EFI Fuel Systems – The Basics:
Fuel delivery seems pretty simple in concept, get the gas to the engine. However, with modern EFI engines and the ever increasing horsepower requirement, they can become quite complex while still remain civil enough for everyday use.
The basics for non-direct injection engines include:
- Fuel tank
- Fuel pump
- Fuel pressure regulation system.
- Transfer lines
- Fuel rails
- Fuel injectors.
Anyone that has installed a full EFI fuel system knows that list is far short on details, but we’re only talking basics. We’re also going to shy away from some of the items in the list since the pump is the primary working device and the troublesome part for most builds.
Let’s use a 2000 model year V8 LS1 Camaro as an example. At the time it was considered a pretty powerful car with a rated 320hp. It was, and still is, a fun car. But today 320hp can be had in many V6 engines, and C7 Z06 cars are more than double! Plus, with the supercharged LT4 engine, the fuel requirement from the LS1 Camaro to the C7 Z06 is 2.5 times greater. In other words, the fuel system has to become much more powerful while providing long-term reliability, meet OE requirements for NVH, and be something the owner does not even think about.
Now apply those same criteria to a 400hp LS engine. Multiply the power output by 2.5 = 1000hp. Now run that engine at wide open throttle continuously. Is it going to live, be quiet, out of mind, etc.? Let’s set that aside for a moment…..
So the questions becomes how can a fuel system have a dual personality? For cruise very little fuel is used, but in a traditional return style pressure regulation system that big screaming pump running at full speed is only sending a tiny fraction of that fuel to the engine. The rest is returned to the fuel tank, now heated up by the pump and possibly the engine. Fuel pumps are only roughly 1/3 efficient, so 2/3 of the power gets turned into heat no matter what, and all of it goes into the fuel load. Bigger pump = more heat generation.
Using the 1000hp engine again as an example, is having the engine turning out 1000hp while cruising make sense? Nope, that is why there is a throttle. The throttle restricts the amount of air into the engine. Modern fuel system control strategies perform a similar function, but instead of throttling the fuel pump with a valve, it gets turned on and off very quickly. This makes the large pump act like a small one. The process that performs this function is called Pulse Width Modulation which will be discussed in a following section.