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Fuel Economy Discuss how to achieve better fuel economy.

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Shut off Fuel Injectors Manually

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Old 08-12-2008, 11:07 AM
visionseeming visionseeming is offline
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Shut off Fuel Injectors Manually

Well, my dad, who recently got into saving gas, after reading about multi-displacement engines, suggested that if we remove the power wire to one of the fuel injectors on his V6 Nissan Quest, that it should use less gas as it is now only effectively a 2.5 liter engine, and thus can save gas, while cruising at least.

Obviously, I am not sure if this works, we do not have a SG or SGII and have no way of seeing if less gas is actually used or if mileage goes up, on a short run. We tried this yesterday during a short drive, and it was a little rough in gear while stopped, but above about 1200 rpm or so, the engine didn't seem to run roughly. It also idled normally (in park and neutral).

Has anyone experimented with this before? Do you think it might damage the engine in some way?
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Old 08-12-2008, 11:19 AM
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Re: Shut off Fuel Injectors Manually

This is a difficult concept, however if you think about it, the engine will have the lag of the v 6 as it is still compressing the air, but not producing the power for any additional turning. Granted as the air becomes uncompressed it does release SOME energy as in a spring loaded mechanism.

This idea might fool the ecu and throw a cel code on most cars. It will still be firing the spark plug which you might hear through the exhaust and depending on the car it may work but not so well on others.

Because a V6 is heavier, you'll have a smaller engine carrying a larger load and messing with the injectors that way may cause the timing on your engine to be off which explains your rough idling. I wouldn't recommend it as it may cause some issues.

If you can selectively deactivate 2 of the cylinders while in motion, there might be some benefit there as far as cruising, it also might run rough for a while until your ecu learns or throws a cel code.

There is a lot of research that went into cylinder deactivation tech and the injectors have to be carefully selected. Make sure if you are going to try it you know the firing order and which one or two would be best to deactivate to prevent your engine running rough. Like I said, you will probably get a cel code.
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Old 08-12-2008, 11:20 AM
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Re: Shut off Fuel Injectors Manually

Btw, I have toyed with the idea, but dismissed it. Not impossible as I'm sure it'll work on some cars, not all.
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Old 08-12-2008, 11:25 AM
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Re: Shut off Fuel Injectors Manually

Interesting. So you would be deactivating that injector by removing its power, right? The only problem is that the timing will be off balance, because it is currently sychronized to smoothly crank based upon 6 cylinders. Decades ago, when I tinkered with my car, I noticed that if not all cylinders are firing, the idle is very rough and off balance, so that 3 out of 4 clyinders firing seemed to cut the power to 50% instead of 75%. I think in modern "cylinder deactivation" , they avoid this imbalance by deactivating muliple cylinders in different parts of the cycle, as well as, adjust the timing of the sparks to maximize efficiency. In short, I don't think this idea will improve FE, but might be worth a try.
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Old 08-12-2008, 07:22 PM
LinD LinD is offline
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Re: Shut off Fuel Injectors Manually

One of the problems I foresee with simply disconnecting a fuel injector is that the O2 sensor will see extra O2 in the exhaust and the ECU will enrich the mixture to compensate. This will cause the remaining cylinders to be too rich, negating any gains sought. Also, that piston will be a big drag to the engine, with pumping losses and frictional losses.
To do it right, I believe you would have to either keep both valves shut or keep the exhaust valve shut and the intake open continuously. First, this will keep air (and O2) from being pumped into the exhaust and messing up the mixture control loop, second, it will basically eliminate the pumping loss.

Thinking this over, I know that my '01 Audi ECU reports individual cylinder misfires, so it wouldn't be very happy, but my '99 Civic probably wouldn't notice!

-Lin
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Old 08-12-2008, 08:02 PM
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Re: Shut off Fuel Injectors Manually

most newer vehicles will set DTCs for misfires, P0300, and you will likely also get a P020X for the injector you disable. The multiple displacement engines also keep the valves closed on the deactivated cylinders.

I rigged up an injector kill switch on my Saturn that cuts power to all 4 injectors (by wiring a fused switch where the injector fuse was) to stall the engine for long coasts so that I dont have to power the PCM down by shutting the engine off with the ignition switch.
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Old 08-12-2008, 09:13 PM
phoebeisis phoebeisis is offline
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Re: Shut off Fuel Injectors Manually

Interesting, but it will run very rough.
If you do it ,I would be tempted to pull the spark plug- might slightly decrease pumping loses. Unfortunately, you would be pulling in unfiltered air filled with road grit stirred up by the tires.More trouble than its worth to try to fit a filter on the plug hole.

It will really idle rough-pull one of the plug wires and see how it runs-?

Luck,
Charlie
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