A Lean Cruise Hack for the E40 PCM

In theory would this work, whether its safe or should be done or not is another matter for another day.

I've been reading a couple of threads with interest

https://forum.efilive.com/showthread...ighlight=b3671

http://ls1tech.com/forums/pcm-diagno...rk-timing.html


There is no provision for lean cruise in the E40 PCM,

To get lean fuelling to perform you need to be able to advance timing in B5112 Fuel Mixture Spark correction for EQ values less than 1, this is not possible. And we don't have B3639 lean cruise target EQ to subtract from EQ = 1. Hmmm, so

If we scaled the VE table and MAF to the target lean cruise AFR, 16.9 for example, 14.7/16.9 = 0.87

Using dual LC-1 WB programmable simulated NB O2 out puts and trick the PCM that 16.9 AFR is stoich and is equal to EQ =1 during closed loop operation allowing STFT/LTFT. Set B3671 Stoichiometric Air Fuel Ratio to 16.9 so it is equal to EQ =1

Now to B5112 Fuel Mixture Spark Correction, we can command additional spark advance at EQ =1.0 instead of 0.8 - reference B5908 Fuel Mixture Spark Correction from an LS1 for typical values.

Theoretically we now have lean fuelling for all conditions idle and normal operation, however we can enable PE at very low loads/rpm and compensate for the difference in real and hacked stoich AFR. Around EQ = 1.32 for a real AFR of 12.8. Conditions would be either lean fuelling closed loop idle & cruise or PE, never emissions friendly.


EQ = AFR
1 = 16.9
1.05 = 16.1
1.1 = 15.3
1.15 = 14.7
1.2 = 14.1
1.25 = 13.5
1.3 = 12.5
1.35 = 12.1
1.4 = 11.6


BP Premium non leaded fuel in has a stoich AFR of around 14.35~14.4, regular is 14.7 .

I'm in Australia and I have a Gen3 Holden with lean cruise enabled. It's only meant for high speed cruising... the factory setting for when it becomes active is 76kph (about 47mph). The fuel economy gain you get from lean cruise is very modest. It's probably not worth all that effort to try to hack an imitation lean cruise.