BASICS OF EFI FUEL SYSTEMS

Fuel delivery seems pretty simple in concept: get the gas to the engine.

However, with modern EFI engines and the ever-increasing horsepower requirements, the fuel delivery can become quite complex but still need to remain civil enough for everyday use. Ever hear of a modern OEM 750+ horsepower car off the showroom floor have fuel delivery problems? They must be
on to something.

The basics for a modern OE-type EFI engine components include:

• Fuel tank
• Electric Fuel pump
• Fuel filter
• Fuel pressure regulation system
• Transfer lines
• Direct Injection Pump (DI type engines only)
• 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 electric fuel pump is the
primary working device and the troublesome part for most builds.

Let’s talk numbers:

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 LT4 equipped C7 Z06, Demons, GT500’s, etc. 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 may be something the owner does not even think about.

Now apply those same criteria to a 400hp engine: multiply the power output by 2.5 = 1000hp.

Then, run that engine at wide open throttle continuously. Is it going to live, be quiet, out of mind, etc.?

Setting that aside for a moment…

So the question 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, engine compartment, exhaust, etc.

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 on the engine. The throttle restricts the amount of air into the engine to only what is needed to produce the right-foot enabled power needs.

Modern fuel pumping system control strategies perform a similar function, but instead of throttling the fuel pump with a mechanical valve, it gets turned on and off very quickly. The longer the pump is on, the faster it spins, which can then be sent to the engine. Being thoughtful with that idea, spin the pump just enough to feed the engine, hence making the fuel pump on-demand variable speed.

This makes the large pump act like a small one, just like an engine throttle .

The process that performs this function is called Pulse Width Modulation which will be discussed in a following section.