Cylinder Deactivation
 

Author: Harrell, Rick
Publication:www.gassavers.org
Date:11/16/2005
Background:
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.
Hypothesis:
Deactivating cylinders in low engine-load situations and/or zero-throttle input will yield higher fuel economy.
Results:
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
Disclaimer:
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.
Implementation:

• 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.

Conclusion:
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.

They generally deactivate the valves so those cylinders just act as air springs...no pumping losses.

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.

You can take the rocker arms off those valves, eh?

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.

i dont think its worth it. you still have all of that reciprocating mass. there is no savings in work.

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.

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.

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.

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.

I stand by my last post.

From what I have read , auto manufacturers deactivate the cylinder after the firing stroke and use the exhaust gas in the chamber as an easily compressable spring.
This works fine , for a while.
In time the exhaust gas leaks out (valves and ring leakage) and it starts to compress air , then the advantage is gone., and now you start loading up the other cylinders.

My answer was in reference to Bruce's question ?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??

As Bruce would be vac'ing + compressing air immediately it wouldn't work.
My suggestion to remove the plug to allow air to vent in and out easily would provide an improvement by not trying to compress the air.

But as far as existing cylinder deactivation is concerned , with only a 5 to 10 % increase in FE it is hardly enough gain to warrant such a complicated system.

Air movement does incur a pumping loss, but the biggest contributor, what people talk about wrt gassers, is the pressure difference between the crank case and the closed cylinder as it moves down. At low load there is less air in each cylinder, which means the delta pressure between the crank case and cylinder at the bottom of it's stroke is significant, with the crank slowing significantly before the air/fuel is ignited because of this.

Gammy is right, although I don't think the exhaust and intake valves need to be blocked off. Just remove the plugs from the cylinders you don't want to run and make sure there is no fuel getting to them. Actually, leaving the exhaust/intake valves functional would be an advantage, since this lets in more air initially, so as the piston moves down there's already more air in, so less has to come through the spark plug hole which may reduces any losses from the smaller (but not static) pressure difference between cylinder/crank case while the piston is expanding, not to mention that more air will get in because the other two pistons need more air/fuel to do the same amount of work as four did during the same time span. All in all, I think you could easily see a 20% increase in FE if this worked. Do eeet! :D

Something else I just though of, get a normal gasoline PFI engine from the junkyard, and set it up for TBI/SAFI (megasquirt or whatever). This way, you can put a solenoid on each of the fuel injection holes that will open whenever you want. At a cruise you can fire one cylinder per rotation sequentially while opening the other cylinder's solenoids/cutting fuel to them. I'm not sure if this would result in some funky vibrations, but since you can fire a different cylinder/combo of cylinders each engine cycle, maybe you could work something out for best fuel efficiency/least vibrations.

Anyway, as for your first experiment, cutting fuel to two cylinders, you should see some increase in mileage. Removing the injectors from those holes should net a larger increase in efficiency. If you had a nice long stretch of road next to a gas station where you could go at some low speed in top gear this would be a great experiment, checking the increase in efficiency after fuel deactivation and then after pulling the spark plugs.

Think about it this way. Diesel engines are already BTU corrected by the EPA for mpg figures. And in the same car with the same transmission diesels get ~30-40% better efficiency, partially because compression ignition is a little more efficient, but mostly because the throttle is always wide open. In fact, on most there isn't a throttle. Diesels always suck in enough air/exhaust gasses to fill up the cylinder totally, so when the cylinder is at the bottom of it's stroke, the pressure in it is about the same as the crank case pressure. But in gassers, there needs to be a correct air/fuel ratio, so there can only be so much air drawn in, which is metered by the throttle, cam duration, and valve size. Since most of the time, the car needs much less than full power, there isn't a full amount of air drawn into the cylinder, and when the cylinder is at the bottom of the stroke, the pressure in it is much less than the pressure in the crankcase. The entire time it was traveling down, if the pressure is greater in the crankcase, then this is effectively resisting the cranks forward momentum, and reducing efficiency.

Going to the variable displacement idea, if the engine only needs 20hp at 65mph, by only using say, four out of eight, the throttle can be opened wider since those active cylinders need twice as much air to burn twice as much fuel (or remain closed and act as springs if vibrations are a problem), and since the other four aren't burning any fuel, they'll suck in twice as much air too, w/o any probs, and the difference in pressure between the cylinder/crankcase will be much smaller with more air in all the cylinders. I think the biggest hurdle was making the transition and operation with fewer cylinders smooth/reliable.

One more example is the Atkinson cycle. Toyota keeps the intake valves open longer so that a larger portion of air can be pulled in, then closes them once the cylinder has moved up and pushed enough air out for the air/fuel ratio to be correct. By letting more air in the pressure difference between the cylinder/crank case is smaller, so less negative work is done.

That's a typo, I meant the intake valve would let in more air because the throttle is open wider. To allow the two operating cylinders to make double the power you need double the air so you could go the same speed compared to all four firing at that speed. Bleh, that's a mouthful. I'd love to screw around with this, but I only have a carb'd pickup and a diesel that are mine to play with. ;)

Huh? I meant that as an experiment with an engine retrofitted with throttle body injection. You are using MPFI, one injector per cylinder, correct? The point of my brainstorm was to have solenoids in the injector holes and fuel/air coming from the TB to allow for selective cylinder deactivation in a certain pattern. All you should need to do is disable two of the injectors so they don't fire, which should be the largest increase in efficiency since you'll be cutting pumping losses in half. And by removing the spark plugs from the two cylinders where fuel is deactivated, this allows the pressure in the cylinder to always ~equal the pressure in the crank case, even if you're at a speed where the other two cylinders aren't drawing as much air in as they could. The first step should increase efficiency the most, and removing the spark plugs should help a bit more.

Wrong.


https://www.fueleconomy.gov/feg/tech_engine_more.shtml
Potential Efficiency Improvement: 7.5%

https://ezinearticles.com/?Cylinder-D...ing?&id=226193
Although typical gains range in the neighborhood of just 5-7%,

https://www.worldcarfans.com/news.cfm...r-deactivation
Preliminary testing of the 2007 Chevy Impala equipped with the 3.9L V-6 with AFM indicates an estimated 20 mpg in the city and 29 mpg on the highway ? improvements of approximately 5.5 percent and 7.5 percent, respectively.

https://www.edmunds.com/advice/specia...1/article.html
On the regular EPA mileage test, DoD delivers fuel economy improvements of 6-8 percent

https://en.wikipedia.org/wiki/Active_Fuel_Management
EPA tests show a 6% to 8% improvement in fuel economy

https://www.auto-report.net/j30avcm.html
While such cylinder deactivation strategies are expected to improve fuel consumption by around 5%

https://autospeed.drive.com.au/cms/A_2618/article.html
By keeping the intake and exhaust valves closed, it creates an ?air spring? in the combustion chamber ? the trapped exhaust gasses (kept from the previous charge burn) are compressed during the piston?s upstroke and push down on the piston during its downstroke. The compression and decompression of the trapped exhaust gasses have an equalising effect ? overall, there is virtually no extra load on the engine.

https://en.wikipedia.org/wiki/Active_Fuel_Management
In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring.

https://www.carterdodgechrysler.com/n...dge-magnum.htm
Deactivation occurs during the compression stroke of each cylinder, after air and fuel enter the cylinder. Ignition then occurs, but the combustion products remain trapped in the cylinder under high pressure, because the valves no longer open. No air enters or leaves. During subsequent piston strokes, this high-pressure gas is repeatedly compressed and expanded like an air spring,

I think theclencher's take on mileage increase is accurate. The EPA tests have the car bouncing around in terms of speed, so who knows how often DoD is actually activated. I'm guessing that a four cylinder with ghetto DoD could see as much as a 20% increase cruising at 45-55mph because it'll always be on unlike commercialized systems by GM, etc... that are designed for the overall driving experience.

From one of the articles Gammy posted

The highest figure that I saw was 20% improvement and that was on an suv with a huge engine at steady highway speads under ideal conditions.
It dragged it up to 22mpg , which is still S&/T FE.

I never saw any 20% improvments when talking about small 8's 6's ,,and 4s.

For a budget deactivated gheto car why not take out the piston and rod , block the ports and add ballance weights to the crank pins.
Then you have real cylinder deactivation with far higher gains.

Because it's easier to just kill two injectors, have two cylinders firing that require twice as much air from the throttle, with the two dead cylinders getting twice as much air as well... Compared to pulling apart the engine to have what would a bit more efficient (no friction from movement and no pumping losses from pulling the air in/pushing it out, even though these pumping losses are small compared to the usual pressure difference imo). I think killing two injectors and removing those spark plugs will see a far bigger increase over stock compared to the increase from putting weights on the crank pins/blocking it off over killing two injectors and pulling the plugs.

Granted, how much pumping losses are reduced depends on gearing, cylinder size, etc... But if large SUV can see a 20% increase at a steady cruise, I don't see why two cylinder operation for a large four cylinder car wouldn't result in similar economy gains at a steady speed. And, unlike the usual DoD systems, this one can be activated/deactivated at will by putting switches on select injectors. I think more than a 20% increase is possible because the FE minded driver can always have the system on.

We need someone with a scanguage or supermid to figger this'un out! :D

Your dreaming. !
Removing the mechanical parts and rebalancing is the ulitimate solution if you wish to take that route.
You have no frictional or pumping losses whats so ever.
How can simply removing the plug off an injector equal that . SHEESH.

ogl: you are not alone in the issue, but you have covered all points i would try to make haha.

I never said it will equal that. But it will be the greatest increase w/o pulling apart the engine. By cutting fuel to two cylinders we cut pumping losses in half, which should have the biggest impact. We can then pull those two cylinders/balance, and remove friction losses, which are small at the usual rpm a fuel economy minded driver travels at, and pumping losses, which may still be larger than friction even after they were originally cut in half. But, by pulling the spark plug, we would remove almost the same amount of pumping losses versus blocking off the cylinder, since pushing air in and out isn't what causes inefficient low load operation in gassers, lack of manifold/cylinder pressure is. So, for the record, I'd go with cutting fuel to two cylinders and that's it. But I think pulling the plugs would be a nice compromise since they would cut pumping losses almost in half again, w/o pulling the engine apart. I mean, how much do you think we'd gain from halving the friction at 2k rpm? I'm guessing not nearly as much as almost quartering pumping losses.

This engine for example, is probably around the 500g/kwh area at 55mph in top gear.
https://www.v6performance.net/gallery...0805_Fig11.gif
By running off of half the cylinders, we double the torque made by the other half, and double the air flow to all, probably going from the 500g/kwh to the 300g/kwh area. Now, we can also pull out the cylinders that aren't firing to cut the remaining friction and pumping losses in half, but if the minimal BSFC is ~240g/kwh (actually less since we'd only have two cylinders), how much more of an increase in efficiency are we gonna see going from ~300g/kwh?

Here's some more on DoD.

My eyes must be playing tricks on me then , because what I read in that article was --

¨GM estimates fuel economy savings of 8% when driven on the standard fuel economy test routine and up to 25% increased economy for some driving conditions¨

25% under some conditions , is not 25% gain.
The average FE gain is as clearly stated - 8%.

Focussing on that 25% is just the same as believing some of those incredibly high instantanious reading ones in here get on their Scangauges.

Great numbers , , just not reality

But a DIY economy minded driver who puts this system in is not going to drive according the the EPA driving schedule. And the system, which is very touchy and switches on/off quite a bit, will be on most of the time. The point I'm making is that if GM says the average EPA benefit is 8%, and the max from the system is 25%, then someone interested enough in economy to rig their own version will probably use it most of the time and see way more benefit compared to the EPA cycle computer controlled benefit that switches on/off a lot and isn't on as much. I think a 20% increase in FE isn't that hard to imagine when some people here see upwards of a 50% increase just by changing driving habits. I mean, what you're saying is that those numbers won't reflect reality, which is probably true for GM's version, but I think they can if someone here is driving to take advantage of their own DIY system.

have you taken a look at how honda works their cylender deactivation? it's simaler to how they do there variable valve timing, only with differnt rocker arms, the first time I held one of honda's heads with cylender deactivation in my hands I was confused, then I realized what it was.

I'm checking it out now. I found this on cylinder deactivation for a CBR1100 prototype , and it looks like Honda is being way more aggressive with their system.

Just pulling the fuel for say, two out of four cylinders won't have as big of an effect because there are still the two inactive cylinders pulling in air, but I really think cutting fuel on two out of four cylinders on an inline four could result in a 20% increase in mileage. Here's something else to chew on

So with the air springs/closed valves, pumping losses drop by nearly a half, halved, aka 75%, with the difference probably being increased pumping losses for those cylinders that are carrying a bigger load, so 65% real world. I'd wager that the DIY version via a fuel cut to two cylinders could reduce pumping losses by up to ~40%, and power would be available by turning the two injectors back on from the cab. Now there's also the question of whether or not the engine/mounts can handle this... I wonder if the variable displacement engines share the same bottom end as their "normal" versions?

Going back to the bike, if something like a twenty year old CB650SC can pull ~45-50mpg in normal riding, and probably ~70-80mpg in fuel efficient riding, it may be possible to run ITBs/SAFI and have a bike that can run low 11s quarter miles while getting nearly 100mpg@55mph with two cylinders deactivated.

I think you guys may be missing the point WRT hypermiling...an _automatic_ cylinder deactivation, like an automatic transmission, won't affect fuel economy as well as a manual one because the cylinder deactivation will happen at the wrong time to have the greatest impact on efficiency.

Automatic cylinder deactivation is designed to reduce fuel consumption only while cruising, not during acceleration. If you're using 10% of your V4's available power instead of 5% of a V8, that's not going to give much of an engine efficiency improvement compared to the 80% vs 40% you'd get
during acceleration. I'd expect GM's ECU would activate the deactivated cylinders long before you'd get to that point.

For cylinder deactivation to have the greatest impact on FE, the deactivated cylinders should only be activated for emergency acceleration (and perhaps starting, as suggested above). Only the driver can determine when emergency acceleration is needed, not the ECU.

As a side note...my first (and previous) car was an `78 Chevy Malibu we bought in `85 with a (carbureted) 305 V8. On its 2000 mile trip home, it averaged about 20 MPG. Several months after we bought it, we had the engine rebuilt. It had a soft cam and a few of the lobes had worn completely off, so the engine had effectively only been running on six cylinders. After the rebuild, which effectively reactivated all the cylinders, the best FE I ever got was 15 MPG.

As I said, I'd rather just make do with 60 HP instead of 120 all the time and just avoid situations that require emergency acceleration (e.g. pulling into a short gap in fast-moving traffic). The extra time spent idling while waiting for a longer gap would be more than offset by the greater overall efficiency.

you are right and an economy minded driver doesnt drive a v8

Reviewing this thread again, and thinking about what it would take to effectively reduce a 4-cylinder PFI to 2 without major modifications, I've reached a few conclusions:

- If you want a 4-cylinder engine to start on 2 without major modifications (ie. tearing the engine apart), you need to allow fluid to freely move through the cylinder, as with an unmodified valvetrain. If fluid is going to move freely anyway, making it move as freely as possible would reduce the losses. Hence, removing the spark plug and perhaps the injector makes the most sense for the small-time DIYer. If you can tear apart an engine, removing all the extra parts for the dead cylinders makes the most sense, and this has been done in the past.

- If extra air is introduced into the exhaust, the O2 sensor will sense it and richen the mixture to compensate. This would probably negate any net savings in efficiency, so it appears essential to block the exhaust ports -- either the valves or the manifold ports -- of the deactivated cylinders to keep fresh air from reaching the O2 sensor.

Any thoughts?

Good point about the behavior of the O2 sensor, probably why most manufacturers use the air spring approach. Obviously, running in open loop mode would avoid a really rich condition, so killing the O2 sensor and injectors may be required. Also, the ECU may only richen the mixture up so much, so the increase in efficiency could still be greater than the decrease from a rich mixture, or the ECU may even automatically drop into open loop when the injectors are turned off. This would be a great project for someone with a flashable ECU/SAFI and a SG.

I think you mean marginally more power. ;)

Depends on what you mean by pumping air in and out because we have two situations that describe that.
-Just killing fuel to two injectors.
-Killing fuel to two injectors and pulling the spark plug/injector.

According to Honda, aggressive cylinder deactivation results in a 30% increase in fuel economy, which corresponds to a 65% reduction in pumping losses. They do this by deactivating two cylinders, which results in the other two pulling in twice as much air, to make the same power, and a halving of pumping losses, as well as the closure of the two deactivated cylinders, which theoretically halves pumping losses again. Ideally, we'll see a 75% reduction in pumping losses, a half halved. Real world, those two cylinders have to pull in more air, and the two closed ones aren't perfectly closed, so we see a 65% reduction in pumping losses.

So, if we just cut fuel to two cylinders, we theoretically halve pumping losses, and realistically cut them by ~40%. We then have two choices...

-Close the cylinders completely.
-Open the cylinders as much as possible.

If we close them we know we can see a ~65% reduction in pumping losses, but, most cars would need a very high idle to run like this, or different EFI routines (turning the cylinders off past idle) to have the car run in this state. You said the Tempo would barely start, then die. It may start and run if you raise the idle enough, but then again, what's the point of halving pumping losses just to idle at twice the normal speed. That's going nowhere fast. So imo, closing the cylinders is best left up to a manufacturer.

We can also permanently kill the fuel to the two cylinders, and pull out the spark plugs/injectors. This will reduce pumping losses from those two cylinders, but not eliminate them like the air spring system would. They'll still pull air in, and push it out. But, if the two active cylinders still aren't filling completely when cruising at around 40mph in top gear, the two that allow free passage of air will be.

The reason why gasoline engines are inefficient at low loads is the difference between cylinder pressure and crankcase pressure. Diesels don't have this since the cylinder is always completely filled, so they get much better mileage at lower speeds. Opening the spark plugs/injectors allows the pressure to equalize in the two cylinders that aren't active. While pulling air in, and pushing it out, does result in pumping losses, these are very small, and akin to what diesels see. So, I'm guessing that w/o plugs/injectors, pumping losses may be reduced by ~60%, compared to 65% with a totally closed cylinder.

The thing is, if we're going this far, we might as well just pull the pistons to get rid of friction too (which should result in a greater than 30% efficiency increase). So for cylinder deactivation (a bit less than 20%), I think an all or fuel cut are the best approaches. The thing I want to stress is that when people talk about pumping losses in gasoline engines, they usually mean the difference in cylinder/crank pressure, not the movement of air in/out. While both result in losses, the pressure difference is why gasoline engines are so lousy at low load. It's also why diesels are good at low load, since they always pull everything into the cylinder they can.

Temponut, did you get black smoke when you pulled two injectors?

you could easly fix the problem with the o2 sensor by getting an exaust header that has an o2 sensor in one of the exaust streams that is getting fuel, the computer assume that all 4 cylenders are getting the same amount of fuel because it's opening each injector the same amount, so it can get by with monitering just one cylenders exaust.
https://www.jaydm.com/assets/dc/4-2-1ss2p.gif

if you want to make this a perminet modification, why not just swap in a smaller engine? it would run alot smoother, but I see having it set up kind of like the vtec-e system, where it operates as a more efficent engine 95% of the time, but when you ask it for more power, how the engine operates shifts, and the power is there.

Well yeah, a turbocharged 700-1000cc engine would probably work great in my car, but it takes a lot more time, money, effort, knowledge, etc. to put in, and it'd ruin any resale value of the car (although if my last car is any indication, I'll be the last owner of this one.) The conversion cost isn't justified unless you drive a lot, and I don't -- my current commute is only 16 miles.

That is a good thought about O2 sensor placement. It may already be on one cylinder, in which case I may be able to just pull the injectors and plugs on the opposite two. I'll need to take a look.

Will removing the plugs from two wires damage the electronic ignition, or would it be better to plug them back in and cap them?

- Bruce

There's a lower limit for doable (no custom motor mounts etc) small engine swaps and I'm trying to figure out whether a gasoline engine can be modded relatively easily to get the same mileage as a diesel during the same driving conditions. Would it better for the average driver to just swap in a diesel, or can they see the same mileage for way less by modding the gasoline engine they have for lean burn/cylinder deactivation?

I believe I've already spotted a car in the Garage where the owner swapped out a gas for diesel and had a huge increase in FE, but I can't remember whose. I know I've seen at least a couple with swapped engines.

A `92 isn't new enough to use a Scangauge...did you verify the decreased FE at the pump?

I'd expect more throttle would be needed, but that doesn't necessarily indicate lower efficiency...a good example is lugging an engine at low speed (great efficiency, and it takes a lot of throttle).

It could be because of the ECU going into closed loop... The difference in mileage for something like a normal versus lean burn civic is ~20% at cruise iirc. So if going from ~15:1 to 17-19:1 allows for this, a richer default map at 12-13:1 may wipe out any gains made by only running on two cylinders. In order to find if I'm completely full of it we'll need an engine running on half the cylinders via a fuel cut with an oxygen sensor in one of the exhaust runners of a running cylinder and a SG to get accurate back to back runs and determine if the ecu is in closed or open loop mode.

I didn't know about the previous post on the subject, but found it today:

https://www.gassavers.org/showthread.php?t=48&page=3

Bottom line was 24.3 MPG with fuel cut to two cylinders vs 26-28 normally.

- Bruce

Running it in a higher gear just to avoid vibrations defeats the purpose of the experiment. That combined with richer running, and it's no wonder the mileage was worse. At the very least, we need a couple runs at the same rpm, ideally with the O2 sensor in an active exhaust runner.