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DFCO changes and affects

This is a discussion on DFCO changes and affects within the Computer & Tuning forums, part of the LSx Technical Help Section category; Now that I've had some drive time and fuel mileage figures I thought I'd share. DFCO is definately worth tinkering ...

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    Moderator Firebirdjones's Avatar
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    DFCO changes and affects

    Now that I've had some drive time and fuel mileage figures I thought I'd share. DFCO is definately worth tinkering with.

    My 6.0 blazer just reported it's best MPG around town yet with the 3.73's and DFCO tuning.

    With no DFCO changes and 3.07 gears, it would consistently get 16 mpg around town. Once switching to 3.73 gears I consistently got 15 mpg around town, and tickled 16 only once.

    Changed the DFCO settings around so it would come on more often and stay on longer (it barely worked at all before due to the high rpm settings) Now I'm consistently getting over 17 mpg around town driving. So there was a solid 1.5-2 mpg change for the better.

    My wifes SS camaro showed the biggest gains. It was originally set to come on at 1900 rpm. That's a cruise rpm I never hit, so assentially the DFCO wasn't working. I made similar changes to the camaro that I made to my blazer, which not only allowed me to hit DFCO more often, but it's actually working now on this car.

    Consistently 21 mpg around town driving in this car, I just filled up and got a whopping 25.2 mpg with same driving habits. I couldn't believe it. I'll run another tank through this car to confirm, but as of right now, DFCO is worth tinkering with.

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    Nice. Thanks for sharing.

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    Details on what changes you made to it?

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    Moderator Firebirdjones's Avatar
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    Oooops, I lost track of this thread. I don't always get email notifications, sorry

    On the changes, I basically just made DFCO come on more often,,,or in my wife's camaro's case, made it come on.

    I changed the rpm activation and deactivation tables. On the camaro (not sure if this is all Fbodies) it wasn't set to come on until 1900 rpms in every gear. I believe that's stock but not certain. Jeff, you have HPtuners correct? Maybe you could look in your file and verify?

    In any event, with a 6 speed and 3.42's, I never hit that cruise rpm. 1900 rpm in 6th is 85 mph, I don't drive that fast so it never came on even though it was turned on in the tune. I think it turns off at 1100 rpms.

    What I did was lower that activation rpm to 1300 so it comes on sooner, and then lowered the deactivation rpm to 1,000 rpms. This way DFCO comes on more often and stays on a little longer. Here is the only caution I can recommend at this time, lowering the deactivation rpm any lower than 1,000 may cause the car to have issues coming back to idle. Depends on alot of things, but my wifes car has a mild cam and that was one issue. I have idle set at 800 rpms so I couldn't get too close to that setting or it caused surging and sometimes would die. So I left the spread at 200 rpms and that seems to work just fine, giving the engine enough time to recover from fuel cutoff.

    The 6.0 truck tune in my 72 blazer was the same way but not as bad. It came on at 1600, but again, I never hit that rpm cruising with 3.07 gears and 33" tires. Now with 3.73's it does, but I lowered the rpm to 1300/1000 in that one also. Now it comes on sooner and stays on longer.

    Getting back to the 4th gen, I'm still playing with it. I found that DFCO doesn't work during clutch transitions (aka: shifting through the gears). So you have to be in your gear and let off the gas (without clutch) for DFCO to activate. I'm playing with that clutch table now to see if I can tickle DFCO during shifts. Just that little extra bit all adds up. This is where the auto's may have an advantage.
    Another table I want to play with when I figure it out, is how long it takes DFCO to come on after you let off the gas. I can feel it activate, but takes about 3-5 seconds after letting off the gas. I'd like to make it more instantanious. Haven't figured that out yet but there has to be a time setting table somewhere. There are alot of things to change in DFCO, I've only begun to tinker. I'm liking the results so far. It comes in handy around here in mountain terrain.
    Last edited by Firebirdjones; 04-12-2012 at 11:22 AM.

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    Moderator Firebirdjones's Avatar
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    Oh just to add, I ran another tank of gas through my wifes camaro, 24.3 mpg on that tank with just around town driving. So I don't believe that first tank was a fluke now That's close enough for consistency sake.

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    Not that I know what I am doing with it, but yes, I have HP Tuners.

    I checked my DFCO settings and the "Enable DFCO" table is all set to 1500. The "Exit DFCO" table is all set to 900. Only other DFCO tables I see are associated with barometric pressure.

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    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Not that I know what I am doing with it, but yes, I have HP Tuners.

    I checked my DFCO settings and the "Enable DFCO" table is all set to 1500. The "Exit DFCO" table is all set to 900. Only other DFCO tables I see are associated with barometric pressure.
    Ah okay, yours is an auto correct? I wonder if the auto's have a lower activation rpm setting than the 6 speed cars do??

    Wait a minute, I have an auto file here from my own 02 SS, let me look at that DFCO and see what it is. My wifes 6 speed was 1900, I thought that was bizzar for a double overdrive car with 3.42's that never see's that cruise rpm.

    If your's comes on at 1500, even with stock 3.23's you should hit that no problem with an auto while cruising around. You could lower that to come on sooner and you might find some mpg. If it shuts off at 900, it will be interesting to see how that acts when a camshaft goes in,,,hint hint

    Mine was a little fussy but not bad. I just couldn't have ANY issues pop up because it is my wifes car after all, and I don't want issues while she drives it, so I couldn't get real aggressive with the shut off rpm.

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    Our car is an A4. We have a 12 bolt with 3.73's out back and it is running a Frost mail order tune. I don't have my stock tune file anymore, so not sure what the original settings were. Cam and heads are probably the next big mod for her -- I have everything else about where I want it now. Hoping to get some traction this weekend so I can maybe best last year's 12.43.

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    Good luck with it Jeff. I'll look at my stock 02 file and report back.

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