sorry, may be a newbie question, but what is injector slope, and how does it help the performance of your truck, thankx

jared

 

Never heard of it.

 

I think what you've heard about is mostly a f-body thing. Basicly, They don't have a vacuum referenced fuel pressure regulator so there injector flow rate table has to be sloped to accommodate the change in air pressure form vac to wot in the intake. Most trucks have a vac ref fuel pressure reg that changes the fuel pressure in accordance with the vac in the intake, so there IFR table is a flat line. I hope that makes since.

 

The newer trucks with the returnless fuel system have the fuel pressure regulator in the tank and there is no boost reference. The regulated pressure remains constant(although there is also some line pressure drop due to the distance between the regulator and the fuel rails). The effective fuel pressure, which is based on the pressure differential between the fuel rail and intake ends of the injectors, therefore varies with manifold vacuum or boost. For tuning purposes, the proper injector flow rates should be entered in the IFR vs Manifold Vacuum table. The PCM uses this information to determine the injector duty cycle necessary to provide the proper amount of fuel. If you enter the actual IFRs, then the line should be sloped for this type of fuel system.

One way to adjust the fuel mixture(during open loop conditions) in either system is to modify the IFR values in the table. Hence, changing the slope of the plot. For example, if you enter a higher value than the injector's actual flow rate, then the PCM reduces the injector duty cycle accordingly causing the AFR to go leaner. That is, there will be less fuel delivered to the cylinders than what the PCM thinks there is.