Magneti-Morelli vs Delphi EFI

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By P.R. (Preacher) Pollard

The new Delphi system is a Speed Density system. It has the ability to compensate for a variety of changes in air mass by using the input from 5 sensors (TPS, MAP, CKP, IAT & ET)
to calculate the "density" of the air that the engine is using at any given time.

The old Magneti-Morelli (a.k.a. Weber-Morelli) system basically has two base fuel delivery maps. A "cold engine map" and a "warm engine map" (programs). It has 3 sensors that give you X amount of fuel for any particular combination of the 3 sensor inputs (TPS [throttle position], CKP [rpm], MAP [engine load]). It used the ET sensor to tell the ECM when to switch from the Cold engine program to the Warm engine program.

The Delphi Speed Density system is pretty much the same as a Mass Air Flow System but it uses more basic (and less complicated) sensors to calculate the air mass needed by the engine instead of using a delicate and complicated (compared to the basic/simple sensors a Speed Density system uses) Mass Air Flow Sensor. It can compensate for changes in air flow enough so that you can add free flowing pipes/mufflers, or a high flow air cleaner without having to re-flash (reprogram) the PROM in the ECM. I know that one person on this list has added both pipes and air cleaner without any problem at all. It has the ability to compensate, but only up to a point. No one has calculated that "point" with any certainty yet. It has a "Range Of Authority" (ROA) and once you have gone outside of that ROA you need to either re-flash the PROM or add a PC-III (Some say both).

You could *never* do that with the old Magneti-Morelli EFI system that Harley has used since 1996. If you added a SE Air Cleaner you required a $150 re-flash. Then when you added pipes... another buck and a half. Cams? One more time... it could get expensive!
Until the Dynojet Power Commander became available. Up to that point you were pretty much at the mercy of the Motor Company... at 150 bucks a pop!


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