Possibly an awful idea

[Floordford]

So on a normal car before 08, or so, doesn't have any ignition or fuel canceling programing for cruising. Instead of giving a car a whole new custom ECM, which could cost $100-300, could 1 piston or 2 be shut off manually without too adverse of effects?

As I thought about it here are the negative things I came up with. I know it would make the engine run very choppy. Also that disabled piston in still compressing air which takes energy. If a car needs 20 horsepower to stay in motion at 60mph it will probably need 20hp @ 60mph no matter the pistons that get it there. It would mess with the vacuum and possible throw misfire codes.

But does anyone know of any aftermarket programing to let an older car do what these newer cars are doing?

[War_Wagon]

Well if your idea was just to shut off the injector to that cylinder manually, I can see another issue. The air being drawn in to the non-firing cylinder would then be forced out into the exhaust, the O2 sensors would read 4 cylinders worth of air and only 3 cylinders worth of burnt fuel, and the computer would think the engine is running way too lean and richen up the 3 cylinders that were still firing. At least I think that's what would happen, though I may be totally wrong!

[Floordford]

Good point too. Maybe the newer cars with the cylinder canceling systems compensate for that in the programing. Im not sure how to counteract for that being a shade tree guy. I wonder if welding the O2 very far upstream would help. If the cylinder closest to the firewall was deadend but the O2 was placed in the area of the 3rd piston it might help. But no guarantees. Its still getting hit with only 3 fires instead of 4 but at least its not 3 fires and a shot of cooler air.

[RH77]

This has been tried many times without success. I tried a cylinder deactivation project back in 2007 by cutting the injectors, but it didn't work. The ECU expects more oxygen from the 02 sensors and dumps more fuel in the mix. Plus, the setup created quite a lot of vibration in . The only way this works is to physically close the valves and re-program the fuel delivery.

It's a great idea, but difficult to implement.

[Floordford]

I wonder how the newer vehicles compensate for that vibration.

[Ryland]

I think they compensate by having slightly heavier fly wheels, with a v6 or 8v engine you kill half the cylinders so the firing is still balanced just less often, with the Honda civic hybrid they kill 3 of the 4 cylinders and close the valves of the dead cylinders then use the motor that is part of the fly wheel, to even out the firing so it runs smoothly, the closed valves alow the o2 sensor to work properly.

[Floordford]

Wow. So valve and camshaft modification is required. I know some cars come with butterfly valves in the intake manifold to help with low end torque, i wonder if they could be modified to independently close to achieve a similar operation.

[comptiger5000]

^ Yup. If you don't close the valves, you're saving nothing, even putting the fueling issues aside. You need to make those cylinders stop pumping air to gain anything in the pumping loss department.

[Diesel_Dave]

In theory, there are ways to get around things like the O2 sensor and the pumping loses. For example, you could block off your intake and/or exhaust ports on the deactivated cylinders, and drill holes through the deactivated pistons.

However, the issue that is going to be extremely hard (or even impossible) to get around is the vibration issue. This is going to depend a lot of the specific engine that you have. Engines that use cylinder deactivation have been specifically designed so that they're still mechanically balanced even when cylinders are deactivated. You have to realize that an engine doesn't really run at a "constant" speed--the crankshaft (and everything else) is constantly undergoing acceleration and deceleration. A lot is going to depend on the configuration of your specific engine (number of cylinders, firing order, cylinder V angle, flywheel design, etc.).

That being said, I'm not saying this can't be done--but you better really know what you're doing.

[Big Dave]

GM does it by disabling injectors and the pushrods on four cylinders. It works really well but needed a LOT of engineering - beyond your average Joe.