fuel enrichment questions: fresh VS tired engines

[JDmills]

I was just thinking about adjusting the ALDA screw on the 300TDT, which has never been fooled with... and it is approaching 268K... So it is rather slow off the line, and not real quick anyway.

My question became, why do diesels often respond to fuel adjustments as they get older, and yet they still seem to get decent fuel ecomomy?

Not that I know what kind of ecomomy this thing would have gotten at fifty thousand, but I assume it wouldn't be too much more than I am getting now.. So does the injection pump deliver less fuel as it ages? in conjunction with a combustion chamber that may not quite optimize it's conversion into work.. and if that is so, why wouldn't it get crappy fuel ecomomey..

Or is fuel economy a funciton of operating at less than full output, which is not AS effected by wear of components.. And does wear on the components have a greater effect on the power output, as well as "ecomomy of" fuel usage at a higher power output..

[Brian Carlton]

Fuel moves the vehicle.

The vehicle gets fuel when you open the rack.

You open the rack when you press down with your right foot.



The remainder of the discussion is related to the following two paramenters:

1) How much fuel is delivered with a given movement of your right foot.

2) How much fuel is delivered with maximum movement of your right foot.


With regard to the former, the factory does not want the diesel to smoke. Therefore, they will err on the "lean" side of the equation. Give the engine less fuel than what can be used with the available air. If you do that.........it cannot smoke.

The major issue with a diesel is that it gets significantly more air when the turbo spools up..........so...........it cannot get full fuel until that happens........or it will smoke. The ALDA is the device that prevents the smoke.

You can tweak the ALDA to provide more fuel under part "throttle" conditions. You won't need to move your foot quite as far to get the vehicle to "move". Or, you can remove the ALDA completely and modulate fuel with your right foot. Just don't give it too much fuel when it's below boost conditions.

The '86 has no ALDA for the past year. The fuel economy is unchanged. It gets a consistent 28 mph in varying conditions including a/c operation and speeds of 70-75 mph. Naturally, I don't use more than 1/2 pedal when the boost is not present.

[JDmills]

Originally Posted by Brian Carlton

The remainder of the discussion is related to the following two paramenters:

1) How much fuel is delivered with a given movement of your right foot.

2) How much fuel is delivered with maximum movement of your right foot.

.

OK I understand more about how the injection pump works. Excellent description and simply stated, Brian.