Cutting Power To Injectors (Highway Cruising Gas Saver)

[Beodude123]

I saw this on another ZX2 on some EcoMod website I think, but I think it was a pretty cool idea.

He used a switch connected to the injector power to shut the injectors off. Would this work? I know some cars do shut down cylinders when cruising, but I think they do more than just shut the injector off.

So would this work? I know it would kill power when cruising, but that's not really a big deal since it doesn't take a lot of power to do. Obviously I won't be able to do it to the cylinder with the 02 sensor in it, but are there any specific cylinders I should use?

Most importantly, will I do any damage doing this? Last thing I want to do is mess up my car. I don't see why it would hurt, but you never know.

Basically all I would do is splice in a switch to the injector power line, and turn them off when I'm cruising. Thoughts?

[xtremecaraudio]

I think you would also have to make sure that the spark is not firing in that cylinder as well. I know being lean is really bad, but no fuel I guess I'm not quite sure about.....

[Beodude123]

Yeah, I know about leaning it out being bad. The reason that is bad is because it gets too hot. If there is no fuel to burn, I don't see why it would be a problem. It would pretty much pump air (I think).

[capitalcrew]

If you cut full power to two injectors you'll run on two, obviously. Just make sure that you don't do two fires in a row, do every other. That way you don't go uber long without a fire then have two quick ones.

[Beodude123]

Yeah, that's what I thought. I figured cutting 1 and 4 or something like that. I know I can't do the one with the 02 sensor, so I guess I'd have to do two of the others.

[xtremecaraudio]

There will still likely be a lean condition everytime you hit the switch to turn them off though.

[Beodude123]

If I turned the car off, turned the injectors off, then started it again, I think it would be good.

[LiveWire]

I'm not sure what that would gain you. If the dead cylinders are still pumping as much air, then you would not go lean. If a loss of scavenging causes them to flow less, then the difference is flowing through the other cylinders and you would be lean. Maybe you could figure out by how much and put a resistor in the MAF wiring that is bypassed normally. Meaning you flip the switch to drop the injectors and it lowers what the MAF sees at the same time. You shooting out ideas.

[mechtech]

There a a few cars nowadays that cut cylinders on the highway. They can work well if you have a massive engine.
The old systems [remembers GMs shitty V8-6-4 ?] were horrible.
The new ones are quite complicated and interrelated.
If you cut our cylinder's injectors, the remaining cylinders will have that much more work to do. You are also deeper in the throttle, and have less ignition advance, and less gas mileage.
I am being surprised at how much gas can be saved by slowing down on the highway. I would not have thought it was so much, but people that do tests and use Scan Gauges show that from 55 to 65 to 75 the gas use is substantial.

[iceracer]

The injectors are cut off in a closed throttle coast by the ECM until a low rpm is reached.
The idea of a switch was thought up by a Hipermiler. Think of what a pain it would be for daily driving.
You only have a lean condition when there is some fuel to burn. With the injectors shut off there is no fuel to burn.

[Twiggy2cents]

....random fact of the day a misfire can cause a lean code being that there is unburnt oxygen in it...

also displacement on demand engines vary the cylinders

if you have a header it reads o2 off one cyl so you would be fine

#2nd random fact: when the engine over heats it cuts just fuel to alternating cylinders to run them as an air pump to cool down the engine

you could do it and try, maybe just hook a switch to one inj and try it i guess. but like mech said its for bigger engines. Have you tried leaving a spark plug off and starting the engine... just at idle it looks like its gonna die


#3rd random fact only two cyl's fire in one cranshaft revolution on a 4 cyl (hence the idle vibrations), 6 cyl is 3 every rotation, 8 is 4 every rotation, 10 is 5 every rotation. now a 5cyl volvo is crazy that is 5 every 720 degrees... think that one out in your head...

im done blabbing on with useless info

[Tygen1]

I'm with Mech, just slow it down and enjoy the ride. My average MPG went from 30.5 at 75mph to 37.5mpg at 60mph and no A/C. I was blown away by the dramatic increase. No need for silly tricks when slowing it down works so well.

[Beodude123]

I know going slower helps a lot. I'm just trying to figure out another way. If I go 60 and cut two cylinders, it would be even better!


But as far as drag on the other cylinders, I can feel you on that. I know that the other two are going to have to work harder to make up for it. But at the same time, an engine only operates around 30% efficiency or something like that right? Since most of the heat is blown out the exhaust, cutting that number in half should help out a lot. I know it won't be half, but I imagine it would help out a lot.


I'm going to do it, and log some numbers. Next tank of fuel, I'll be good. 60 mph, slow acceleration, and no "fun time" going on the on ramps. Nice and easy for me. I'll get a reading on that, then I'll do the mod, and give that a try. Same driving style, same everything. Then we'll see what happens.

[iceracer]

I recently improved the mileage on my Jeep by 2mpg by driving 65 instead of 75. that thing has the aerodynamics fo a brick.
Trip didn't take that much longer either.

[Twiggy2cents]

also it will try to adjust to fix the misfire you will be creating

[Beodude123]

Yeah, I was thinking about that when I was working on the 2000 today. On a stock manifold, it would throw out a lean code, since it would be pumping half the gas, and all of the air. But since the aftermarket manifolds read off of one runner, it wouldn't be a problem.


Besides, without a knock sensor, how would it know that the cylinder didn't fire?

[Twiggy2cents]

a knock sensor picks up pinging.... the pcm can monitor abnormal input from the crank sensor

[Beodude123]

Ah, right. It would notice a lack of force I guess?

[CT9A]

you might be able to fool the computer with sct... but if you had sct you could just tune the car to run Lean when cruising on the high way. You would probably get the same amount of improvement in gas mileage.

[mechtech]

Also remember that the MAF reads flow. Since you are not de- activating any valves along with the fuel cut, it will read higher than it should.

[Beodude123]

Right, but so long as the A/F is reading properly, would it try to compensate for anything?

[mechtech]

As you can tell, I am not a fan of simply cutting the injector's power. It really has to be integrated.

[Beodude123]

I know man. It's not really that big a deal. I wanted to see what people thought of it. Just trying to stir up the pot a bit.

[Stretch]

I don't know man. I've seen that my KVT5 processor is programmed to command a 1.0 Lambda for afr at low rpm/load. That's full on 14.64:1 which is about as lean as i'd want an engine going. I know that this doesn't necessarily mean that every ZX2 out there is programmed this lean, but that's not the point. Question is .....

Do you know what your car is really outputting for actual low rpm/load afr right now?

If the answer is no then you should probably be looking at other ideas.

[Beodude123]

you might be able to fool the computer with sct... but if you had sct you could just tune the car to run Lean when cruising on the high way. You would probably get the same amount of improvement in gas mileage.

If you lean it out too much, it can lead to detonation. Granted it's low throttle and load, but I imagine it can still happen.

[mechtech]

At low throttle opening, lean won't hurt your engine. It will run shitty, but it won't hurt at all. How can it?
Even at full throttle, everyone says it will burn up the valves, but I don't think so.
Maybe in some racing situations, or with boost. If you are using the fuel to cool an engine at the edge, maybe, in other words. It will run worse, for sure, but I have no problems with lean for engine damage.

[LiveWire]

The bulk of the extra air will still get pumped through the dead cylinders so the computer may not have adjust too much. Maybe try it with a scan gauge on there and flip them back on if it gets bad.