cambria

It seems to me that our engine computers could be remapped so as instead of the engine running of four cylinders on one side in the "Limp home mode", it could run on two cylinders on each side in a cruse condition and when additional power was required, bring in the remaining cylinders. Then our cars would be considered "Hybird". Just a thought.

dr bob

"Limp mode" is a default rather rich condition that's there to let you get off the highway when you have a MAF failure. The car runs on all cylinders, with a fixed amount of fuel metered via the injectors. With a weak or no MAF signal, the LH has no way to measure airflow to get the right amount of fuel, so it relies on the oxy sensor only.

On the '89+ cars, there's a safety system that drops four cylinders when it thinks that one of the two ignitions has failed. It works based on temperature differential between two exhaust points, one on each side of the motor. When it thinks there's a cold port due to no ignition, it shuts off fuel flow to the cylinders fed by the one distributor that has cold exhaust. So it does fault two cylinders on each side of the motor. There have been warnings about breaking the driveshaft due to torsional vibrations when driving the car in four-cylinder mode. The valves on the dead cylinders still allow charge air and exhaust flow, so pumping losses would likely eat up any possible savings one might expect from running on only half the cylinders.

Jim bailey - 928 International

As Bob says .....bad idea to run as a rough 4 cylinder and a big 4 cylinder air compressor shooting air into the exhaust. GM tried it years ago with Cadillac 500 cube, the "4-6-8" .

69gaugeman

Current systems selectively shut off cylinders in (somewhat) random order so all cylinders will still see combustion

Vilhuer

Porsche was doing research in this field during second oil crisis for Ford and itself using 928 engine. They were not happy how well system worked and abandoned idea once fuel prices got lower again.