GM 4.2 liter V-6 Deactivation

[jwa4871]

I want to deactivate one bank of three cylinders to see if, or how much, it will improve my mileage. Pulling three spark plug leads proved the engine will start and run smoothly, giving me about as much performance as my old '46 Chevrolet did. I'd be happy with that.

I plan to back off the lifters on one bank so the pistons are just bouncing on air. Obviously some friction loss there.

I plan to disconnect the fuel injectors on the one bank.

I am concerned that the Oxygen sensor on the deactivated bank will remain cold, and therefore tell the computer to keep the mixture rich. I need some advice there. That would also result in not being able to pass a smog test.

I can't imagine no one has ever tried this before, so there must be some good advice out there.

[theholycow]

There's a few threads about it. Here's one, for example:
http://www.gassavers.org/showthread.php?t=7132

Since vBulletin's search function stinks, it's easier just to use google to search the forum. Here's the search I used to find that thread:
http://www.google.com/search?q=site:...rs.org+diy+dod

[kamesama980]

few things about it.
1. what make model and year is your car? the only 4.2 6 cylinder I know of from GM is the L6 in the trailblazers. I take it yours is a much older car?

2. search. several people have tried it. both the attempts I saw failed miserably or stopped before breaking things.

[Jay2TheRescue]

Originally Posted by kamesama980

few things about it.
1. what make model and year is your car? the only 4.2 6 cylinder I know of from GM is the L6 in the trailblazers. I take it yours is a much older car?

2. search. several people have tried it. both the attempts I saw failed miserably or stopped before breaking things.

I've read about people doing that with Chrysler V-8's in the 70's. I imagine if you tired to do it now it would throw a computer code. You can buy a car that will do it on demand. The older Cadillac Northstar engines did it, and many current GM models will do it as well. GM calls it "Active Fuel Management". When at highway speed and low load the computer will deactivate half of the cylinders.

[jwa4871]

JWA4871
My vehicle is a 1998 GMC Sonoma pickup with a 4.2 liter V-6

What's to break ? It starts and rums smoothly on 3 when I pull the plug wires on one bank.

[jwa4871]

OK so it's a 4.3 liter, just a liter mistake.

[jwa4871]

OK, still concerned about the O2 sensor. If I kill one bank, certainly the sensor will be cold (open loop) I'm wondering if I only deactivate two cylinders on that bank, leaving the one closest to the O2 sensor active, would that provide enough heat to put the sensor in closed loop mode?

I expect the engine would not run as smooth as it did running on three, and maybe some other combination of four would be better.

Any comments ?

[Jay2TheRescue]

Originally Posted by jwa4871

OK, still concerned about the O2 sensor. If I kill one bank, certainly the sensor will be cold (open loop) I'm wondering if I only deactivate two cylinders on that bank, leaving the one closest to the O2 sensor active, would that provide enough heat to put the sensor in closed loop mode?

I expect the engine would not run as smooth as it did running on three, and maybe some other combination of four would be better.

Any comments ?

Why not relocate the unused O2 sensor to the side that is being used, so it gives the computer the numbers its looking for, and not throw a code.

[jwa4871]

Makes sense, is installation a problem?

[Jay2TheRescue]

I would imagine all you would have to do is extend the wires to the other side, and drill & tap a hole on the other side to mount it in the exhaust.