Many years ago I remember reading an article in Mechanics Illustrated about the Mercedes Benz diesel engine. It said something to the effect that Mercedes engines had a built in fuel savings feature that kicks in everytime the driver goes coasting down a hill. Do our First Gen Cummins injection pumps have this feature? In other words are our pumps cutting the fuel supply to a lesser amount when coasting than when idling? If not, does this mean that we are using more fuel coming down a long grade in 4th gear than in overdrive?

 

Actually, every internal combustion engine has this feature.

To check this out, simply observe the pyrometer when descending a grade; it will drop to ZERO, meaning no fire in the cylinders.

 

Uh, you might want to check your pyrometer...

Less fuel per stroke is injected on overrun than at idle, the governor is trying to slow the engine down by taking away fuel. I don't think you will see a measurable difference between 4th and 5th on a downhill run where no throttle input is needed to maintain speed.

 

Did a 4 mile 12% grade down, Pyro saw 150 or so, 5 th and 55 mph
Peter.

 

Wow, where was this?

 

if your pyro drops to zero you got a big problem, cause our engines are compression ignition remember, no heat = no bang = no crankshaft spin = really BAD, there is alot of air and not much fuel moving through the engine but still enough to keep it running.