Tuning my WOT and I'm coming to the conclusion that my mid 4000 range wants less fuel than before it, and, after it.

Makes no sense to me but if I make it even just even with the area beneath the engine runs sour mid 4000s and I get pretty rich readings from the wideband. I shift at 6k so I still have alot more to go and the fuel peaks out at 5600 rpm in the ve curve.


Anyone else encounter this up then down, then up again VE curve on their engine?

 

It could very well be fuel pressure harmonics from the batch fire. It could also be manifold harmonics. It could also be something you're missing in the calibration.
My guess: Fuel pressure harmonics - when all eight injectors fire at once, and then all stop at once, a pressure wave travels through the fuel rail, and there has to be a natural frequency to system. If you were to add a small non-rigid reservoir to the fuel line, near the rail, the system may change and reduce the problem. It's probably not worth it though.
One thing to check is whether the injected pulse width is actually going down in that area. If it is, then it indicates some harmonic, if it doesn't it indicates a problem in the calibration. Either way, just tune around it and ignore it in my opinion.

 

You are tuning a WOT with your WB, one thing you didn't say is did you set your P.E.%change to Fuel/air Ratio Vs. RPM at the same number (asking for same AFR) at every rpm in the table.

Because the setting from the factory in some .bin ask for different AFR at different RPM.

PAT

 

i have disabled PE (im running open loop) and have a commanded afr of 13.0


Interesting theory redngold. I had previously thought I was missing something, maybe had the area beneath it too rich and it wasnt showing up because it was still under pump shot or something, so Ive purposely done WOT pulls from well below that rpm but its still happening.

I had tuned around it, just my last couple bins i tried making things even just to satisfy me.

 

RednGold, Pablo is running tbi not mpfi or tpi. I don't think he would run into the same problem as you've mentioned.

Steve

 

Good point (TBI). But, it's still possible - but it's probably less likely. I'd like to see what the injected PW is doing. If it doesn't show the same trends, then something is going on. Otherwise there is some aspect of the calibration that is causing the change, and it's being compensated for in the wrong place. I'd guess it's not an actual dip in VE, though.

 

VE can dip, because VE is a result of engine breathing combined with the effects of intake & exhaust acoustics. If the intake and exhaust plumbing were infinitely long, the VE would be controlled only by the flow restrictions of the valve & head, the cam timing, and the flow resistance of the throttle --- so there would be no significant acoustic effects. With finite-length intake and exhaust paths, you do get acoustic effects on VE, as superimposed on the basic flow parts of VE. The acoustic part is what causes the peaks and dips. In the familiar TPI engines, VE gets a big fat boost near 3000 rpm, due to the acoustic effects of the long runners.

Also note that the VE is a function of both the engine rpm AND the throttle angle, because the throttle blade(s) act as an acoustic valve that can be nearly closed, partly open, or fully open.

So you can have acoustic pressure oscillations in a plot of VE, when plotting in 3D with VE in the vertical, and MAP (which is basically one measure of throttle angle) and engine rpm on the other two axes.

Pressure oscillations can also happen in the fuel system, but I don't think the effect is as significant because the FPR (which controls the static fuel pressure and acts as a surge damper). HTH.