DIY displacement on demand system project

[suspendedhatch]

Limp mode unfortunately defaults to very rich mixture and very conservative timing. You are confusing limp mode with open loop. Open loop is when the ECU ignores the O2 sensor and runs straight off the fuel and ignition tables. This happens any time you mash the gas to the floor and wait for the RPMs to climb past a certain point. It also happens any time you are below operating temperature or before your O2 sensor has had enough time to warm up.

Whether you're burning fuel or not, the cylinders will receive the same lubrication. All your injectors stay closed every time you let off the pedal in gear above 1000 RPM. They turn back on when you drop close to your idle RPM. So lubrication on deactivated cylinders is not a problem. Oil circulation is mechanical. You could turn the crank by hand and it would pump oil.

When a cylinder compresses air without burning fuel it decelerates. I'm not sure but it seemed like you were assuming that since there's just air flowing in and out of the combustion chamber there's no resistance besides drivetrain losses and the friction of the wheels.

You can't deactivate an O2 sensor with a simple switch. The ECU will sense something wrong and throw a CEL. Instead what you want to do is emulate an O2 sensor with normal readings. This is not easy but there may be products on the market that do this. The signal from a narrow band O2 sensor is constantly bouncing from one voltage to another, approximately .4 volts to .9 volts. That is what your ECU wants to see. If it sees nothing at all, or one constant voltage, it's going to throw a CEL and go into limp mode.

If you don't want electric spikes across your switch you simply bridge the terminals with a diode facing backwards. You could also switch relays and put diodes on the relay terminals facing backwards.