Low duty cycle?

[Supercharged408]

I am running 48# injectors and about 38psi fuel pressure at idle. I some times stall when I come to a stop, or after idleing for a while. I noticed my duty cycle is only around 2%. I dont think I am idling too rich or too lean to be honest, but I think that 2% is just too low a DC to be stable, is this correct? BTW, at about 7psi and 5000 RPM, I am around 75% DC, I only checked this on the street, so I didnt get up to 6000 and full boost or anything to find what my max DC would be.

Do I have the wrong size injectors?

Damon

 

[Craig Smith]

Nothing wrong with that. At 1000 RPM you have approximately 120 mS available to inject on a V8. This should mean that your injector pulsewidth is around 2.5 mS or so at idle to come up with 2% duty cycle. (All numbers here are ballpark, or course.) I bet this is the case.

When thinking in terms of duty cycle, it is most important to make sure that the injector is properly sized for WOT situations. It sounds like you are right in the ballpark to me. 75% leaves you room to grow, but is still high enough that the car should run well. You don't want "too much" injector. Then, the duty cycle is too low at WOT, which can hurt performance. If you REALLY have too much injector, it can be difficult to get the car to idle properly.

IMO about 85-90% duty cycle at the end of a run is optimal. Everything else should fall into place from there.

 

[Supercharged408]

Thank you Craig, that makes me feal a bit better.

Any idea why I sometimes stumble or stall at idle then? I am idling in open loop because I had a much more irratic idle when in closed loop.

Damon