Redneck DoD

[mpyusko]

So I'm thinking about going on a road trip, cross-country, and I had this thought about wiring a couple switches. One grounds out Injectors 1, 4, 6, and 7. The other grounds out 8, 3, 5, and 2. (Firing order is 18436572). The goal is to increase my gas mileage on the highway. By having 2, I can switch between them to ensure more even wear.

The thought came about since my #3 injector has been consistently misfiring and I've increased my MPG from 11.5 to 12.7 average, and 16+ Highway (from 13.5) without any noticeable loss of highway performance (takeoff is a bit slower though.) I was also considering GMs Displacement on Demand for exactly this purpose. But an actual DoD setup rotates through the cylinders to more accurately wear evenly and it (of course) enables and disables itself automatically.

So besides my computer throwing codes for constant misfires, can anyone see any reason not to do this for those many hours cruising at highway speeds?

It's a 96 Vortex 7400 (454). Just my truck, kids and luggage. Not towing. Nothing on the rack. Constructive responses appreciated. Thanks.

 

[Komet]

Ah yes, the widely adopted and much celebrated Displacement on Demand. Unless you've got a way to stop the valves from opening, this is a bad idea. You should replace your injectors with a flow matched set of new ones before the trip.

 

[GoToGuy]

And unicorns are real.

 

[L31MaxExpress]

DOD or whatever they want to call it this week disables the valves, using the air in the cylinders to act as a spring. Replace your injectors and have a safe trip.

The newer systems can run on 1 cylinder, but the older DOD setup deactivated the same 4 cylinders every time.

 

[mpyusko]

Ah yes, the widely adopted and much celebrated Displacement on Demand. Unless you've got a way to stop the valves from opening, this is a bad idea. You should replace your injectors with a flow matched set of new ones before the trip.

Not so sure why keeping the valves closed is so important. It is not sucking mixture in, just atmosphere. Then it's compressing and sparking like normal, and blowing out the exhaust. With the usual resistance on all the components, I would expect the worst scenario is a drop in the exhaust temps. (Unlike that time I had to drive the 2.2L in our cavalier, for a week with only 3 plugs in it because one popped out. Had a loose wrist-pin for the rest of its life... over 100,000 more miles, and then some... We got rid of the car with over 250k on the engine). So anyway.... yeah replacing the injectors is on my list since I have over 300k on the original set.

Thanks.

 

[mpyusko]

And unicorns are real.

The national animal of Scotland so..... who's gonna break it to the Scott's?

 

[95burban]

I got rid of DOD asap, not sure why you would want to make your own. A good properly maintained engine will gain you the MPG you’re looking for. And a 3/4 or 1ton truck needs all the power it can get.

But, I will give you credit for thinking outside the box.

 

[0xDEADBEEF]

Not so sure why keeping the valves closed is so important. It is not sucking mixture in, just atmosphere. Then it's compressing and sparking like normal, and blowing out the exhaust. With the usual resistance on all the components, I would expect the worst scenario is a drop in the exhaust temps. (Unlike that time I had to drive the 2.2L in our cavalier, for a week with only 3 plugs in it because one popped out. Had a loose wrist-pin for the rest of its life... over 100,000 more miles, and then some... We got rid of the car with over 250k on the engine). So anyway.... yeah replacing the injectors is on my list since I have over 300k on the original set.

Thanks.

It's pumping air into the exhaust that the O2 sensors are going to read and the PCM is going to dump more fuel in to compensate.

 

[Supercharged111]

Not so sure why keeping the valves closed is so important. It is not sucking mixture in, just atmosphere. Then it's compressing and sparking like normal, and blowing out the exhaust. With the usual resistance on all the components, I would expect the worst scenario is a drop in the exhaust temps. (Unlike that time I had to drive the 2.2L in our cavalier, for a week with only 3 plugs in it because one popped out. Had a loose wrist-pin for the rest of its life... over 100,000 more miles, and then some... We got rid of the car with over 250k on the engine). So anyway.... yeah replacing the injectors is on my list since I have over 300k on the original set.

Thanks.

Keeping the valves closed reduces pumping losses. Even when it's functional from GM it doesn't make a hill of beans worth of difference.

 

[0xDEADBEEF]

Keeping the valves closed reduces pumping losses. Even when it's functional from GM it doesn't make a hill of beans worth of difference.

I never had a GenIV with DoD, but the GenV DoD does work (assuming the instant MPG display isn't programmed to lie). It's a lot more effective in my Corvette than it is in the Yukon though. The C8 can stay in V4 for hours, but the Yukon being a big heavy brick never stays in for long.