Okay so I got my tbi 350 pretty well tuned but have problems when going down a big hill where it will backfire through the exhaust then show up as fully lean. If I tap the gas it goes back to near stoich then repeats the same thing. I have tried adding and pulling fuel and timing and can't seem to cause any improvement. It also seem fine right until 1600 where it begins. Anyway I was wondering if anyone had any ideas to resolve this.

 

Most likely the back fire is from an exhaust leak.

The dead lean may likely be from DFCO.

RBob.

 

My understanding of dfco is that it is the opposite of ae. When there is a negative delta in map the injectors go lean for x amount of time. If this is the case then eventually the afr should go back to near stoich with a little time.

 

DFCO is Decel Fuel Cut Off. The injector PW goes to zero, no fuel.

DE is Deceleration Enleanment. This is where the PW is cut back to compensate for the fuel being pulled from the intake tract walls. And is the opposite of AE.

RBob.

 

Thanks RBob. Never made the distincton between the two. So after doing a little reading it is an emissions thing/ fuel economy feature. Anyway I don't have any stalling or issues like that just the backfire from an exhaust leak. So since I have no running issues there is no issues with running dfco? I just get spooked when I look at the 21 to 1 afr, but running lean when there is no load does not pose any risk for my engine? Please let me know if the statements above are correct.

 

In DFCO there is no AFR. There is no fuel. It isn't running lean, it isn't running at all. The only thing that keeps the engine spinning is the drive train. Do a nice long decel with DFCO active and watch the engine temperature gauge. It drops like a rock.

DFCO is used for several reasons: cat-con protection, fuel economy, and as a secondary feature, to prevent surging on decel.

RBob.