Quote:
Originally Posted by Dan Stokes
I'm not sure of M-B's fuel delivery strategy but I wouldn't expect rack (IP) position to be much related to fuel delivery. Generally speaking on a mechanical Diesel injection system fuel delivery is determined by rack position and load. So even if you held the accelerator pedal dead steady the IP would add fuel if you hit a hill and pull fuel out on a downhill (or any other change in load).
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That doesn't sound right...but I admit I don't know. My limited understanding is that the throttle changes the position of the rack which essentially lengthens the stroke of the injector pistons resulting in more fuel being delivered. If that's true, at any given throttle position, the IP would be delivering the same amount of fuel per revolution regardless of load. And that kind of fits with experience - hold throttle constant, speed decreases uphill and decreases downhill.
Thinking it through a little further, it would seem that unless we're talking about a manual transmission car, the slippage in the transmission at various loads, would skew any attempt to calculate mpg based on just throttle position and distance. About the best you could do is use a TPS gauge as a diesel equivalent of an "economy gauge".
01-22-2014, 07:29 PM
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