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How Does It Work

dmswildman

By dmswildman
in Ask A GM Technician

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longhorn_giant Enthusiast

longhorn_giant

Posted
Posted

When the truck senses an evening off in load applied to the engine (I believe it has something to do with a vac sensor), 4 of the cylinders are deactivated, and no fuel is injected into them. They are on a seperate set of lifters, so the valves aren't opened during this time. In order to compensate for the loss in HP, the engine increases RPM slightly to maintain the speed. Once the truck senses a load increase, the lifters are re-engaged, fuel is put back into the cylinders, and the RPMs will go back to standard V8 speeds.

Paul58 Enthusiast

Paul58

Posted
Posted

How much of an rpm increase are you talking about? I've never noticed any change in rpm, so it must be very slight.

dmswildman Enthusiast

dmswildman

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Posted

ok, do the cylinders that deactivate change, like one time the front 4 deactivate. then the next time the rear 4 deactivate. that way 4 if the cylinders get more wear.

brims Senior Enthusiast

brims

Posted
Posted

Same 4 every time, I think it's 2, 3, 5, 8.

 

With a tune, I now see a change in RPM when it changes, 25-50 I'd say. It's getting deactivated soon because I can feel it like it keeps 3-4, 4-3 shifting, really freaking annoying. Justin says it's good and bad, means I'm making plenty of power with the throttle plates partially open. It's really annoying, he told me some trucks do that stock.

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