DuronClocker

iTrader: (1)

Again, it appears these two items (Deceleration Fuel Cut-Off) and Deceleration Enlean would contradict each other's reasons for being. Never realized there was an item to enlean on the decel.

I failed emissions for HCs (reading .98, limit .80) and the biggest spike in HCs to 3.0 was on a section of deceleration, so I figured my DFCO settings weren't all that great. However, I see the decel enlean. What are the reasons for having this, and should I set it much lower?

RednGold86Z

iTrader: (1)

Decel enlean is basically the opposite of acceleration enrichment, where sensor lag, and manifold wetness have to be counteracted when going from high load to low load - throttle in the act of closing.

Decel cutoff is when coasting in gear off the throttle where the load is so low that the Pulse widths are below the usable limit (innacurate or not injecting fuel at all), and compression and ignition timing cannot support stable ignition. Decel cutoff also helps fuel economy.

The two features aren't really related, and decel enlean doesn't appear to be used in the $6E from the factory, although it can be enabled.

Decel enlean did not cause your emissions failure, as the tests are steady state, and decel enlean is a transient feature.

Reducing ignition timing is always my first suggestion for emissions failure. It helps heat up the exhaust and make a tired cat work a little better. It also reduces misfire in general, and supports complete combustion under lower loads.

Try taking out 5-10 degrees in the load regions on the test, and even though it will degrade drivability, it will almost certainly help emissions.

Good Luck

DuronClocker

iTrader: (1)

Hmmm interesting I thought retarding timing helped NOx and hurt HCs while advancing timing helped HCs and reduced NOx.

My NOx isn't even tested, but my HCs are. I replaced the cat and spark plug wires and re-gapped the plugs (I know, I should've just bought new ones, but now I'm hoping to just wait til I get new heads and headers on before changing them), and it dropped the HCs from the original 2.34 to .98. COs dropped from 44.6 to .1 and limit is 15.0.

I'm going to throw some alcohol in the tank next time I go (what kind, does isopropyl work?) and mess with timing a bit I suppose. Shouldn't take much to pass now..