SIMON HOLTBY

Having done a search DFCO is cutting fuel when coasting say down a hill without touching the throttle. So what is decel enlean?

Also how is the fuel cut off. Is is by switching off the fuel pump or the injectors?

Thanks

Simon

RBob

iTrader: (1)

Both cut/reduce fuel through the injectors. DFCO is as you mentioned, long coast-downs. Fuel is just flat-out shut off. (with tapered on/off transitions.) Heh, watch the engine temp drop too. . .

DE (decel enleanment) is in effect whenever (mostly) the throttle is lifted. Has (mostly) to do with the fuel film within the manifold.

RBob.

P.S. General statements required as each ECM mask can/is different.

SIMON HOLTBY

Thanks for your reply Rbob. Refering to DFCO I have set the minimum speed from 15mph to zero. Min rpm to 50 and throttle position to 33%. I can tell it has reduced by a lot although not full stopped gas flow except when I hit the throttle. Which is what I want for my propane powered car. Some gas must have to flow I would have thought otherwise when coasting if the gearbox down shifts the engine would stall.

Simon

Dominic Sorresso

Rbob,

I am in the process of tuning for passing emissions and the problem I have been experiencing is during those small fluctuations in throttle on decel. The dopes that run the car on the emissions dyno don't know how to keep from jerking the throttle up and down. Transitions are not very smooth. From the graphs they provide it appears that HC readings are spiking when they lift off. I have traced part of the problem to the modifications I have made to the IAC control parameters(ie minimize throttle follower, decrease delay factors and such) ad gotten much closer. How would I use the Decel/DFCO and Enleanment parameters to reduce the HC spiking I am experiencing? I am using a 7747 for a TBI motor. Thanks again for your help.

RBob

iTrader: (1)

With the sudden transitions of the go pedal this is not easy. Think of the interior of the intake manifold as a sponge. As the pedal is depressed manifold pressure increases and the manifold absorbs fuel.

When the go pedal is lifted the manifold pressure is reduced and the absorbed fuel is released and the AFR goes rich. This sponge effect is due to the wall wetting (of fuel) on the interior of the manifold.

If the amount of fuel wetting the interior can be reduced, the HC spikes will also be reduced. Heat in the manifold helps (exhaust crossover). Heat the incoming air. Lower the AFR through the O2 windows levels. Reduce the AE. Make a bin specifically for these folks that like to juggle the go pedal.

As you have found slowing the IAC extension will help. The go pedal is lifted but the engine stays revved up slowly returning to idle. Increase the IAC throttle follower. Use the delays. Denatured alcohol (10% - 20%) mixed in with the gasoline helps. Make sure the cat is in good shape.

Additional DE may help. Problem is that the excess fuel is already in the manifold. DE may be too late in the game.

RBob.

Dominic Sorresso

Rbob,

Thanks again. I am attacking this next iteration by continuing to lower the AE for both MAP and TPS differentials. I have also reduced the VE values at the 20kPa cells for all rpms. In comparing some of the stock bins I have with the custom, it appears that the MPH thresholds for VSS coefficients were lower in the stock bin ie the high VSS threshold was set for 42mph while my bin was at 62. The emissions test doesn't go over 60mph.