How to improve DFCO and P&G

[goofy1]

I've been trying to get my car to DFCO better. For example: at 55MPH I EOC, the scan gauge shows (in MPG) 100, 250, 9999. But once it eachs 9999 it only last (i have timed it) 5 - 10 seconds and it goes back to 214MPG every single time. The Vibe we have will show 9999 for much longer and will EOC great. When we P&G in the Vibe, the speed decreases slowly. By contrast the Prizm, the speed decreases faster. I would figure the Prizm would do better at P&G then the Vibe because its way lighter. Any thoughts on this?

[theholycow]

P&G and DFCO both depend heavily on inertia. The heavier car has more inertia.

DFCO also depends heavily on programming; different programming will be more or less aggressive with it, use different criteria for allowing or canceling it, etc.

Additionally, DFCO depends heavily on gearing; didn't you say your Prizm is a 3 speed automatic?

You could possibly add in a switch that disables the injectors, for driver-forced fuel cutoff. I'm not sure how much you might be able to gain by doing it. Another option would be a custom tune, which will only pay for itself if there is cheap hardware and free software for DIY tuning.

Edit: One more thing: Scangauge behavior differs from vehicle to vehicle as not every computer communicates with the SG the same way. You may be seeing measurement differences as much as behavior differences. You could use a meter directly on a fuel injector to get a better feel for what's going on.

[goofy1]

no, the Prizm is not a 3 speed, it's a 4 speed. I didn't want a 3 speed because it's too hard to get good MPG.

[trollbait]

If you are engine off coasting, you won't see the vehicle's DFCO behavior.

My scangauge won't show DFCO in the mpg display. I have to use loop(LP) to do it. If the engine is warm, I'm coasting in gear, and loop is open, I assume it's DFCOing. Then again, my scangauge is an older version.

Unless the engine has advanced valve control and shuts them during DFCO (likely not on older cars) engine braking will increase while under DFCO. Unless you are coming to a stop, neutral coasting might be better than using DFCO.

[theholycow]

Good point. Even if your SG does seem to display 9999 obediently, it always seems to be more responsive to open loop.

Also agreed on neutral vs. DFCO...I've mentioned my experience with Pulse&DFCO in a couple other threads recently. At least one person seems to have success with it though.

[goofy1]

I never EOC. It's too hard on the automatic transmission. The engine is the first year for Toyota's VVT-i in the corolla(USA) But it's the same engine in the Vibe (though the Vibe has 6 more hp) I get worse MPG coasting in neutral.