Interesting problem I have. My fuel pump (or other fuel component) is causing a fuel pressure of about 25psi. The result is that it will run lean if the vehicle is in open loop. When in closed loop (commanded EQR=1.0) the fuel trims are able to compensate.
I am running COS 5 and have set the commanded EQR vs. RPM (B3647) to 1.0 for all MAP/RPM cells. When the PCM is commanding EQR=1.0 it uses the STFT's to trim and it will run perfectly fine.
However, I'm worried about startup where its normally commanding a rich mixture. With the low fuel pressure it will be very lean during startup even when commanding rich. What do I need to change to force closed loop (EQR=1.0) during startup and warmup?
I need to do this temporarily so I can limp the truck to my shop to change the pump.
Thanks.