i doubt he is hurting anything. however the deactivated cylinders are creating tremendous pumping losses.
you really need to keep the valves shut on the dead cylinders. i have often thought about removing the lifters on 1 of the cylinders of my engine and also disconnecting the fuel injector. sence its an overhead cam, its quite easy to pop the cam cover and lift out a few lifters....
In a modern engine, your oxygen sensors would pick up that you are way too lean, and then increase fuel to the remaining cylinders. The end result would be three cylinders running way too rich and 3 cylinders deactivated. Then the excess fuel would be burned in the exhaust and converter.
This might work on an older car without an ECU module but I can't see an O2 sensor ignoring that much more oxygen in the exhaust.
Also, you can't get 50 mpg on a big van on the highway even if it had only a 3-cylinder engine. Heck, the tiny little Geo Metro only had 3 cylinders and it didn't get that gas mileage!
Glad to know I'm not the only one with these weird ideas.
I thought about doing this on my old Plymouth Acclaim when I had it. I read about a guy who had his 4 cylinder Acclaim running on 2 cylinders (by accident)...gave me the idea.
I wonder if someone really could design a new computer for certain cars that would give them DOD? And be able to sell it for a reasonable price...that would be the quickest way to saving fuel in the country.
I pondered a similar idea, but got lost in a circuit design as I would be dealing with a 5-cylinder engine - it would have to allow cylinder activation every other injection pulse (electronic background is touch-and-go hobby level).
Then like other's have said, you have some pumping losses to deal with, and as long as rpm's are high enough (say at least twice idle rpm), than I would think torque pulses from combustion would be similar to what's normally appearent. Additional negative torque pulses would be introduced from dead cylinder compression of an air-only charge I'd imagine...this all leaving the harmonic effects upon the crank and main bearing clearences in question.
I also had concerns about how the OBD2 would react, knowing it likely to trigger injector codes unless given a dummy load rather than an open circuit. Then there would be differing load information it would pick-up relative to throttle position between cut-off activation, as sensed by the mass air sensor, the TP sensor again, and oxygen sensors (perhaps even the coolant temp.).
As this is my one and only ride, I've opted to leave well enough alone. I also do most city driving so I don't think I'd find much of any gain with the system...but conservation is conservation!
In thought, not running cylinder deactivation alternately when engine loading conditions allow (meaning not to have the same cylinders deactivated eash time), on an engine with an even number of cylinders, would creat uneven wear characteristics, as well as build-up potential - oil beyond rings and intake valve seals. That's without considering valve deactivation. With considering valve deactivation I suppose oil contaimination wouldn't be near as much if any concern. I think uneven wear might still be a concern - increased thermal and force loads upon those cylinders that continue firing.
Just my thoughts.
I don't know about all this but I've found that brake pedal deactivation helps my gas mileage. And about pumping losses, I'm going to try something. My Civic has a manual transmission and the next time I'm on a long downhill I'm going to try coasting with the engine off and in gear, first with the throttle wide open and then closed to see the difference in pumping losses. I don't know what it will mean, but I'm going to do it anyhow.
Additionally, I am thinking now that having all that oxygen pumped through the exhaust may create combustions in the exhaust system and melt the cat. I can think of a few ways to aviod that problem...but none that are real easy to implement.
This may be one of the few reasons why you can't just cut the fuel off...and need the valves closed
For a standard pushrod engine...I can think of a way to rig this on a car not originally built with DOD. No telling if it would work...
Interesting point BatmanLS1 - I forgot further error introduced by the pumped air from the dead cylinders through the exhaust system, monitored by the O2 sensors. I believe someone mentioned about creating a condition where the air-fuel mixture would thus be excessively enriched...perhaps due to this type of set-up/occurrence.
Burning of the cat. might be another possibility, esspecially if the firing cylinders are forced to run rich.
as long as you deactivated the dead cylinders by stopping the intake and exhaust valves from opening, you would not effect the mixture to the remaining cylinders.
for example. say someone disconnected injectors 1 and 3 (of a 4 cylinder engine). then you would need to remove the lifters off cylinders 1 and 3, so the valves on 1 and 3 would not ever open. problem is that you need some sort of mechanical device to do this.
then, the exhaust wouldnt get extra air pumped in, the o2 sensors would not notice anything off and also there would not be wasted air being sucked through the maf.
are you guys interested in seeing someone a little more subjective try this? i could pull the lifters out of a couple cylinders of my engine in probably 30 minutes. my injectors use clip on wires so its very easy to disconnect them.
it would not be displacment on demand, but rather cutting the displacment in half to get more mpg.
Don't the factory DOD systems alternate what cylinders are firing? I wonder what kind of problems can come from having the same cylinders not firing all of the time.
Also, I seem to remember in an interview somewhere that a GM engineer said they could have just cut off the fuel, but it didn't give much gain because the disabled cylinder was pumping air. By keeping the valves closed, they get that energy back from pressure on the downstroke.
I think the guy is full of crap. The distributor and/or computer is still trying to fire the cylinders when each reaches TDC. There is no way that the engine would run smooth. It would have a nasty skip or sound like an odd-fire buick 225 used in the early CJ5's.
The DOD systems (we'll use the HEMI for example), actually turn the engine into a 4 cylinder and change the timing and firing order.
Well I'd figure that due to the relative load shift to the cylinders that are kept active, timing would be automatically adjusted via computer monitoring. As far as it be correct is up to the programming and sensitivity of the sensors/ECM.
As for the commment of irregular firing and rough running - because the cylinders that are to be deactivated are taken out of the firing sequence at even intervals, things won't sound or feel uneven. As long as the cylinder deactivation occurs at speed, the engine won't try to buck itself from it's stable - this is my concern for Master ACid (for which I recommend he run the engine around twice it's idle speed or more if he goes ahead in testing. Also wonder how the lack of the engine being at temp. is going to throw realtime metering/effective operation?).
Member # 6237
posted February 01, 2006 08:44 PM
"Well I'd figure that due to the relative load shift to the cylinders that are kept active, timing would be automatically adjusted via computer monitoring. As far as it be correct is up to the programming and sensitivity of the sensors/ECM.
As for the commment of irregular firing and rough running - because the cylinders that are to be deactivated are taken out of the firing sequence at even intervals, things won't sound or feel uneven. As long as the cylinder deactivation occurs at speed, the engine won't try to buck itself from it's stable - this is my concern for Master ACid (for which I recommend he run the engine around twice it's idle speed or more if he goes ahead in testing. Also wonder how the lack of the engine being at temp. is going to throw realtime metering/effective operation?)."
The timing and ignition would not "adjust" if you stoped the injectors from opening. Number one, that engine uses a distributor, so the amount of time between each cylinder firing is fixed (+/- the advance). Not to mention that the firing order is 1-2-3-4-5-6. How could you disconnect those "at even intervals"? It WOULD RUN LIKE CRAP. Period. The only engines that would run well with cylinder deactivation would be one that was designed that way.
If you want cylinder deactivation: buy a HEMI.