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----- Original Message ----- From: "Jim Adney" <email@example.com> > Sorry, I don't think that was a particularly good explanation. I do much better > with sketches and graphs. I know what you are saying.I can visualize it well enough,I think. How about this: " Special Cases: I only have one specific case, the introduction of the 2.0L motor for the 914 in 1973. It's clear that this motor had a different speed correction curve than the 1.7L, but the motor was introduced using the 1.7L's ECU. My conjecture is that Bosch and/or VW-Porsche had not completed the development and design of the 2.0L ECU, so they had to go with the 1.7L's. Higher flow rate injectors were used to account for the basic mixture difference, but that still didn't handle the changes in the Ve curve. To accommodate, Bosch made a slight change in the MPS - they tweaked it to have a richer full-load response, and they changed the resistance characteristics of the head temperature sensor. First, they changed the set-point of the sensor at 20 C from 2.5 K ohms to 1.3 K ohms, and added a ballast (static) resistor of 270 ohms in series. This brought the cold engine (sitting overnight, ambient temp 20 C) resistance to 1.57 K ohms, considerably leaner than before - this was usually dealt with by running the idle mixture richer, but '73's were always a bit harder to get going when cold. When hot, however, the ballast resistance kept the hot resistance value considerably higher (richer) than would the standard sensor. The richer mixture produced good part-load and full-load response, even with the more choked-off Ve response of the 1.7L ECU. Note that Automobile Atlanta has sold a "hot European setup" for many years - a '73 MPS, temp sensor, and ballast resistor. Gives you a richer part-load mixture for more power - oh, and more emissions and higher fuel consumption, too."