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      05-14-2010, 07:48 AM   #17
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Drives: 2009 N54
Join Date: Jul 2009
Location: Sticky's Mom House

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Originally Posted by Former_Boosted_IS View Post
Fuel pressure should be dropping at high rpms? That doesn't sound logical, but I will admit I am not the expert here. I am using the JB3 to log the fuel pressure and I have been simply looking at it in Excel. I wonder if there is a scale that is applied to it?

Maybe I need to learn more about pressures from the HPFP?
I've done extensive work with cpe regarding fuel pressure changes/monitoring/pump development on my previous DI car and some on this car. If my memory severs me right stock fuel pressure hits 2200-2400psi down low and falls down to 1600ish on a bone stock car. Yes the fuel pressure drops as rpms rise. Once I get home Ill jump on my tuning lap top to see if i can post some logs for you, but def ask terry about the scaling he is using because those numbers are not accurate.

There is also two ways to request more fuel which both alter fuel pressure. The standback alters the o2 signal to request more fuel and it also alters the actual fuel pressure. I am not sure how the jb3 does it, but both solution raise pressure as expected, however in a different way.

Another thing to think about, being that this is a DI motor which mean pressure is directly injected into the cylinder, af ratios gathered from widebands are not exactly accurate as you request more fuel. Think of it this way, the time frame that an injector has to fire is extremely small and limited, meaning you can only inject usable fuel during that period. If that window closes the valves being to open/close and you are still injecting fuel because your targets request this, the excess fuel that gets injected simply gets blow out the exhaust and fools your wideband into thinking you are running rich.