Engine/Transmission (1994 - 1998) Injection Timing with Plunger Design

[Boldt's Wagon]

Injection Timing with Plunger Design



I ran across a book “Diesel Mechanics†by Erich J Schulz, 1977, McGraw-Hill. The quotes below are not intended to provide fuel or reignite the pump/plunger design discussions in the previous months. The quotes are generic to the Bosch injection pumps and not specific to the Cummins 5. 9 pump.



Section 4, Unit 29 discusses American Bosch Fuel –Injection Systems. In this section he describes three plunger designs, lower-helix, upper-helix, and double-helix. To selectively quote from the book:



“The upper part of the plungers have a vertical and a horizontal machined-out groove and, depending on the purpose for which it was designed, has one or two spiral machined-out grooves. The spiral machined-out groove is called the helix. The shape and the position of the helix govern the fuel delivery curve and either the beginning or the ending of injection.



…. The lower-helix design beginning of delivery is constant and their ending of delivery is variable. (I believe this is the helix design on the Cummins 5. 9 thus fixed timing)



…. The upper-helix design have a variable beginning and a constant ending of delivery. …. When using a plunger with an upper helix, the inlet port does not close at the same plunger height; thus, we say that the beginning of delivery is variable. Closure of the inlet port depends on the position of the plunger helix as it is placed by the governor. When the governor is in the full-fuel position the beginning of delivery is earlier (advanced). When the governor is in the idle-fuel position, delivery begins later (retarded). Regardless of the plunger position, the ending of delivery always occurs when the edge of the horizontal groove on the plunger opens the spill port.



…. The double-helix plungers have upper and lower helices. Both the beginning and the ending of delivery are variable with these plungers. When using a variable-beginning and variable-ending plunger design, the beginning of delivery occurs as if using an upper-helix-design plunger, and the ending of delivery occurs as if using a variable-ending plunger. â€



Thus, timing of fuel injection with the P pump can be controlled. Only Bosch and Cummins know why they selected a fixed timing for the Dodge Cummins 5. 9. Maybe there are P pumps out there that have double-helix plungers.



Another quote: “Some plungers have a small starting groove cut above the helix. This assists the engine in starting by supplying more fuel and retarding delivery. â€



Another interesting comment in a section on diesel fuel: “The difference of power output between Number 1 Diesel and Number 2 Diesel is between 4 and 11 percent depending on combustion chamber and fuel-injection pump design. †I guess winter fuel is poorer performing.

 

[T. Baker]

What the heck is this thing? {“}

 

[R.ebel]

Boldt's Wagon,

Sounds like some interesting reading, I need to add that book to my library



T. Baker,

I think this {â??} is some kind of quotation mark. Wow it won't even cut and paste correctly?

 

[bighammer]

I have Diesel Engine & Fuel System Repair by John Dagel. They explain that a little bit as well. The illustrations are very helpful as well.



I have been curious about modifying the plungers on our pumps for varying timing, but just don't have the time, tools or smarts.

 

[Missouri Mule]

I think you need to "copy" then "paste". “ / …

 

[LHallmark]

Boldt's Wagon is correct about the difference in No 1 and No 2 fuel. Here in Alaska the stations change over to No 1 on their first refill in Oct. The BTU content of 1 is lower than for 2. My mileage drops 3-4 MPG during the winter and jumps right back up in the spring. Driving around in the lower 48 I have found that a fill-up of No2 in a warm climate, driven into a cold climate retains its mileage figures, so it's not the temps that cause the change... ... I had initially thought winter temps would give better mileage since the colder air is more dense. The fuel makes the difference.