Thread: Running 3 Cylinders

The valves will still open and close as they should so there will be air movement. The piston will compress air as it normally would and that energy will be mostly returned on the piston's return trip back down (it's like jumping on one of those big air-filled balls). And you don't want the cylinders to cool because it could create problems such as uneven wear, which is why I might want to alternate which bank is being used while the engine is running to make sure temps stay close and wear is balanced.

The only issue I see from what I've read from the disadvantages of displacement on demand is the blow by created from all the oil sitting there when the piston refires.

Other than that...I don't see an issue with it. I'd actually like to see how you figure it out Colton. Get at it boss.

Doesn't GM already have some bit of tech that alternates firing groups of cylinders? I am thinking of the Northstar and the 3400 in the Buick Rendezvous. When these cars overheated a engine protection mode would activate and fire some of the cylinders.

Originally Posted by bluegtp91

The only issue I see from what I've read from the disadvantages of displacement on demand is the blow by created from all the oil sitting there when the piston refires.

Other than that...I don't see an issue with it. I'd actually like to see how you figure it out Colton. Get at it boss.

Oil causes blow-by? Elaborate.

Originally Posted by EJOUIE

Doesn't GM already have some bit of tech that alternates firing groups of cylinders? I am thinking of the Northstar and the 3400 in the Buick Rendezvous. When these cars overheated a engine protection mode would activate and fire some of the cylinders.

I was also reading about this, however it wasn't meant to be a fuel-saving technology so much as it was an engine-saving technology.


Now, I haz new idea in case the original doesn't work out. Probably much simpler in terms of concept and execution, and would require less work (probably):

Run 2 PCMs simultaneously, with only one controlling the vehicle at a time. Continuously feed both PCMs input data, but only accept output data from one at a time (this would keep them happy with all the sensor input. This combined with a small circuit designed to toggle each bank of cylinders (for temperature and wear consistency; based off an injector kill-switch principle) at a given interval, would allow for an eco tune (adjust spark, safely leaning out fueling, change throttle ramping for DBW, etc) and a performance tune to live within the same vehicle simultaneously. The vehicle would always start with the performance tune, and an activation control circuit would be implemented to make sure the eco mode couldn't be activated until the vehicle was effectively warmed up.

The dual PCM idea does seem less likely to be able to work, however it's still a valid option at this point. Questions? Comments? Concerns?

One more thing -- how does the DIC compute fuel economy?

So you would have one PCM function normally and the other would run the engine on 3 cylinders? Performance and economy?

Originally Posted by EJOUIE

So you would have one PCM function normally and the other would run the engine on 3 cylinders? Performance and economy?

Correct. The point of this is to have the best of both worlds, or at least get somewhat close.

I do think that there would be a problem with both PCMs being on at the same time as I am unsure of how to have one only watch and the other work. I also don't see the need to have both on simultaneously. A simple switch from one to the other may work well. Shut one off and turn on the other while driving. Probably will need to do some programing magic so that the PCM doesn't freak out with the engine already running.

Originally Posted by EJOUIE

I do think that there would be a problem with both PCMs being on at the same time as I am unsure of how to have one only watch and the other work. I also don't see the need to have both on simultaneously. A simple switch from one to the other may work well. Shut one off and turn on the other while driving. Probably will need to do some programing magic so that the PCM doesn't freak out with the engine already running.

It's my understanding that the outputs from the PCM never get checked to make sure their signals are received by whatever needs them, which means as long as the PCM is getting a good signal from all the sensors and the like (which it will, because the engine and everything else is running fine), it thinks that everything is ok and all signals are being received (whether they be from PCM 1 or 2). The problem with turning on a PCM during engine operation is that it may attempt a startup sequence that kills the engine or some other necessary functions. I believe it would be much easier to turn them both on at the same time so this is all out of the way and they're both in their normal operating loop.

Another thing I have seen is the ability to have a dual flash PCM where there are two EEPROMS that can be manually switched between, however this needs to be done while the vehicle is off so there goes that idea.

Would the performance PCM flip out when it sees the engine running on 3 cylinders? What kind of difference would there be between the output signals at the point of switching between the two?
I'm currently trying to learn about tuning so this PCM stuff is making more sense.

Considering some guy got a DeLorean to run on both a B18 AND SBC at the same time, this can be done.

Would the PCM ever know if the engine was running on 3 cylinders at all? Because my idea for that is just cutting off the signal to the injectors, which again is an output from the PCM, which doesn't receive input confirming the signal was received by the injector(s) (to my understanding). Someone with more PCM knowledge can chime in at any time. I also am trying to learn more about these things, because as stated previously in this thread I was also planning on utilizing an open source PCM option, so anything and everything is possible when it comes to programming.

Originally Posted by Confusingboat

Another thing I have seen is the ability to have a dual flash PCM where there are two EEPROMS that can be manually switched between, however this needs to be done while the vehicle is off so there goes that idea.

How does performance shift work? Would that be able to be reprogrammed to make the change that you looking for?