how things can go wrong, begin by considering what the ECU is designed to do. The intent of Auto-Tuning is to make the task of fuel mapping simpler and quicker. The ECU reads the O2 sensor signal to determine how rich or lean the engine is running and then adjusts the fuel delivery accordingly. This is a closed-loop feedback function. It works great if everything is perfect. The trick is to make sure that what the ECU "sees" is what's actually happening. A few examples of things that can go wrong:
- Fuel that is of poor quality and/or contaminated: Will the O2 read correctly? Probably not. Logical fix: Use fresh fuel of high quality. Better yet, use the exact type, brand and octane of fuel when tuning that you intend on using all of the time. This will help ensure proper fuel mapping.
The injectors indicated above are 60 lb Deka IV injectors manufactured by Siemens. It's selected from the drop-down menu (again, convenient!) However, there may be a difference with how the vehicle is mechanically set up. The fuel pressure regulator in the vehicle may not be set to a standard or any specific value, and this can make a huge difference! Selecting the correct fuel injector from a drop-down menu may not be enough. If you have custom injectors, enter the appropriate values in all of the above parameters; they're usually readily available from the vendor. Once you have the correct values in place, verify the fuel pressure at the fuel rail on the engine. Then go back into the above section and double check that the Actual System Pressure matches. Take a look at the screen-shot below:
The Base Timing Table above has 34 degrees of ignition advance programmed into it at WOT at 1-bar manifold pressure, from 4,000-6,000 RPM. It's circled in red above. The math is pretty simple. If you have 34 degrees of timing commanded by the ECU and the mechanical advance allows another 25 degrees of advance, the answer is KABOOM!, or 59 degrees of advance in numeric terms. I promise you; the engine won't hold together and it'll conveniently fit in a bucket so that you can carry it home. When installing an EFI system on an engine equipped with a distributor, ALWAYS USE A FULLY LOCKED DISTRIBUTOR. No vacuum or mechanical advance. Locked. Period. Two down, three to go...
Almost all EFI systems require you to program in some fuel injector parameters. Some systems are very basic, others more complex. The Holley Dominator offers drop-down menu options to make your life easy, but if you have a custom set of injectors, you can enter specific values, offsets, etc as needed. In the screen-shot below, you can see that we've highlighted 4 specific parameters. Under Fuel System, we've highlighted Actual System Pressure and Total System Fuel Flow (a calculated value). Under Injector Set 1, we've highlighted Rated Flow per Injector along with Rated Injector Pressure as well as Total Injector Flow.