Hi Everyone,

I'm new to this forum, and I'd like to thank all of your for the great information that I've learned from here. I can't thank you all enough. When I was a teenager - a long time ago - I worked on fishing boats and picked up what I could about Diesel engines. I used to own a 7.3 PSD on a '94 F-250, and it was a great motor with very few problems. I wish I still had the truck, but I'm now interested in a Diesel Excursion with the new 6.0 PSD. In newer marine engines, Volvo and other manufacturers have what they call "common rail" fuel injection where the injectors themselves are electronically controlled and actuated by solenoids or piezoelectric devices whereby the fuel is injected in multiple brief pulses during a single combustion cycle. (I read about this from a magazine called Professional Boatbuilder, Dec/Jan 2004, but I heard about this before the article appeared).

Here's my question, is the Ford "Hydraulic rail" fuel injection the same thing as what other people call the "common rail", or is it simply unit injection without the multiple brief pulsed fuel delivery? If this is a stupid question, please forgive me and my newness to this area. I'm not a Diesel mechanic, although I wish I was, but I just want to learn more about this. Thanks.

 

This is a quick and crude response to your question-

Common rail is a system where all injectors are fueled all the time- Early gas VWs pumped gas into the intake continuously. With better technology and cheaper computer power, systems evolved to fire injectors in banks and then individually. Early systems all fed fuel to all injectors all the time- but later the injectors were triggered electronically. Common rail was typically a gasoline injection system.

With diesels you obviously had to have greater accuracy in metering. Diesels, modern ones anyhow, also required much higher injection pressures. Certain Cummins engines (not the cheap B Series engines used by Dodge) used a mechanical injector located in the top of the head where it was actuated by the camshaft. Other manufactures used this system as well because it turned each injector into its own high pressure injection pump. Technically, these systems were a common fuel rail system because the injectors were always fed with a low pressure supply of fuel- But we do not associate common rail with these engines.

Common rail today is the system used by most gas engines, and some diesels. Deere uses it in some applications and now Cummins uses a German system licensed by Bosch. This common-rail system continuously distributes high-pressure fuel to all the injectors. An electric solenoid then fires the injector at the proper time for the proper duration. The benefit of the Bosch system is that with the high injection pressures, Dodge can meet emissions requirements where the old Cummins system could not. But the system may have a down side. All of those fuel lines are external and under very high pressure. I am sure the Germans did their homework- the same system in VW 5.0 liter twin turbo V-10 diesel makes over 300 horsepower. From a 5.0 liter!! But Time will tell how well these systems hold up and what kind of maintenance they require.

I think the powerstroke injection system is superior because there are no external high pressure fuel lines. This engine uses a HEUI (Hydraulically-actuated, Electronic Unit Injector) system patented by Caterpillar and licensed to Navistar International. This system is technically a common rail system because all the injectors have fuel all of the time. But the HEUI system does not function like other common rail systems.

The powerstroke diesel takes medium pressure fuel and circulates it to all injectors through passages in the heads. The engine also circulates high-pressure engine oil to all injectors through passages in the heads. An electronic servo opens a passage on the top of the injector which allows the high pressure oil to push the injector plunger. Engine RPM, load, and other factors are all taken into consideration by the computer when it opens the servo for a set period of time. (It also ¡°pre-injects a little bit of fuel for people with sensitive hearing problems. I.e. makes the engine quieter) I like this system because there are no high pressure fuel lines to fail. It also generates very high injection pressures allowing the powerstroke to start better in cold weather and meet emission regulations.

So the answer to your questions is yes and no. The powerstroke is technically a common rail system- but it does not function like other common rail systems. And in my opinion, it is a superior design.

-Mike

 

Hey Mike,

Thanks for the reply and your time. Very detailed and informative and I'm sure others got as much out of it as I did. Great job.

 

Mike
Ever soooo true.......we do continue to learn from those on this forum.

 

Mike
very informative and nicely written thanks

Bob