Occasionally switching off injectors on one bank of cylinders...
 

Hi there.

I have a 3 litre Alfa Romeo GTV V6 as a second car. Its fuel economy is very poor and I'd like to use it more (instead of my diesel daily runner).

I was wondering if it was possible to save fuel (when performance wasn't needed) by cutting out the power to some (half?) of the fuel injectors.

If I had a couple of toggle switches on my dashboard which allowed me to cut the circuit powering the injectors on each bank of cylinders, I could run the front bank, the rear bank or both.

That would allow me to run my 3 litre car in 1.5 litre or 3 litre "mode".

The only possible problem that I suspect is possible overheating or wear in the bank which is "off". I'm not sure if the intake gasses could also act as a lubricant for the piston or rings.

I'm sure this has been discussed before but I would love to know peoples opinions.

Thanks

James

try running the engine with three cylinders and see how it goes. your idea isn't too far fetched but I think a better question you should ask yourself is, why does your vehicle get such poor mileage in the first place?

Yes, I'll give it a go and see. I just wanted to see if there where any major reasons why I shouldn't - I dont want to wreck my engine.

The milage I get is typical for the car. There's nothing wrong with it. I just can't afford the fuel to use it as a daily commuter - especially with the silly prices for petrol here in the UK - about ?6GBP a gallon - madness.

One thing to watch for... If the computer goes into limp home mode when it doesn't get a signal from the disabled injectors. You may get even worse mileage.

Yes, I heard about that from a friend. However, if I could switch the injectors circuitry onto a dummy load (with the same resistance as the injectors) then the ECU wouldn't "know" the injectors were off. Wouldn't be that hard to rig up..

James

If there is an oxygen sensor downstream from the bank that is shut off, the ECU it will see the extra oxygen, assume it is running lean and cause the working injectors to inject more fuel.

Several years ago, I disabled one injector on my 4 cylinder Acura and saw no mpg benefit (and the engine ran really rough at low rpms).

Now thats a very good point Erik. Thanks.

Oh well, it was a nice idea while it lasted.

James

This is the key factor. Also if you do the math its doesn't save you that much based on the engines needed output to propel the vehicle.

The major gains of shutting off cylinders don't come until you can shut off more than just the fuel injection. You also need to be able to shut off the valves. That's how modern displacement-on-demand systems are able to increase efficiency.

If you really want to get better fuel economy from your Alfa, there may be other options. How is it geared? An Alfa owner on another forum, with a 1974 GTV, has extremely short gears...

Honda has a V6 where 3 cylinders are shut off (VCM: Variable Cylinder management). But it's more complicated than just stop the injection. It's a combination where the V-tec system closes the valves of the shut down cylinders.
As said here before, because of the lambdasensor the ECU would definitely notice the fuel cut off. But maybe you have two lambdasensors? For each cylinderbank? But even than, your ECU will only generate troublecodes because it's unable to compensate.