Hi everybody. I recently installed a GEN VII with wideband O2 and have a question regarding the target A/F ratio. At 14.7 it runs VERY rich, you can smell raw fuel coming out the exhaust. Before putting in the GEN VII, I gathered data from my scanner on the stock ECM. As an example, at a steady 60 mph cruise, level ground, 4th gear, very steady MAP and throttle position, the injector pulse was 2.4 to 2.5 ms. My plan was to then adjust the A/F ratio to get this same inj. pulse and then I would know what A/F ratio the engine was running before the GEN VII swap. I did this for all conditions, idle neutral, idle drive, light accel, decel, etc., and also recorded the timing under all the different conditions. Problem is, the leanest I can get the above mentioned cruise is about 16.5 to 1 before it starts to surge telling me it's too lean. Whats bugging me though is that I can't get the inj. pulse below about 2.9 to 3.0 ms. Same situation at idle in neutral, before DFI scanner showed 1.9 to 2.0 ms. Now, at 16.5 to 1, DFI shows 2.4 to 2.6 ms. I'm not using sequential, so each injector is firing twice each time the cylinder fires, same as before. Why are my inj. pulses longer than before? Any ideas?

 

Are you using closed loop fueling with a wideband O2 sensor? It sounds like an exhaust leak could be causing the O2 sensor to think it's leaner than it really is and thus giving you the extra fuel. Try things in open loop to see if you can get the pulse widths more in line with what they should be.

Also, check the pulse width predictor screen to get an idea of the expected pulse widths that your programmed VE and A:F tables will generate. Compare that to what you are seeing with and without closed loop correction turned on. The predicted PW values should be pretty close to your observed values when you are running in open loop.

 

I have not tried open loop, I will try that. However, when running different A/F ratios from 14.7 all the way to 17.2, I get the same injector pulse, but the car definitely runs different. How can I be getting different A/F ratios at the same injector pulse? Shouldn't running leaner use less fuel? It just doesn't make sense to me.

 

That sounds way wrong. The pulse width number shown in the software is the maximum individual pulse width for all cylinders. Check your individual cylinder fueling coefficients to see if one cylinder is getting an absurd amount of fuel jammed into it. Also check your transient fueling tables for incorrect values -- make sure that both the dTPS and dMAP tables are zeroed out for the lower rates of change.

 

I will look at those also and let you know what happens, although it will probably be a few days before I get a chance to drive the car again.