What's The Difference Between Em?

or the 1995 model year, HarleyDavidson introduced electronic fuel F injection for the first time on certain touring models. The Magneti-Marelli system that was introduced in 1995 saw use until the mid-2001 model year. In 2001 a new system, [Delphi], was introduced on EFI models and is still in use today. 2007 was the last year for carburetion on any Harley-

Davidson motorcycle, and it was only available on certain models. This included the Sportster.

The main difference in these systems is that while the Marelli system is a “return” style system while the later [Delphi] system is a “deadhead” system. For the purpose of this article, we will only gloss over the

Marelli while we will do a deeper dive into the Delphi.

For starters, we need to compare the similarities between these two types of systems. All Harley-

Davidson’s with fuel injection features a fuel pump mounted in the tank.

All HD EFI systems are sequential. (Sequential means that each cylinder 28 December ‘21 - January ‘22 - CYCLE SOURCE MAGAZINE

Article & Photos By: Jason Hallman

has its own dedicated fuel injector) carbureted model. On these models, and both systems require some type one check valve is for feed while the of pressure regulator to manage other is for return. Once the fuel pump the pressure on the inlet side of is initiated, the fuel in this system the fuel injectors. Also, both fuel stays in constant circulation. The injection systems have a throttle maintained pressure required on the body to manage the amount of air feed side of the system is regulated entering the engine and a dedicated by an external pressure regulator. ECM to control all functions relative The fuel that is not consumed by the to timing, fuel and monitor overall engine is simply “returned” to the engine performance. fuel tank, just like the name “Return-

Let’s now examine the differences Style” implies. between these two systems. As we mentioned, the Marelli system is a return system and was employed until mid-2001 on touring models only. The easiest way to identify these systems is by their dual fuel injection check valves on the left side of the tank, where you would normally find a fuel valve on the

Once introduced, the Delphi system made things much better. For starters, there were fewer moving parts. The previous dual-port throttle body was discarded, the newer IAC (idle air controller) was less problematic, and the overall operation of the entire system became much more conducive to the space constraints on motorcycles. In this “dead-head” system, the fuel pump and regulator require only one check valve line. The pressure regulator maintains the pressure on the inlet-side of the injectors. Both the fuel pump and the pressure regulator are mounted inside the fuel tank.

As they have always done in the past, the aftermarket responded brilliantly with a full line of throttle bodies, injectors, tuners, and highperformance air cleaner options. All designed to increase performance, mileage, and in general, the overall ability to customize your fuel injected motorcycle. This also simplified dyno tuning and overall made happier customers and improved quality of ownership.

Just like any other system on your motorcycle, if left to decay, your fuel injection system will fail. Though extremely robust, you can expect to replace the parts in your fuel injection system at some point. I suggest you do this as a preventative rather than as a repair. With a small amount of planning and a few basic tools, along with some basic mechanical knowledge, you can replace your fuel system components to keep your fuel injection system running in tip-top shape.

Pic 2: The Delphi system has only one check valve for feed only. Pic 3: 2001 saw a mid-year switch from a return style system to a single check valve “dead head” system.

Pic 4: Fuel filter replacement kits are available from aftermarket Distributors.

Pic 5: It is always recommended to replace your top tank fuel plate seal when servicing your in-tank fuel system.

You’ll need a few parts to do this job. The good news is that they are all readily available from your local independent motorcycle shop parts counter. Your system will require a new fuel filter kit, one check valve, hose assembly, an internal line (on some models) to connect the pump and filter, and a few different sized crimp [Oeticker] hose clamps. To properly crimp your clamps, you’ll also need a crimp tool. Pic 6: This crimp tool is helpful on oil lines too! Pic 7: The right tool for the job always makes things easier.

In our next installment we will do a deep dive into repairing your EFI system. Until that time…ride safe!