I was wondering is the injector duty is acurate or a "best guess". It does not monitor fuel pressure or what type pf pump you are using, so how does it know how close you really are to maxing out fuel? I think I was hitting low 90's and was thinking of adding a second Denso pump in the tank, but would that really change my #'s?

 

I've always figured it was a "best guess" based on the size of your injectors and throttle.

 

Since the PFC controls the injector duty (which is how it controls the fuel going into the engine), the numbers it is giving you are exact.

Injector duty is just how much the injector is operating, so it doesn't matter what fuel pump or pressure you are running. Changing the fuel pressure will effect the amount of fuel injected for each operating cycle but that doesn't change the injector duty. Likewise, changing the fuel pump only effects the amount of fuel delivery if your previous pump was inadequate.

 

So by adding a 2nd pump, I would only be raising the fuel pressure (if the other one was maxing out) in the high boost high rpm range, and in effect would have to lean out fuel to keep the same AFR's, thus creating lower duty cycles?

 

Adding a 2nd pump will not raise your fuel pressure. It will make sure the pump can deliver enough fuel at the higher pressures (all fuel pumps drop off in output as fuel pressure increases). It will not reduce your duty cycles by itself. You will have to reduce the fuel being injected to do that.

In any case, if your current setup is already delivering enough fuel, then you will notice no difference by going to a bigger pump or 2nd pump setup.

BTW, how the hell are you hitting over 90% injector duty with 1600cc injectors and the stock twins? A lot of guys are running single turbos with 1300cc injectors with lower duty cycles than that. What are your A/F ratios at high rpms under full boost now?

 

I went single this week and haven't changed my sig.

But if a pump is maxing out wouldn't the pressure drop as well as the flow, like in an electrical circuit? It that is the case and I add a pump, I will run slightly richer up top?

I guess I am trying to find a way to decrease my injector duty.

 

Increasing the fuel pressure will increase the amount of fuel delivered, provided the pump(s) can handle it. I don't know anything about the serious fuel pumps so I can't help you there. Increasing the fuel delivered per injector cycle will allow you to retune your fuel maps, lowering the injector duty.

I would ask Max Cooper about this, because I think he raised his fuel pressure above stock with his single turbo.

 

What was the A/F ratio when you last tuned it and at what boost? Depending on the boost level, you might be running rich and need to back fuel out in the upper cells. If that's the case, the duty cycles will drop. Just need to get the wideband hooked up to see where your at before spending more money not knowing if you really need it or not.

Tim

 

AFR's were in the high 10's. Max injector duty was actually 96% at 16-17 lbs (P18-N18). I was thinking more of 2 parrallel pumps as opposed to series. Just wondering if adding a second pump is nessessary.

 

We had the same problem last time at the dyno. Fuel would drop at higher rpm because the engine would take more fuel. The problem was fixed by adding a Vortec T-Rex pump inline to the in-tank pump.