ecm and dutycycle

[anteversion]

I have a gm maf setup with MAFT gen 2 wich is the same thing than a safc, and working the exactly same way. I'm also running with a small 16g at 19 psi. i've got all the fuel mods like fuel pump ( 255 lph ) rewire kit, but got the stock 450 injectors. So i've setting the base fuel pressure to 42 psi with the vaccum disconnected to make those stock units to act a little bigger. I'm using datalogger to tune and a plxm-300te wideband. The thing is that im actually running the wot settings at -19% to get around 12.0 a/f on the wideband but i'm still hitting near 100% of dutycycle at around 6000rpm.

So my question is: how can the injectors are hitting the 100% DC before the redline even if my fuel settings are at - 19%.

 

[pneumo]

I have a gm maf setup with MAFT gen 2 wich is the same thing than a safc, and working the exactly same way. I'm also running with a small 16g at 19 psi. i've got all the fuel mods like fuel pump ( 255 lph ) rewire kit, but got the stock 450 injectors. So i've setting the base fuel pressure to 42 psi with the vaccum disconnected to make those stock units to act a little bigger. I'm using datalogger to tune and a plxm-300te wideband. The thing is that im actually running the wot settings at -19% to get around 12.0 a/f on the wideband but i'm still hitting near 100% of dutycycle at around 6000rpm.

So my question is: how can the injectors are hitting the 100% DC before the redline even if my fuel settings are at - 19%.

It's because you're running 19psi of boost. More boost = more fuel.
42psi of fuel pressure isn't much of an increase, it makes your stock injectors flow like 480cc injectors. Try upping the base pressure to 45psi. That'll make the injectors flow like 495cc. If that's not enough, try 48 psi -512cc.

 

[anteversion]

maybe but to me it make no sense. What's the difference it may cause if i'm running 10 psi of boost or 19 psi. The fuel pressure will raise with the boost and will make the injectors act the same as with 10 psi of boost?? i have actually set my base Fuel pressure to 50 psi and its hitting the 100% duty cycle at wot. But i really dont understand how the ecm can tell the injectors to reach their flowing limit even if i'm running at -25% on the afc?? i need some explanation about this situation.

Actually wot pulls are at 12:1 a/f ratio. High fuel trim is at 90% ( wich tells that i can even pull more fuel from the afc to get it a 100% ) and afc setting is at -25%

 

[snowborder714]

Why not just buy bigger injectors? That A/F ratio is getting pretty lean.

 

[anteversion]

yeah i know bigger injectors are a need actually, but this is not an answer to my question. and 12:1 is not really lean, thats just good.

 

[snowborder714]

I can't say I've heard of too many people tuning for 12:1 for WOT. I wasn't saying it was wrong, but I'm used to reading and tuning for 11:1.

 

[anteversion]

yeah ok i see. I was just trying to lean it much too decrease the IDC.. i know 12:! is good but also at the limit too.. the thing is why IDC are at 100% aven if i tell the ecm to send less fuel

 

[pneumo]

The FPR does not add fuel as boost rises. It only keeps the pressure difference between the pressure in the fuel rail and the pressure in the intake manifold equal to the base pressure. So if you're running 50psi base fuel pressure, the pressure of the fuel coming out of the injectors will always be 50psi greater than the pressure in the intake manifold, regardless of how much boost or vacuum you're running.

Short version- you need bigger injectors.