Injectors
Injector Color Codes
You can use different injectors in the fuel rail and plug them into the harness, but there may be additional problems that you may not have considered or even known could occur.
Injectors take time to open; they do not open instantly in 0 seconds. The standard opening time is 1-3ms (milliseconds) in most cases. Because the injectors are not flowing 100% while opening you can flow different amounts at different duty cycles. If you open an injector for 20ms, it will flow a specific amount of fuel. Open it for 10ms, it will flow a little less than half that much fuel. Open the injector for 1ms, you would assume it would flow 1/20th as much. BUT it actually flows much less than 1/20th because it never fully opened.
Understand that?
Say an injector takes 2ms to open, and EEC is at the 2ms duty cycle. During those two milliseconds it flowed something, but as much less than it's full potential because it never actually opened 100%. If you open that injector for 4ms duty cycle, the natural assumption would be that the injector would flow twice as much as than the two milliseconds duty cycle. But it actually flows a lot more fuel at 4ms duty cycle because is spent 2ms at 100% fully open. Hence, opening it 4 milliseconds causes it to flow more than twice as much as opening it 2ms. As a result, injectors don't actually supply fuel to an engine in a linear pattern we can program into the EEC.
This non-linearity fuel flow is called “Injector Slope." The EEC-IV has a parameter for compensating for injector slope programmed within.
Injectors are basically little valves operated by an electromagnet. The size of the electromagnet determines how much electrical power they draw and how much physical work they can do. When they're turned off, the injectors are closed because the fuel pressure and an internal spring keeps them shut. When you turn them on (apply power to them) the electromagnet overcomes the fuel pressure and opens them. The time it take an injector to fully open is depends on how much force there is on the pintle, and the size of that pintle area. Injectors that have higher flow ratings have a larger pintle (valve) in order to flow more fuel. The larger pintle means more surface area. More surface area means the fuel pressure applies more force to it. Remember pressure is pounds per square inch. We have the same force, but more area making it harder to open. This would make the injector open more slowly except they use a larger electromagnet to apply more opening force. So now we know why different flow rating injectors have different “Injector Slopes.”
If the computer is programmed for a specific injector slope and you change injectors, what happens? The EEC runs its program and determines the exact amount of fuel to add to the air. Trust me this gets real accurate, we are talking grams of air per second. Unless you reprogram the computer (with an EPEC, eec-tuner, or AutoLogic chip) to change the injector slope in the program you will cause the injectors to flow an incorrect amount of fuel.
But we can fix this with adjustable fuel pressure regulators, right? NO! You could compensate for this by changing the fuel pressure, but how well are you at altering injector slope with a screwdriver? You’ll end up getting what you think is good idle eventually, but will only make things worse on the rest of the driving conditions.
But that fancy O2 sensor will notice the incorrect A/F ratio and fix it? HA! If you’re expecting a sensor to live in an exhaust pipe in 1000+ degrees and all kinds of pollution and remain 100% accurate, you are stupidly buying the auto industry voodoo magic. If you expect that same sensor to fix your already messed up EFI fuel problems, YOU ARE DUMBER THAN I CAN HELP! If you assumed that the EEC adjusts the A/F ratio all the time with the O2 sensor, remember the O2 sensor is only used in closed loop which is during cruise on the highway. So you will only get the correct A/F ratio at these times
I suggest you leave the injector alone unless you have means to tune it (EPEC or EEC-Tuner, AutoLogic chip) And If your making more than 300HP shouldn’t you be looking for an EFI tuner anyway?