Thread: Fuel Pump

I noticed many people change out there fuel pumps having very few mods. What does that do?

The stock fuel pump can supply enough fuel to the fuel rail to handle stock power levels but once you start pushing more air, you'll need more fuel. The stock fuel pump on DSMs (not sure about Evos) isn't able to provide that fuel and you could run lean just by increasing airflow. If you're seeing it on many evos, it's probably the same case but I'll wait for Rich or Jonothan to confirm that.

So I'm guessing the sensors tell the pump how much fuel it needs or do you just regulate it to what you want it?

Thanks for your response bro.

the MAS sensor (the one connected to the air box) calculates air volume and density, and the ecu adjusts accordingly at the injectors, the o2 sensors also play a part in this


the larger volume pump is part of the ecu being able to match the larger amount of air coming in

Your Evo IX has a bigger fuel pump than an Evo VIII. It allows you to push 20psi stock and is able to hold up to 400whp.
The only reason why people upgrade in the Evo is because of the lower octane we have in CA or if you're just wanting to bump up the boost to anything past 21-22psi. But, it also lets you get ready for adding more serious mods to the car.

Right now... I'm running 23psi and it holds rock steady with no taper or creep. That is on a pretty conservative tune to save my engine life. I'm not running into any lean spots or any other problems.