Dynamic Cylinder Deactivation

[christofoo]

Originally Posted by razor02097

I don't think so. If it were emissions then DFCO wouldn't have been used. There is no way to accurately measure the efficiency of the engine when pumping pure air through the exhaust in an engine running state. That is why variable displacement engines physically hold the exhaust cycle so when the cylinder is active again it can expel the exhaust and intake air and fuel.

Think about it the O2 sensor senses O2. You pump ambient air past it and it will swing crazy lean. The ECU responds by adding fuel to that bank.

It is the same problem in both regards with respect to lean-burn. EDIT...

EDIT: the fuel mixture issue is solved with a wideband O2 sensor.

EDIT EDIT: sorry, I'm not so certain about emissions. Lean-burn doesn't work with a 3-way cat because of the exhaust chemical composition - my bad. Low cat temp during DCD seems like a reasonable presumption to me. Maybe this is an effect I could quantify on paper if I thought about it. My understanding is that DFCO is intended to protect the cat from unburnt fuel under deceleration. The fact that it is done, and done at a low air mass flow rate I might add, may not be an indicator that DFCO is good for emissions. Perhaps it's a compromise in that regard. Tolerate cat cool-down instead of destroying it permanently. EDIT EDIT EDIT: I can find opinions, but haven't found anything definitive on the design intent of DFCO. Can you?

[christofoo]

Originally Posted by Frank Lee

^Nope.

Well this is embarrassing. I skimmed that doc too quickly. It is not a similar mod. Not similar enough. Thank you Frank.

[Frank Lee]

Additionally, I don't think providing separate exhaust pipes and O2 sensors for active and deactivatable cylinders is any sort of technical impediment.

[t vago]

Originally Posted by Frank Lee

Additionally, I don't think providing separate exhaust pipes and O2 sensors for active and deactivatable cylinders is any sort of technical impediment.

Yes, but why would you do that? That's just adding needless complexity in an alright-tight engine bay.

[Frank Lee]

I wouldn't do it because merely killing injectors is pointless, but some are arguing that the only reason killing injectors doesn't work is because of the effect on the O2 sensors. If that was the only hang-up then a dual exhaust could certainly be provided.

[t vago]

Originally Posted by Frank Lee

I wouldn't do it because merely killing injectors is pointless, but some are arguing that the only reason killing injectors doesn't work is because of the effect on the O2 sensors. If that was the only hang-up then a dual exhaust could certainly be provided.

Good point. For 4 bangers, it wouldn't be that big a deal to set up the exhaust plumbing as you've described, now that I think about it.

I had V-engines in mind, though. However, some V-engines could certainly be configured such that an entire bank could be shut off for cylinder deactivation. Certainly, the V6 engine in my Magnum could be fitted, as it has a firing pattern of 1-2-3-4-5-6. Shut off the right bank, for instance, and the firing pattern would become 1-x-3-x-5-x, and I'd end up with a fairly evenly running I3. There is no need to change the exhaust plumbing, and the O2 sensors in the shut-off bank could simply be ignored.

Now, most production V8 engines, on the other hand... The V8 in my Dakota has a firing pattern of 1-8-4-3-6-5-7-2. Shut off the right bank, and I'd end up with 1-x-x-3-x-5-7-x. That's not terribly well balanced.

[razor02097]

Originally Posted by Frank Lee

I wouldn't do it because merely killing injectors is pointless, but some are arguing that the only reason killing injectors doesn't work is because of the effect on the O2 sensors. If that was the only hang-up then a dual exhaust could certainly be provided.

Even a dual exhaust isn't going to solve the issue. The issue is ambient air hitting the O2 will cause the O2 sensor to false lean. With a dual exhaust you will still have sensors on each bank. If you are putting a split manifold on 4 cylinder and only putting an O2 on one pipe the ECU won't be able to monitor the burn cycle on the other cylinders.

[serialk11r]

Originally Posted by razor02097

Even a dual exhaust isn't going to solve the issue. The issue is ambient air hitting the O2 will cause the O2 sensor to false lean. With a dual exhaust you will still have sensors on each bank. If you are putting a split manifold on 4 cylinder and only putting an O2 on one pipe the ECU won't be able to monitor the burn cycle on the other cylinders.

Uh, that's why you have an O2 sensor for every bank, like my car and 10 million Corollas and Celicas out there? (cylinders 1,3 and 2,4 are paired, each have their own O2 sensor)

[razor02097]

Originally Posted by serialk11r

Uh, that's why you have an O2 sensor for every bank, like my car and 10 million Corollas and Celicas out there? (cylinders 1,3 and 2,4 are paired, each have their own O2 sensor)

Please read it again. You are telling me nothing new.

Originally Posted by razor02097

Even a dual exhaust isn't going to solve the issue. The issue is ambient air hitting the O2 will cause the O2 sensor to false lean. With a dual exhaust you will still have sensors on each bank. If you are putting a split manifold on 4 cylinder and only putting an O2 on one pipe the ECU won't be able to monitor the burn cycle on the other cylinders.

You misunderstood my post. I am saying if you were to get rid of a sensor on one of the banks the ECU couldn't monitor that bank.

[Frank Lee]

The O2 sensor for the deactivatable cylinders could be deactivated in unison.