DFCO, What is it good for?

[Mark Romans]

Mike, I have an 87 Vette and I fought a stalling condition for quite a
while.  It was several things.  It started when I raised the idle speed in
the prom and changed a few things on the spark map.  Talk about unintended
consequences!
1)You need to make sure that the spark map at light throttle transitions
smoothly downward in deg of spark advance.  If there is a big drop the IAC
retracts trying to bring the idle speed down and then the ecm pulls out 20
deg of timing and the IAC has to add air to try and catch it and nope,
stall.
2) When I raised the idle speed, the enable rpm for hwy spark was 800 rpm's.
I set the idle at 900.  So at a nice steady idle, suddenly the ecm would add
another 8-9 deg of spark.  IAC would retract trying to keep the idle at 900,
I could just brush the clutch against the flywheel, LV8  (Calculated load
value would go up) and the ecm would pull out the hwy spark and voila, not
enough air and the engine would stall.
3) Stall saver parms were too low.  Had to reset all those.
4) DFCO,  it would stay enabled to too low an rpm.  Stall.  Also with 11.1
to 1 compression the load values changed and at less than 3% throttle at say
25 mph around town in 2nd gear, at a steady state rate of speed,  DFCO would
suddenly decide to kick in.  JERK JERK.
Had to lower the enable value.  Also had to lower the resume.  (Hysterisis
pair).
I discovered all this with some help from a few people on this list. After
spending a TON of time trying to resolve it playing with the PID that
controls the IAC.  (Waste of time).
Unfortunately non of this stuff applies to your app if you don't know what
the addresses are.  It took many months to back into most of the above
education.
Mark
There is a lot more involved than you think.


-----Original Message-----
From: Mike Pitts <mpitts at emi.net>
To: gmecm at efi332.eng.ohio-state.edu <gmecm at efi332.eng.ohio-state.edu>
Date: Saturday, March 20, 1999 9:10 PM
Subject: Re: DFCO, What is it good for?


>>Some time ago was a thread about my comments about setting things up with
>>min IAC counts, and I was taken to task for that statement.
>>Is there a way to raise the anti-stall rpm on the 148s?.
>
>
>I've don't recall a specific anti-stall section in the cal.   It's probably
>not labeled as such, but rather IAC recovery rate or something.  I'll
>have to take another look.
>
>I personally have never had any luck messing with the IAC count or
>rate stuff myself.
>
>This about-to-stall situation happens at the same time as I've seen the
>O2 LED bar meter go to zero in a friends car.  That's why I think it's the
>DFCO.
>
>I noticed in the cal that DE is set slightly leaner when the TCC is locked
>up.  I gather from this that decel can go leaner if there is sufficient
>engine
>braking occuring from the force of the trans.
>
>Since I don't have a TCC anymore and my converter is a light 9", and
>since cars with 9" converters tend to stall easily, I'm guessing the engine
>is leaning out too much during decel.
>
>-Mike
>
>