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Old 02-01-2008, 12:17 AM   #11
Scooby Newbie
Member#: 67483
Join Date: Aug 2004
Location: Sacramento, CA
2005 WRX STi


Originally Posted by williaty View Post
This should make it clearer.

OK, that's a graph of 3 different general shapes for fueling error graphs. Unfortunately, in the real world, you'll usually be seeing 2 or more of them going on at the same time

Error Type 1 is a vertical offset or zero error. The graph has a general trend all in one direction and basically all the same amount. This can be caused by things like incorrect injector scaling, placing the MAF in a different-than-stock sized housing or a new bend before the MAF. This can be fixed with either MAF scaling or Injector scaling. You should alter whichever scaling you've physically changed. This means that if you've just changed injectors, change the injector scaling. Likewise, if you've just altered the intake somehow, change the MAF scaling.

Error Type 2 is a slope error. The graph may or may not all be above or below zero, and it won't all the the same amount. What it will be is a straight line with a constant slope. This is likely caused by injector latency, but with how ornery MAFs are, I bet you could cause this to happen by changing the intake too. This can be corrected with either Injector latency or MAF scaling. Again, fix the scaling for whatever hardware you just changed.

Error Type 3 is a random error. The graph isn't a straight line, has peaks and valleys, and is in general just a mess. 9 times out of 10, this is the MAF being pissy about resonance and turbulence in its new home. This can only be fixed by MAF scaling. Adjust MAF scaling until the error is a straight line, then evaluate it for Type 1 or 2 error lurking within the MAF scaling corrections you just made. Again, if everything was alright before, and you just changed the intake, and then you got a bunch of fueling error, MAF scaling is what you want to change, not anything else.

So as you can see, you can fix any error with MAF scaling. It might not be the right way to do it though.
Voted 5.
Best general tuning post of the year.
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