injector line size affecting milage?

[DLang]

in reading theough the Haynes diesel engine maintinance I notices that it said that the ID of the injector lines changed from year to year, getting larger over time.

I've read the article about the differences between the different pre-cups between the years and I was wondering if the lines could have any effect on things (the larger line has more volume between the injector pump and the injector, with any air or bubbles in the fuel it would compress slightly more with a higher volume, affecting the amount and timeing of the fuel a small amount)

thoughts?

David Lang

[Bnave95]

Smaller line size for the DB2 pump. DS4 used the larger ones.
Air in fuel lines is a no go. If there was air in the injection lines the injectors would not work well if at all. A lot of running issue can be traced down to air in fuel lines. The best check for this is a clear tubing off the return line at front of pump.Bubbles will cause running issues.
This is good info,http://www.thedieselpageforums.com/tdpforum/showthread.php?p=185457#post185457

[DLang]

from the hayes manual. page 2.-32

quote:

for example, most lines are 26 inches in length, but their inside diameters vary, according to the year of production. 1978 and 1980 lines have and I.D. of approximatly .073 inch. 1981 lines have an I.D. of 0.75 inch. 1982 through 1984 lines have and I.D. of 0.78 inch. And so on.

[DmaxMaverick]

from the hayes manual. page 2.-32

quote:

for example, most lines are 26 inches in length, but their inside diameters vary, according to the year of production. 1978 and 1980 lines have and I.D. of approximatly .073 inch. 1981 lines have an I.D. of 0.75 inch. 1982 through 1984 lines have and I.D. of 0.78 inch. And so on.

The differences they reference are not significant for performance, at all. It is critical, though, all the lines must be of the correct material, ID, length, (overall internal volume) and age. The material can become work hardened over time, so age is a factor. The reason(s) for GM changing the line sizes could have been as simple as sourcing in some cases. Ideally, the lines should be as small as possible, and able to maintain required flow characteristics.

That being said, I have mixed/matched (out of necessity) injector lines of various years and design, and even fabbed a couple lines for temporary use. I could tell no difference by ear, mileage, or my butt dyno. I'm sure there was a difference, but I couldn't tell.

[Warren96]

Butt dyno? That must be a new service tool. Do you have a part number for that? Does it take up a lot of room in the shop?

[DmaxMaverick]

Butt dyno? That must be a new service tool. Do you have a part number for that? Does it take up a lot of room in the shop?

Mine doesn't take up much room and I take it just about everywhere I go. It's very portable, but not custom or modified (OEM). Some others can be quite large and not so portable. If you don't have one, you can't get one. Well, not one that works properly, anyway. If you have one, careful not to lose it. That can be costly. I lost mine before, and it wasn't cheap.

[Robyn]

Butt Dyno, interesting way to refer to ones seat of the pants feel for horse pressure.

Just my two cents. In reference to the original post and ?????????/
If you notice the lines have all sorts of twists and turns in them, this is to allow all the lines to be exactly the same length and therfore keeps cylinder to cylinder timing the same. The length controls the time it takes for the pressure pulse to reach the injector.

A side note, if the lines were of unequal length the "Butt Dyno" would give some very unpleasant readings.
Robyn

[vaceros]

i seem to remember fom physics that a larger diameter of tubing will exert more pressure through the tip of the injector; as well as volume with repect to time. it is like leverage in mechanical, combustion, and flow terms.

[DmaxMaverick]

i seem to remember fom physics that a larger diameter of tubing will exert more pressure through the tip of the injector; as well as volume with repect to time. it is like leverage in mechanical, combustion, and flow terms.
Not exactly. The pressure at the injector will be exactly the same, regardless of the tubing size. The tubing size and material can effect the shock wave of the fluid pulse (fuel in this case). The pop injector fueling event is determined by the pressure pulse, and different tubing size/material can harden/soften that pulse, causing the pop to be early/late. Under normal hydraulic circumstances, this wouldn't make much, if any, difference. The fuel timing/volume on these engines is critical for many reasons, and that makes the tubing issue critical, as well. When smooth and efficient running depends on all 8 cylinders being in sync, one or more lines of different configuration can effect the balance, however slight. Also, a larger tubing volume will exaggerate an air problem.

The pressure difference you refer to can be effected by the size/stroke of pump piston, or pop piston. Both of these being the same, the tubing size won't effect volume or pressure.

[vaceros]

i guess thats true bigger is not always better.