MDS is not an option on a any inline engine that I know of. :shrug:

 

My Saturn would cut fuel when in gear and decelerating as long as you were above a specific speed.


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My SC1 2001 Saturn with a 1.9L inline 4 that is.


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hmmm, did not know that. I doubt if it can be tuned into our exisiting PCM. My guess there are a ton of mods that would need to be done to make it happen on a 355.

 

There is a section in our PCM's that relate to DFCO - Deceleration Fuel Cut Off. Your truck does have it enabled, it just has such a small window that you dont notice it. from all of the stock 355 tunes Ive looked at the DFCO only applies during a coast down from 1700rpm to about 1400rpm. silly I know, but its there! It can be changed with HPtuners as you see in the next post, but I wouldnt mess with it.

 

Wow! Thanks for the info!!! If it has ever happened in my 05 I have never noticed it by feel or by watching my scan gauge.


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This is a stock 2007 tune file:

 

SO it's essentially engine braking? If so, I know my truck definitely engine brakes, but it has to be gaining speed with your foot off the throttle before it kicks in.

Not sure if any of that matters.

 

I wouldnt consider it engine braking, and it doesnt come into play when you are accelerating in speed without the engine's help. It only comes into play when you are off the pedal and coasting down(decelerating) and it basically stops the injectors from firing when between those temps and rpm boundaries.

 

Because I am a mpg geek you still suggest against changing these entries? Why is that, if you don't mind my asking?


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In every vehicle I've ever owned it has cut out the fuel injectors when I'm driving to conserve fuel, it also makes the vehicle decelerate quicker when you take your foot out of it.

My 05 Colorado never cuts fuel when coasting but continues to always inject a small amount of fuel even when not under any load or throttle input.

Can we initiate this "feature" with a custom tune or do the newer colorados do this?


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it's safer to always have fuel cooling the cylinders in a "high compression" engine. it's easy to change by vehicle speed and cylinder pressure thresholds in the tune. I've never seen a worthwhile gain or any gain at all in gas mileage when doing this during cruising. why would you want to decelerate quicker? I'd just use my brakes and keep the engine happy.

 

+1 oh you hyper milers...

 

Factory DFCO settings are weak, over rated and overly conservative to say the least.

I picked up about .5-.75mpg adjusting my DFCO aggressively. Been running it aggressively for 150k/3-4 years with no issues. It's all in how you utilize it- I drive 95% interstate, so I use it on off ramps, and it's aggressive enough that when I take hills in 3rd gear (and OD sometimes) around town, coming down hills it kicks into DFCO and I use no gas for those few blocks- it all adds up. You can hear and feel the truck enter DFCO.

I don't claim to be a hypermiler nor do I play one on tv, but I do want every last MPG I can get from my Collie considering I drive 40-50k annually.

As far as cooling goes, you can watch your ECT go down as you are in DFCO- at that point you aren't in condition like PE making power and heat where you need the cooling effect of additional fuel.

 

What is this tuning software that everyone is screencaping? I'm on my phone so it's a little harder to see.


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HP tuners

 

Hpt ftw!!

 

I've got the funds available for a tune. I'm probably going to try one of these mail in services and just request these specific DFCO settings as well as changing my TQ converter locking points.

Also sounds like completely removing TQ Management will help fuel efficiency?

 

Yes to utilize the engines full torque range so you don't have to lay into the power as much to get moving from stops and less downshifting to get up hills using less fuel lower in the rpm ranges


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