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Old 09-10-2007, 10:34 AM   #1
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Fuel injector cut....

Has anyone on here ever thought about just shutting off injectors while cruising? I mean, the new v8 trucks and stuff do it to save fuel, why can't anyone else with fuel injection?
You'd have about half the power, and use half the gas. It doesn't take that much power to cruise at say 65mph, and 2cylinders should be plenty to keep you going..... unless you run into a big hill.....

Only thing I can see is that 2 cylinders will just be pumping air and the other two firing, so the 02 sensor will think its lean, and richen it up a bunch. But what if you use one of those o2 sensor controller things to fool the ecu into thinking its running correctly?

any thoughts?
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Old 09-10-2007, 12:02 PM   #2
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A few members have tried it, none with success, if I recall. (But not with the O2 sensor mod)

Dig around with the forum search tool and you'll find several threads on the topic.
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Old 09-11-2007, 08:53 AM   #3
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the problem with that idea is that the piston will still move up and down. each time that it moves up it is compressing air. that is wasting energy that you have put into the system. the new trucks and cars that shut off cylinders have the ability to leave the valves open so there is no pumping loss.
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Old 09-11-2007, 11:47 AM   #4
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Quote:
Originally Posted by boofighter View Post
the problem with that idea is that the piston will still move up and down. each time that it moves up it is compressing air. that is wasting energy that you have put into the system. the new trucks and cars that shut off cylinders have the ability to leave the valves open so there is no pumping loss.
Actually, no. The system CLOSES the valves when in operation. The system also increases throttle when it activates so the power available does not change when the 4 cylinders are deactivated. If the engine requires 100HP to move the vehicle before the cylinders are deactivated, then the computer adjusts throttle position so that the engine is still making 100HP after deactivation. According to the theory behind it, closing the valves means the air is compressed which takes energy, then when it re-expands it puts almost all the energy used to compress the air, back. Here's a pretty good article on it.

Just cutting power to half the injectors will make a mess of things, as you'll be dumping "clean" air into the exhaust. This will mess with the O2 sensor. The computer won't understand what's happening and might just shut the engine down.

I'd think that they would save more fuel by adding a third valve that let the piston force air in and out of a larger chamber to prevent load on the engine, but that would just overly complicate the system.

What I really don't like is how the system uses oil pressure to control how it operates, at least on the GM system. This means the reliability of the system depends upon the maintenance habits of the general populace. And we all know what that means, oil changes once a year whether it needs it or not, using that quality China Mart brand oil.
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Old 09-11-2007, 08:13 PM   #5
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I ran a 4 cylinder 2.3 turbo Ford on 3 cylinders with one injector unplugged one time. There was a lean spot in the calibration. It literally melted the pistons and valves in the three running cylinders. Well I stopped after I got a hole in one piston but the engine was destroyed for all practical purposes. Turbo engines can make a lot of heat if not at the right fuel mixture. This is an extreme case but is an example of how unplugging an injector or two can really go wrong.

I bought the plans from a guy who ran a Honda this way. He sold plans for a pendulum switch that turned the injector on going up hill and turned it off going down hill and on the level. He managed around 87 mpg in a contest. The plans were pretty basic.

I ran a V-8 on 4 cylinders for about 5,000 miles. I thought that compressing the air would be a mistake at that time. I left the intake valves out of 4 cylinders, every other cylinder in the firing order. The manifold was divided so it just ran on 1 barrel of the two barrel carb. I had a plate blocking one side. Moving that air from cylinder to cylinder was a big mistake. The engine could not produce usable torque above about 4500 RPM. If I ever try that again I will just pull the rocker arms or push rods. That would be a lot easier. One would need to gaurd against a lifter coming out of the block as this would make a large hole in an oil galley. I would rate the overall result as a bit disappointing. It was about a 10% increase in mileage.

It is not exactly the same but on heavy duty diesel engines the exhaust valves are manipulated for so called Jake brakes. The air is compressed then the exhaust valve is opened near TDC. An 855 cubic inch engine can absorb hundreds of hp in this mode. For development purposes an engine was set up to drive another engine. I was told the driven engine was absorbing 400 hp. This is just a silly story to emphasize that it is quite important how one deals with the non running cylinders, but we already knew that.
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Old 09-13-2007, 04:58 AM   #6
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Well I hooked up a set of 2 relays to the ground side of the injectors, and put a switch in my car, so that when I activated the relays, it would shut the signal off.
not enough power to start you off, but it was enough to keep you moving at 65-70mph in my accord. On big hills, I had to put it back to 4cyl, but then right back off. Did this all week, and just filled up this morning and I got a 1.3mpg increase over my base of 32mpg.
you could tell the engine was dumping fuel in the cylinder, cause it was running rich, and bogging really bad.
I'm going to try to build one of those things this weekend with my buddy to fool the O2 sensor so it doesn't richen it up when it senses all that clean oxygen.
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Old 09-15-2007, 07:34 PM   #7
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I think the only way it will work is if the computer is also in open loop. Cutting the O2 sensor output will probably do this. Then the computer will only base the amount of fuel injected on the other sensors.

As long as the throttle is open, the drag caused by compressing air is minimal because it acts like a spring. Thus the compressed air will return the potential energy by pushing down on the piston during the power stroke.
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Old 09-15-2007, 08:06 PM   #8
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I was just thinking about that tonight.... about how all you guys said that the engines that do this from the factory disable the valves, so that it works on an "air spring" well... regardless of whether the valves are working, or not, it will still be a spring, on every other rotation. the other rotations, it will just be "free wheeling".

I'm having my friend come up tomorrow to help me put together an o2 sensor controller, so I can trick it into thinking its running properly. This will help out tons
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Old 09-16-2007, 07:25 AM   #9
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Help me out if I'm wrong guys.

Does the first O2 sensor(precat) control the fuel?
If this is the case, put an O2 sensor bung on the exhaust manifold at one of the running cylinders prior to the collector area.

Keep us updated, this will be my winter project on my zx600.(running 2 cylinders)
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Old 09-16-2007, 08:03 AM   #10
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yep, the first one controls the mixture....

I could put a new bung in the one of the runners, but the stock exhaust manifold is cast, and I don't have the equipment to weld to it.
Otherwise, that would be a good idea!

If I get a cheap mild steel aftermarket header (let the engine breath easier, gain some power, and hopefully better FE), I may just do that.
But today my neighbor and I are going to get the parts to build that 02 controller thing....

I still need to find a way to trick the computer into thinking that the other 2 injectors are still firing so it doesn't throw a code.... any suggestions? I'm not 100% sure, but I think the car goes into a 'limp home' mode when it throws that code too, cause it won't rev above 4k rpms after this.

EDIT:
Just went and read the codes:
Throws a "Fuel Injector System defective circuit or unplugged / defective fuel injector" code, and a "Fuel Supply System defective or malfunctioning fuel supply system"
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