Re: bigger engine with e12 injection/ECU perf. mods.

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: I may be mistaken, but I was under the impression that these early L-Jet systems did not have much in the way of a mapped out fuel curve. I thought they relied pretty heavily on input from the airflow meter, and then the balancing effect of the O2 sensor. I could be wrong, but I thought that the mapping of the fuel curve, along with ignition as well was introduced with the first Motronic systems. Obviously there must be some rudimentary program in the L-Jet ECU, but there is no changeable chip as in the later boxes. I guess that's why the turbo tuners have hd such good luck with the rising rate regulators on these early systems. Since the ECU & O2 sensor are always shooting for 14.7 to 1, and since the ECU & airflow meter remain stock, the only way to get the O2 sensor to see 14.7 on a modified/larger engine is to bump up the pressure. In the newer systems, quite a bit can be accomplished with a chip, up to the limits of the stock injectors. At that point bigger injectors can be used at stock pressure with yet another custom chip for really modified situations. I think the 530's were tuned rich at the factory because of the thermal reactors. That, coupled with swapping to a 2.8 gave the little motor plenty of fuel to work with. You were probably running 12 to 1 all the time (no O2 sensor). That would be best for power but like you said would really suck up the gas. Frank? : -Cliff : : Frank- : : What is you opinion about using the U.S 528i ECU w/O2 sensor on a 3.5L(either Euro or U.S.-I don't think : : it should matter)? If the injectors have enough duty cycle available, I would think the O2 sensor would : : keep the mixture right. The O2 sensor is not involved at WOT anyway. I guess if it leaned out at high : : rev./WOT, a rising rate fuel pressure regulator could fix it. What do you think? : : -Cliff : : Cliff, : : Using a US 528i ECUw/O2 sensor on a 3.5 l engine would probable work OK. The issue here is not duty : : cycle of the injectors but the actual fuel advance curve regulated by the ECU/air box, the O2 sensor alone : : I don't think would have enough capacity to change the fuel mixture radically, it's just supposed to "fine tune' : : the system. I have done some playing using the stock fuel regulator in my daily driver Euro 528i(and a US 528i) to both : : increase horsepower and the opposite(to increase mileage)changing the ECU to a 80 635i/M535i increases the amount of : : fuel injected throughout the rpm range slightly but changing the ECU/airbox changes it noticeably. Also switching : : back to the stock ECU/airbox leans the mixture out. Years ago I had a US 528i and the most potent combination for : : power was (believe it or not) a 77 530i ECU/airbox, switching just these two items the car seemed to gain lots of bhp, : : but also mileage sucked. Strangly enough putting the 80 528i ECU in the 530 and the 530 wouldn't start! Has anyone out : : there ever methodically tested the results on emmisions/bhp between switching ECU/airboxes on a stock car? : : Regards, : : Frank

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