GM 4.2 liter V-6 Deactivation - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 07-26-2008, 02:17 PM   #1
Registered Member
 
Join Date: May 2008
Posts: 14
Country: United States
Question GM 4.2 liter V-6 Deactivation

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.
__________________

jwa4871 is offline   Reply With Quote
Old 07-26-2008, 02:48 PM   #2
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to 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
__________________

__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 07-26-2008, 07:21 PM   #3
Registered Member
 
kamesama980's Avatar
 
Join Date: Nov 2007
Posts: 742
Country: United States
Location: Columbus, IN, USA
Send a message via AIM to kamesama980 Send a message via Yahoo to 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.
__________________
-Russell
1991 Toyota Pickup 22R-E 2.4 I4/5 speed
1990 Toyota Cressida 7M-GE 3.0 I6/5-speed manual
mechanic, carpenter, stagehand, rigger, and know-it-all smartass
"You don't get to judge me for how I fix what you break"
kamesama980 is offline   Reply With Quote
Old 07-26-2008, 07:44 PM   #4
Site Team / Moderator
 
Jay2TheRescue's Avatar
 
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,657
Country: United States
Location: Northern Virginia
Quote:
Originally Posted by kamesama980 View Post
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.
__________________






Jay2TheRescue is offline   Reply With Quote
Old 07-26-2008, 09:48 PM   #5
Registered Member
 
Join Date: May 2008
Posts: 14
Country: United States
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 is offline   Reply With Quote
Old 07-26-2008, 10:11 PM   #6
Registered Member
 
Join Date: May 2008
Posts: 14
Country: United States
OK so it's a 4.3 liter, just a liter mistake.
jwa4871 is offline   Reply With Quote
Old 07-28-2008, 09:07 AM   #7
Registered Member
 
Join Date: May 2008
Posts: 14
Country: United States
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 ?
jwa4871 is offline   Reply With Quote
Old 07-28-2008, 09:21 AM   #8
Site Team / Moderator
 
Jay2TheRescue's Avatar
 
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,657
Country: United States
Location: Northern Virginia
Quote:
Originally Posted by jwa4871 View Post
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.
__________________






Jay2TheRescue is offline   Reply With Quote
Old 07-28-2008, 11:24 AM   #9
Registered Member
 
Join Date: May 2008
Posts: 14
Country: United States
Makes sense, is installation a problem?
jwa4871 is offline   Reply With Quote
Old 07-28-2008, 11:37 AM   #10
Site Team / Moderator
 
Jay2TheRescue's Avatar
 
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,657
Country: United States
Location: Northern Virginia
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.
__________________

__________________






Jay2TheRescue is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What is the FE sweet spot for... bowtieguy Transmissions and Running Gear 14 09-05-2008 07:18 AM
1990 ford tempo gl problems (need advice asap) od_satan General Maintenance and Repair 4 03-19-2008 07:23 AM
I got an EV! lovemysan Electric and Solar powered 14 11-17-2007 08:55 PM
84 Grand Waggoneer to 98 S-10.... dimmak Introduce Yourself - New member Welcome 4 05-20-2007 01:23 PM
How far do you drive daily? OdieTurbo General Fuel Topics 56 03-31-2007 02:49 AM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 05:07 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.