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Old 06-29-2012, 06:15 PM   #24 (permalink)
t vago
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Quote:
Originally Posted by Mustang Matt View Post
Racers have been cooling fuel forever.

It has the benefit of lowering intake air temps which in turn lets you run more timing. In fact, I would expect in the above dyno charts that pre-mod, the ECU was pulling a small amount of timing due to intake air temp.
That may well be true, but...

The engine represented by the above dyno run has its intake air temp sensor well before the fuel injectors. Injected fuel will not affect measured intake air temperature because of this. Furthermore, there is no knock sensor for the above engine configuration.

I still suspect that the above engine was not running in a balanced fashion. In other words, some cylinders were getting more fuel by mass, and some cylinders were getting less fuel by mass. That is because the fuel was getting heated up as it made its way from the fuel line, through the horseshoe-shaped fuel rail assembly, and feeding cylinders 4, 2, 1, 3, 5, and 7 (in that order) with progressively less dense fuel due to heating effects. Cylinders 6 and 8 (again in that order) would see the same thing, only much less severe.

Since that particular engine configuration only had one pre-cat O2 sensor, and since the engine computer can't do a per-cylinder delivery adjustment anyway, the engine computer was going nuts trying to maintain the correct amount of fuel for all cylinders, and it simply defaulted to a richer-than-necessary fuel trim to compensate.
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