Can you 'tune' dfco?
Thread Starter
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
Can you 'tune' dfco?
I understand what dfco is, but is that an item that's 'tunable'? What gains are to be had by messing with the dfco, if any?
Thanks for answering my random question.
Thanks for answering my random question.
Thread Starter
Melting Slicks
Joined: Nov 2013
Posts: 2,264
Likes: 3
From: Orchard Park NY
Well I know some cars use it in strange ways... for instance the new McLaren has the dfco setup so that when you let off the throttle at high speeds it sends a fireball out of the exhaust. I'm sure they did that purely for the exotic "whoa!!" impact, but I'm a total noob at tuning and will never attempt to do so, so I figured I'd ask the pro's.
Drifting
Joined: May 2013
Posts: 1,736
Likes: 31
From: Reno Nevada
DFCO is designed to keep the engine from loading up upon deceleration. Some swappers think VSS is not needed, but they quickly find out when the vehicle dies when coming to a stop. I have never found a reason to make adjustment to these values in the constants though.
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
I have no idea if it is a tuneable parameter but my understanding is that it was used to preserve the cats, reduce emmisions and maybe a small fuel savings. I'm not sure if there is anything to be gained by tweaking it. Interesting though.
Safety Car
Joined: Aug 2008
Posts: 4,344
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From: San Marcos CA
Do the smallblock 350's pop and backfire under decel loudly when going lean due to dfco? It is almost insufferable on the LT5's with headers (and even just loud cat-backs), but if it doesn't backfire, I would leave it enabled. If anything due to the fact that you get more engine braking from pumping losses when defueled.
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
Do the smallblock 350's pop and backfire under decel loudly when going lean due to dfco? It is almost insufferable on the LT5's with headers (and even just loud cat-backs), but if it doesn't backfire, I would leave it enabled. If anything due to the fact that you get more engine braking from pumping losses when defueled.
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Melting Slicks
Joined: Jun 2013
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Safety Car
Joined: Aug 2008
Posts: 4,344
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From: San Marcos CA
On the LT5 it is a delayed backfire that apparently is ignited by the sudden lean condition on dfco. I know that "turning it off" made that go away. We are talking about exceptionally loud and embarrassing gunshot backfires- I don't have experience with L98's or LT1's, but I suspect they may be less annoying. What I did to turn it off was to have the minimum speed to engage dfco set to 200 mph or some similar setting that will make it never be able to activate.
Additionally, on the ZR-1's, a similar backfire can occur during the warm up sequence when the air injection is still running (I chose to retain air injection on my headers). It doesn't matter if you disabled dfco- the lean air is coming from the electric air pump. You can avoid the warm-up pops by shifting quickly and/or keeping the throttle cracked open a touch as soon as you get the next gear. This is a little less prevalent if you are running catalysts.
Additionally, on the ZR-1's, a similar backfire can occur during the warm up sequence when the air injection is still running (I chose to retain air injection on my headers). It doesn't matter if you disabled dfco- the lean air is coming from the electric air pump. You can avoid the warm-up pops by shifting quickly and/or keeping the throttle cracked open a touch as soon as you get the next gear. This is a little less prevalent if you are running catalysts.
Team Owner
Joined: Aug 2004
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From: Park City Utah
Drifting
Joined: May 2013
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From: Reno Nevada
Team Owner
Joined: Aug 2004
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From: Park City Utah
Copy that. A light popping/burble doesn't bother me. It seems to me that Mike100 may have a problem though, if he's getting loud reports after going into dfco mode. At that point, there should not be enough fuel to explode.
Safety Car
Joined: Aug 2008
Posts: 4,344
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From: San Marcos CA
It's a special LT5 thing. Remember it's also a speed density system too. Headers cause pops on the 32v engine. There is also a split blm fuel distribution anomaly on them that is pretty much normal for some reason. We just chalk it up as a lack of GM tuning refinement and deal with it by turning off the feature because these cars run so much better with the exhaust and intake mods.
Team Owner
Joined: Aug 2004
Posts: 21,543
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From: Park City Utah
It's a special LT5 thing. Remember it's also a speed density system too. Headers cause pops on the 32v engine. There is also a split blm fuel distribution anomaly on them that is pretty much normal for some reason. We just chalk it up as a lack of GM tuning refinement and deal with it by turning off the feature because these cars run so much better with the exhaust and intake mods.
1. un burned fuel in the exhaust
2. air in the exhaust (usually from exhaust leaks)
3. ignition -from glowing exhaust parts or engine combustion
...doesn't matter the number of valves, MAP, MAF, # of cams etc. My LT1 is MAP, and no backfiring. If you have "gun shots" hen going into or when in DFCO, you've got a problem. First thing I'd ask is, "where is the fuel coming from?"
Race Director
Joined: Nov 2003
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From: Overland Park Kansas
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On L98's, only one bank is monitored (O2 sensor) by the ECM. If the injectors on that bank are leaner than the non-monitored bank, you can get popping during decel. That's because the non-monitored side is dumping more fuel (on decel) than the monitored side.
Checking injector resistance is a good check when you hear excessive popping. Often, you'll find lower resistances on the monitored side.
I tried playing with DFCO once, I wasn't happy with changes from the factory bin -- so I put it back to "stock".
Checking injector resistance is a good check when you hear excessive popping. Often, you'll find lower resistances on the monitored side.
I tried playing with DFCO once, I wasn't happy with changes from the factory bin -- so I put it back to "stock".
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
DFCO (Deceleration Fuel Cut Off) is exactly that -- fuel is cut off. The ECM turns off the injectors during DFCO.
That was a big surprise to me. I had a misfire problem and hooked up LEDs to the injectors. When I took my foot off the gas at highway speeds the LEDs went out.
That was a big surprise to me. I had a misfire problem and hooked up LEDs to the injectors. When I took my foot off the gas at highway speeds the LEDs went out.