Eliminate Some Cylinders?

My 1999 Nissan Quest uses too much gas. I think it’s partly because the slightest push on the gas pedal causes it to take off like a bat out of hell. The throtle doesn’t stick anymore since I fixed it. So I was thinking about disconnecting two of the injector wires and pulling the plugs to convert it to a 4 cylinder in order to reduce power and get better mileage. I’m sure that will throw a code, but I don’t care about that. Will it work, and will it damage anything? If the open cylinders make too much noise, I can plumb them to some kind of small muffler. Or, is there any other way to limit the throttle so it can’t be opened so much or so quickly?

No! This can’t be done.

If you do this, those cylinders that aren’t firing will pump air into the catalytic converter(s). This will cause the cat(s) to overheat and the cat(s) will have a meltdown.


Sure, you can do that, but it’ll run like a motor with 2 cylinders missing. That is to say, quite poorly.

And you are still pumping those unused pistons and connecting rods up and down which is where most of the mileage is lost. Pumping losses.

If you want a 4 cylinder vehicle, buy one. Don’t butcher what you have.

So should I even ask what your fuel mileage is and how it’s being figured?.

If it really has a fuel mileage problem then how about fixing it instead of jumping off the deep end. Attempt this ridiculous stunt and your mileage will drop even more.

I’m sure that will throw a code, but I don’t care about that.

You may very well care if your state has emissions tests. For some states, emissions testing no longer means inserting a probe in the tailpipe. It’s simply a matter of checking for any stored fault codes.

It would run rough and it would use MORE fuel, not less.

If you can’t control it so you get a slow smooth acceleration, you or the accelerator needs to be adjusted.

Not only is it a bad idea, but my head almost exploded reading this idea. It isn’t your Nissan Quest that uses too much gas, it is you that uses too much gas. Think about finding ways to drive less or lighten your load. Do you use the rear seats? Are they removable? The add a lot of weight and removing rear seats that you don’t use could improve fuel economy. Do you make two trips when you could have made one if you had planned better? Do you drive the car every day of the week? Why not pick a weekend day that you will do no driving unless it is absolutely necessary? Have you looked into car pooling? Do you own a bicycle with a basket that could be used for running to the store for milk and bread instead of driving? There are a lot of things you can do to save fuel that don’t involve butchering your engine. Get creative but keep it simple.

Thanks for the alternative fuel saving ideas, but I do all those things anyway. I even have a 68 MPG scooter we use as much as we can. You and most of the others have missed my point. There is nothing wrong with the way I drive nor is there anything wrong with the van. It gets about 18 MPG when my wife drives it 5 miles to her school and back. Maybe 24 on the highway. The newer models get much better mileage and some engines DO shut down a couple of cylinders to conserve fuel. How do they do that? There IS a correct way to engineer a cylinder shut off. I’m not trading my $5000 van for another $30,000 vehicle just to get 10 more MPG. You need to stop yelling at me about the way I drive, put your head back together and let someone who knows about engines advise me.

So, how do they do it on other cars?

The engines that are able to shut down cylinders not only turn off the injectors and spark to those cylinders. but they also disable the valves for those cylinders so they don’t open and close. If this wasn’t done, the cat would be destroyed.


Who is yelling? I know something about engines and I can tell you that those engines that shut down cylinders that aren’t needed are designed to do so. Yours isn’t designed to do so and there is nothing you can do to make it work. The first flaw that came to my mind is that removing the spark plugs will allow contaminants to get into the engine and oil might leak out.

I may not be a mechanic, but I have educated myself about how engines work as an enthusiast. Also, I don’t think my posts here prevent anyone who “knows about engines” from advising you. It isn’t like my contribution to the conversation gets in someone else’s way.

I know far too many people who have chosen lifestyles that are not sustainable. They blame high taxes, the high cost of fuel, and even their vehicles for their problems. So if the cost of fuel is causing that big of a crisis, a change of lifestyle might be the best solution. You may not like hearing it, but I will say it anyway.

My brother has an old Lincoln that seemingly has a cylinder elimination set-up. It runs on all the cyliners some of the time. It runs on some of the cylinders all the time. However, it won’t run on all its cylinders all the time. Running on fewer cylinders doesn’t seem to help the gas mileage.

It is a myth that fewer cylinders yield better gasoline mileage. In 1950, one of the more economical cars was a Cadillac with an OHV V-8 engine. On the other hand, the 1950 Chevrolet with the PowerGlide automatic transmission and a 6 cylinder engine didn’t get very good mileage and under most circumstances, not as good as the Cadillac.

The late Les Viland who won many Mobilgas Economy runs wrote an article about getting high mileage. He said to drive as if there was an egg on the accelerator pedal. You didn’t want to push the pedal hard enough to break the egg. He also suggested driving with light shoes rather than heavy boots. In most cases, the engine set-up that gives the best performance gives the best mileage because you are getting more out of that gallon of gasoline.

Wouldn’t this also ‘unbalance’ the engine in some way making it run very rough?

One way is to use a cam shaft that slides from side to side. The cam shaft can shift to a position where there are fewer lobes pushing the rods that open and close the valves. It also has a crank shaft that can disengage some of the cylinders. It has a mechanism that releases a part of the crank shaft from the part that is still turning. According to http://www.freepatentsonline.com/6273840.html “Injection valves are controlled by an engine timing system as a function of vehicle operating conditions. The shutting-down of cylinders is carried out sequentially according to a defined program.”

SolarMark, the people who have been advising you are experts in the field. You would be hard pressed to find people more knowledgeable about engines than some of these guys. Listen to them, they know what they’re talking about.

From your description, you have difficulty feathering (getting smooth and gradual responses) with your throttle. The throttle position sensor (tps) is probably non-linear; that is, it may be worn and doesn’t send a smooth , progressive signal to the engine computer. When the engine computer gets the (non-linear) signal from the tps, it sends control signals to the iac (idle air control) valve, the fuel injectors, and spark control. As a result, you get a sudden rush of engine power (acceleration). Check the tps with a digital voltmeter. Check volts and ohms (with ignition key off). As you slowly, smoothly move the throttle, the volts and ohms should increase, or decrease, smoothly. If not, the tps is defective.

It sounds like your fuel mileage falls into the “normal” category.

Eliminating cylinders, whether by choice as you would like to do, or by the original design, does not automatically mean better fuel economy.
My Lincoln Mark with the 4.6 V-8 gets 27 MPG on the road and has even hit 30 a few times. With the A/C running and at a 70 MPH cruise.
Engine design and torque play a big role in this.

Very helpful. Thank you, I’ll check that.

Thank you. That’s what I was looking for.