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Old 11-16-2005, 10:30 AM   #1
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Cylinder Deactivation

Author: Harrell, Rick
Some of today's modern V-8 and V-6 engines utilize a complex mechanism known as "cylinder deactivation" or "displacement on demand". This feature is reserved for the newest models and those vehicles with the need for a large engine (such as an SUV, Pickup Truck, or Minivan). In some cases, as the DaimlerChrysler Charger/Magnum, a large "HEMI" engine uses cylinder deactivation to cut half of the cylinders under steady cruise with light throttle (on a car/wagon with a powerful engine). GM and Honda also have similar technologies. The process is quite complex and requires cutting fuel and air to the cylinder bank using a mechanical process.
This author has brainstormed with this idea before it has become mainstream, but I never really realized how to do it. I then learned on this website that merely cutting power to a series of injectors would essentially achieve similar action. This seemed much easier to implement. The test vehicle is an American-spec 1998 Acura Integra LS 3-door, with the 1.8-Litre DOHC, Non-VTEC, 16-valve, 4-cylinder engine, with an automatic transmission. Although the experiment did not achieve increased fuel economy, further investigation could yield a way to cut fuel to all cylinders during zero throttle input (coasting) and could potentially increase economy. During coasting, this model of vehicle pulses fuel into the cylinders. Complete shutdown could, hypothetically yield an increase.
I would not recommend using this procedure on the 4-cylinder engine configuration, similar to mine (described later). Inline-5, Inline-6, V-6, V-8, and potentially H-4 and H-6 (Subaru, Porsche) engines could yield a balanced firing order and even cylinder placement. Unfortunately, my engine failed to perform due to reasons which will be described later.
Deactivating cylinders in low engine-load situations and/or zero-throttle input will yield higher fuel economy.
At idle, deactivating the 2-cylinders that worked together yielded in a very unbalanced combustion process, and caused the engine to rock violently forwards and backwards. The only way I could get smooth operation was to run the vehicle at engine speeds upwards of 4000 RPMs. The "LS" engine is a transversely-mounted 4-cylinder that fires at 1-3-2-4 – meaning that cylinder #1 combusts, moves downward, then the same for #3 (probably together). Then the cylinder moves back upward into the compression cycle while 2 and 4 fire. Cylinders 2 and 4 are at Top-Dead Center, when 1 and 3 are at their bottom-most position, etc. Basically there would be a firing of the top 2 cylinders (#2 and #4), then a long pause when 1 and 3 came back up and then down, creating very unbalanced sequence of events and a rocking sensation. This wasn't noticed at higher RPMs because the cylinders were coming back around quick-enough to not create a significant vibration. By the way, cutting fuel only and not fuel and air, results in the deactivated cylinders becoming air pumps. This may have confused the oxygen sensor and catalytic converter. A computerized fuel management system would be recommended to work in-tandem with the deactivation
Operating at 4000+ RPMs and utilizing 2 cylinders resulted in the 2 cylinders becoming overly rich, and used more fuel that if all 4 were working as usual. For those out there who have an engine that would accommodate this idea, feel free to experiment, but first
You are assuming your own risk by performing modifications to a vehicle that is either stock from the factory, or has been modified within the scope of local laws; furthermore, this author and/or this website cannot be held responsible for damage resulting from experimentation.
  • Do I really want to do this? and if I mess this up badly, do I have another vehicle to get me to where I want to go while this one gets fixed. Be cautious, this is not your everyday experiment.
  • Get to know your engine. Using the Internet or repair manuals (available at your local library's reference section), find out what engine you have and the following:
    • Cylinder Placement
    • Firing Order
    • Cylinder Numbering Convention (which is which)
  • First, figure out where your pistons are. The repair manual/Internet should be able to tell you; for example, where your pistons are located in relationship to one-another. Usually cylinders like to stick together in 2's, 3's, and maybe even 4's. {diagram of a V-8}
  • It's a balancing act. Try to determine the best deactivation of cylinders by when they fire and their position. The rule-of-thumb is to avoid an uneven firing or placement of piston position.
  • One you have a basic idea of which cylinders to deactivate, and if you have an engine that has easily accessible fuel injectors that can be easily disconnected, then disconnect them and start the vehicle. (This author's vehicle has a squeeze connector that allowed easy disconnection of the injector [pic]). I do not recommend disconnecting them when the engine is running for safety considerations and the potential of arcing/shorting the injector connection. This author accidentally shorted out the fuel-injection system and was unable to start the vehicle. Having thought I burned-up the car's ECU, I thought I fried the car's computer. Luckily it turned out to be a fuse – it was replaced and the experiment continued.
  • Start the vehicle. You will probably get a check-engine light (CEL) as the vehicle is confused: "Why isn't cylinder #3 firing? I'd better rich-out the mixture to compensate and let the driver know". The CEL comes on. If you get a relatively smooth idle, you're in business. If it won't start, won't stay running with throttle input, or if you have harsh vibration, then I'd go back to Step #3 and figure out which other cylinders are to be deactivated. This hasn't thoroughly been tested, so it may take some trial and error.
  • If you do find a tolerable deactivation combination, the next step is to wire-in a switch somewhere inside the vehicle. I picked the rarely-used change holder to locate the switch, [Pic] as it was right where the wiring was coming through the firewall. The switch is a regular 2-lead variety toggle with basically an "on" or "off" setting.
  • Get an idea where the fuel injector wiring is located. It's usually in bundle or follows the length of the engine into a harness or more wires [Pic]. Examine each injector's wiring (some removal of piping or a rubber sleeve may be necessary). [Pic]. Each injector should have 2 wires: a ground and a positive lead (my ground was black with a yellow stripe). I found the same colored wire for each injector and determined that this was the ground wire. You will be cutting the ground wire at each injector, but not yet.
  • Get a feel for where your wiring will go. The next step is to drill a hole in the firewall to allow passage of wiring into the cabin of your vehicle. CAUTION: be mindful of what is on either side when drilling. Don't end up drilling into the brake master cylinder or something. Make some careful calculations.
  • OK, so we have a location for a switch, a hole for the wiring and a plan. Now comes the fun part – wiring. I'd recommend using solder and electrical tape, or crimp connectors to do it right. Just twisting wire and taping it will fail on you at the wrong time, trust me on this one.
  • Find the injector closest to the source of the ground [pic]. This will be our starting point and will provide a consistent ground. Cut the wire (leave enough room on either side to strip the wire and solder the connection) and route the source into the switch inside the cabin on one lead, through the firewall.
  • Cut the negative cable to each injector. Tape-off the source wire ends and strip the wires from each injector's negative lead. Tie the leads together {diagram} and route the tied lines to the other end of the switch through the firewall. Closing the circuit results in normal operation. Flipping the switch stops the flow of electricity to the cylinders – cylinder deactivation
  • Wrap tape around the wires through the metal hole or insert a rubber grommet into the hole. This is because the wires will most likely rub over time which can expose the wiring, short-out, etc. Use zip-ties or tape to seal the deal and keep the wiring away from moving engine parts.
Possible uses for this setup could include wiring all cylinders to deactivate on deceleration and partial cylinder running for light-load cruise. Further experimentation and suggestions on this site involve a pendulum device to work in conjunction with the deactivation system.
Some concerns could include uneven wear, hot and cold spots, and running too rich. A fuel management system may be indicated to lean the mix. If possible, the other set of cylinders could be wired to a separate switch to allow for even wear (switch to Cylinder Bank "B" at the next fuel up so those cylinders get used. Then at the next fuel stop, switch back to Bank "A").
Further experimentation and additional devices need to be adapted for consistent operation. Good luck, and please report your results.

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Old 08-27-2006, 06:01 AM   #2
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They generally deactivate the valves so those cylinders just act as air pumping losses.

Leading the perpetually ignorant and uninformed into the light of scientific knowledge. Did I really say that?

a new policy....I intend to ignore the nescient...a waste of time and energy.
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Old 08-27-2006, 12:26 PM   #3
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Originally Posted by theclencher
Earlier this summer I did my own displacement-on-demand experiments on my 4 cyl m/t MPFI Tempo. First I determined which pairs of cylinders when deactivated would still result in even power pulses. Then I simply pulled the injector wires off the 2 cyls and went for test drives. Engine started well, went through the gears well, cruised at 55 although it required much more application of throttle throughout (this is normal, as has been told by GM engineers in articles on their D-O-D). Engine vibrated more, but surprisingly not too bad! No idiot lights glaring or anything. So then re-activated the 2 dead cyls and de-activated the other pair to see if there would be an effect on noise, vibration, and harshness. There wasn't. Well, that it started and drove fairly well on 2 cyls was encouraging! Now armed with the knowledge that the deactivated cylinders are pumping air and therefore soaking up horsepower and decreasing engine efficiency, I deactivated the valves on the deactivated cylinders, eagerly anticipating to regain performance and efficiency lost from when they were pumping air. Now the dang thing won't run- it just baaaarely starts, then stalls right away- can't keep it running. Can't even do a test drive. Dang.

As long as I was in there, and it wouldn't go, I re-activated one cylinder and retested in a 3 cylinder configuration, just for giggles. It started, went through the gears, cruised, etc. BUT the vibs and sounds were most irritating. Even if it improved FE, it was too annoying to live with!

That is why we don't see D-O-D on 4 cyls- but I've seen it mentioned where it may be coming. No doubt it is under development. The key is to be able to start the engine on all cyls then de-activate only under light-load cruise conditions after all the accelerating and going through the gears is done. That is going to require more fabrication of special parts than I'm willing to do at this time.

P.S. The GM boys say uneven wear basically doesn't happen and it's not a concern.
Did you try hooking up a switch to remove power from the injectors? That way once you got up to speed you could just deactive the injectors and cruise until you need it again.
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Old 08-27-2006, 02:07 PM   #4
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You can take the rocker arms off those valves, eh?
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Old 08-28-2006, 07:36 AM   #5
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Also, if you aren't disabling the valves, it seems you are essentially pumping air through those cylinders into the exhaust stream of the running cylinders. I can see O2 sensor responding and causing the ECU to enrichen to (over) compensate. If you do interrupt the valves, you'd solve that problem only to change the volume of air coming in through the MAF maybe causing the ECU to lean it out too much. Maybe.
Reality is merely an illusion, albeit a very persistent one. - Albert Einstein
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Old 08-29-2006, 07:14 AM   #6
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i dont think its worth it. you still have all of that reciprocating mass. there is no savings in work.
don't waste your time or time will waste you
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Old 12-22-2006, 09:19 AM   #7
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What if you were to merely block off the ports on the intake manifold by sandwiching a steel plate between the intake manifold and head rather than disabling the valves? In theory, this should create a vacuum at the intake after just a few revolutions, a vacuum is a lot easier to compress than atmospheric pressure, and there would still be no fluid flow to cause pumping losses.

Personally, if I could disable two of four cylinders easily I wouldn't bother with variable displacement. My car has 120 hp with 4 cylinders, and 60 hp would suit me fine.
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Old 12-25-2006, 11:42 AM   #8
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My car has 135bhp with 4 cylinders, and I have been doing some interesting experiments.

I can use the LPG changeover switch to deactivate the injectors to two cylinders (I did this when trying to find out why my mileage computer wouldn't
recognise the injectors). I made sure the two cylinders I chose were ones that are opposite to each other, so that it isn't running more unevenly than it needs to. I don't think it does anything for economy (but I will check this when I get my SuperMID working), but some 'fun' things are:

(1) If you floor it at about 2500rpm, the turbo will go to full boost, but, there still isn't very much power. Then, if you switch back to 4 cylinders, you get a sudden massive power boost
(2) When at 4000rpm on full boost, the fuel is probably running at a 1:11 fuel/air ratio (quite rich). Normally, the hot partially unburnt fuel is just ejected from the exhaust, and has cooled down by then. However, if you have two cylinders pumping air, you get a certain amount of partially burnt fuel being introduced to nice clean air from the two deactivated cylinders. If you then suddenly let go of the accelerator, you get a nice flash + bang from the exhaust!.

None of the above are good for economy and have probably brought my tank averages down a bit . However, I like the idea of the 'air springs' and may see if this has an effect in the future as well.

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Miles displaced by e-bike since 1 Jan 2008: 62.6 (0 kWh used)
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Old 12-26-2006, 01:25 AM   #9
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Originally Posted by Bruce
What if you were to merely block off the ports on the intake manifold.
You must block off both intake and exhaust ports and remove the spark plug.
Run the plug holes via threaded pipe into a heavily muffled air cleaner element to stop the sucking sound.
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Old 12-26-2006, 05:17 AM   #10
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Originally Posted by theclencher
No! Leave the plug in or else ya still gots the pumping losses.
If the plug is left in on the downward piston stroke you will create a vacuum above the piston which will draw air from the crankcase into that space.

Piston rings are not good at sealing under these conditions, that is why rings have UP markings.

On the up stroke it will try and compress that air.

Its better to leave the plug out so that no vacuum can form above the piston and no air is compressed.

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