: Turning off Injectors = Save fuel?

08-29-07, 02:43 AM
Ok so I've been reading about the northstar PCM and the override fuction (pre 96). In the override function you can disable each individual fuel injectors. I'm woundering, If i disable 2 or 4 of them (matching the firing order so there aren't two in a row off, i.e. every other one) would I save fuel on road trips? This probably wouldn't be a good idea in town driving. Would there be able harm is disabling the injectors and driving it?

08-29-07, 07:40 AM
With 2 or 4 cylinders disabled fuel-wise, but still functioning mechanically, the load generated would require the other cylinders to "pick up the load". You would probably lose gas mileage. I think the cylinder disable was (is ?) a loss of coolant "limp home" strategy, gas mileage be damned.

08-29-07, 08:33 AM
You would probably lose gas mileage.


The DoD systems from GM disable cylinders by turning off the valves. The air inside those cylinders then acts like a spring as it gets compressed and expanded. If you don't turn off the valves, you still have significant pumping losses due to the airflow through those cylinders. So you'd lose mileage.

08-29-07, 09:08 AM
eldorado1 You missed the biggest issue. All the O2 going past the O2 sensor. This would cause the PCM to think it was What?
The PCM would the adjust the air fuel mixture and cause it to be what?

08-29-07, 09:23 AM
Disconnect the o2 sensors and lock the fuel trims, and it will still run with worse gas mileage.

08-29-07, 10:41 AM
I think what Gizmo is talking about is the cylinder balance test and only disables the injectors while holding a button. I don't think it can be selectively (permanently) disabled. That said, I agree, I think it would be self defeating.

08-29-07, 01:14 PM
If it was really as easy as dropping injectors at cruise RPM, everyone would do it. It's really much more complex than that, which is what eldorado1 was saying.

08-29-07, 02:37 PM
Well thanks for the feedback guys.. I was just curious because I've heard of these newer vehicals that have the ability to turn off cylinders to save gas... Guess they use a much more complex system. Thanks