How does DFCO work
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TECH Resident
Joined: Aug 2004
Posts: 875
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From: Portland Oregon
How does DFCO work When I run up to 5000 rpm in third gear and lift off the gas, the AFR goes rich for a second or two, then boom it jumps to 22. This must be the DFCO kicking in and shutting off fuel. If I am cruising at 3000 and I lift , my AFR will go 12,11,10,9,8 and stay at 8 until I hit the gas, the DFCO does not work. Is that normal for DFCO to only work when coasting from 4000 or above?? Is that normal for my AFR to be so rich when I decelerate???? When I am coasting my MAP is really low 20 or 25, should I lower my VE in the low MAP area so it will lean out when I lift off the gas??
Yes lowering ve so that it is in the 14:1 area with out DFCO is a good idea. Then you have to change your map boundaries for DFCO enable with your camshaft. You simply are not pulling enough vacuum to enter DFCO at lower RPM's.
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Joined: Dec 2005
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From: Denver International Airport, Colorado USA
Your best bet is to play around with the DFCO Enablers, especially MAP. As the previous poster mentioned, with a cam those MAP's can be hard to hit.
I would not necessarily be over concerned about a perfect match-up of VE and DFCO (depending on your goals). I bumped by enable MAP to match the MAP I get going down a hill (~20-24 MAP). It is all personal preference. I like using it when driving into the mountains. Other people find it annoying.
The bottom line is you have almost total control over it's function. It is normal for AFR's to go 'lean'. The injectors practically shut off as there is virtually no load on the engine. I actually use it to prevent an overly rich decel.
Good luck.
..WeathermanShawn..
I would not necessarily be over concerned about a perfect match-up of VE and DFCO (depending on your goals). I bumped by enable MAP to match the MAP I get going down a hill (~20-24 MAP). It is all personal preference. I like using it when driving into the mountains. Other people find it annoying.
The bottom line is you have almost total control over it's function. It is normal for AFR's to go 'lean'. The injectors practically shut off as there is virtually no load on the engine. I actually use it to prevent an overly rich decel.
Good luck.
..WeathermanShawn..
