Just thinking about that, if we can change just about every parameter for fueling with say a Smarty or Black Maxx, is it that far fetched to have the engine stop injecting all together in 3 of the cylinders, when conditions are right, ie light load on engine, etc?(ie would it harm the engine in any way to not have fuel in each cylinder, lack of lubricity). My 2000 had the 3 cyl high idle, so is it just a matter of how well it would function at like 1500-2000 rpm?


I am by no means an expert here, what things would hold this back from working?

 

lots of other factors than just shutting off fuel. VVT (variable valve timing) comes to mind too.

 

Oh yeah, didnt think about that, does anyone know the technical changes when the engine goes into 3 cyl high idle? All the valves continue to operate, what else could change?

I guess I am saying that they already have shown they can run on 3 cylinders, at least at idle. Would interested to see how it works out.

 

Really, you won't be ahead unless you can crack the valves open on the compression strokes. To do that, need variable valve timing. The reason for the 3 cylinder warmup is that it takes allot of power to push those empty cylinders on the compression stroke. If you don't believe me, look at your egt gauge when the 3 cylinder idles kicks in, it will rise at least 200 degrees and the reason it rises is that the motor is working against those empty 3 cylinders on the compression strokes.

 

I undersstand the reason for 3 cyl. high idle, used it often in the cold here, and why it loads the engine some. The part I didn't think about though was what you just mentioned, the piston would still be compressing that air and not getting the power stroke from that work done. I knew I was missing some key thing like being able to open that exhaust valve. Oh well....

 

Remember the Cadillac V-4/6/8?
Not sure how they did that but it really did not make a lot of difference. My dad had one. Had all sorts of issues with it. Low power, high fuel consumption etc.

 

Here is how they did that...
"For 1981 Cadillac introduced a new engine that would become notorious for its reliability problems (with the electronics, not the robust mechanical design), the V8-6-4 (L62). The L61 had not provided a significant improvement in the company's CAFE numbers, so Cadillac and Eaton Corporation devised a cylinder deactivation system called Modulated Displacement that would shut off two or four cylinders in low-load conditions such as highway cruising, then reactivate them when more power was needed. When deactivated, solenoids mounted to those cylinders' rocker-arm studs would disengage the fulcrums, allowing the rockers to "float" and leave the valves closed despite the continued action of the pushrods. These engines are easily identified by their rocker covers, which each have elevated sections over 2 cylinders with electrical connectors on top. With the valves closed the cylinders acted as air-springs, which both eliminated the feel of "missing" and kept the cylinders warm for instant combustion upon reactivation. Simultaneously, the engine control module would reduce the amount of fuel metered through the TBI unit. On the dashboard, an "MPG Sentinel" digital display could show the number of cylinders in operation, average or current fuel consumption (in miles per gallon), or estimated range based on the amount of fuel remaining in the tank and the average mileage since the last reset."

 

GM LS engines have the multip-displacement technology with only cam timing changes since they are push rod engines. (I think)

Tobin

 

MDS is a real ploy on fuel economy. My good friend had a Honda Minivan that was supposed to disable to 4 cyl mode on the Highway. The change in mileage was minimal and the highway was the best mileage of any vehicle. The in town still sucked back the fuel.

With diesel you have ultimate control of the fuel as the engine only uses what it needs to maintain load. With the losses described from disabled cylinders, the gain is nil.