Injector duty cycle and afr

[sy2185]

if i've got my stock chip/turbo/manifolds/injectors on with no alky and 46lbs fp(a little rich) how come on a dm file i took today wot 0-100mph, my afr was around 11.7 but my injectors never went oner 88%dc. why wouldn't the comp. just pull out some fuel to get the afr closer to 14.7?
Jeremy

 

[93ty475]

Re: Injector duty cycle and afr

I'm assuming you're not using a wbo2 and reading the "AFR target" in datamaster....if so, afr target is not an air fuel ratio reading...it's a set value in the ecm....it's programmed to vary with coolant temperature and rpm....also when you go into PE (wot) the afr target is usually programmed to lower (rich) as your engine rpm increases.....in other words, yours sounds like it's normal.....be very careful pulling out fuel pressure to get to 14.7....that's the wrong way to go about this.....it won't happen

 

[Maxtor]

Re: Injector duty cycle and afr

The stock ECM doesn't adjust to target AFR under WOT. Like Servando said, in Datamaster with the stock setup you are looking at "target" AFR not "actual" AFR. Some aftermarket engine management systems such as FAST can provide O2 correction via input from a wideband O2 sensor in closed loop mode.

If you get a WBO2 and are able to read actual AFR, keep in mind 14.7 is stoichemetric (sp?), but under boost at WOT a turbocharged engine needs richer conditions to avoid detonation and make power. Typical AFR's under boost should be anywhere from 11/1 to low 12/1 ratios. I would strongly suggest that you do not back fuel pressure off to lean it out without knowing what you are doing.

 

[dgoodhue]

Re: Injector duty cycle and afr

If you get a WBO2 and are able to read actual AFR, keep in mind 14.7 is stoichemetric (sp?), but under boost at WOT a turbocharged engine needs richer conditions to avoid detonation and make power. Typical AFR's under boost should be anywhere from 11/1 to low 12/1 ratios. I would strongly suggest that you do not back fuel pressure off to lean it out without knowing what you are doing.

Target is just the ECM's guess, it isn't an accurate number as mentioned about . 14.7 is ideal for emissions. Somewhere is in the 15, low 16's is ideal for fuel mileage. For our truck, an air fuel ratio of high 11's is what most popel aim for. My friend with unboosted SBC often shoot for 12.8.