84Elky

Many posts here and elsewhere about not being able to decelerate, car running-on in gear, high RPM before stop, etc. I’ve been faced mildly with this problem for a year or so now and adding a bigger cam recently didn’t help.

But it’s now solved. Can’t believe I’ve been so stupid. Changed all the things mentioned in other posts related to IAC Throttle Follower and it helped a bit, but not a cure. Then shazaaaaam – changed the Closed Throttle Spark Advance .vs. RPM (AUJP $8d) at all RPMs 1200 and above from the Stock AUJP values of 24.96 at 1200 and 29.88 at all RPMs above 1200 -- to 15.12 degrees. Car now decelerates like a manual trans car in any gear. Wow!!! No lean pop, no stumbling, no nothing except deceleration like it should be. Hope this helps.

One more thing -- the SA-TDC reported by TPro logs when decelerating is approx. 3 deg less than 15.12 (12.3). It has always been approx. 3 deg less than the Closed Throttle settings and don’t know why. But that’s a subject for another thread. For now, it slows down big time Yee ha!

87350IROC

iTrader: (2)

Do you not use DFCO? That should solve any decel lean and stumbling issues.

84Elky

Absolutely using the DFCO settings and have optimized them for best kpa and RPMs to begin/end it. But the big difference is that DFCO settings do not appear to alter SA to any significant degree, if at all. They appear to only affect fuel. Haven’t looked at the code to see what’s done with SA, but logs verify no major change. My logs also show that during decel:

• Decel Enleanment is first activated based on (unconfirmed) a drop in TPS % (bit 7 of byte 61 of the DDS = 1 = Decel Enleanment active),
• Injector BPW begins declining during Decel Enleanment, and
• After a few samples when either the DFCO kpa or RPM enable value is satisfied, Decel Enleanment is inactivated, and injectors are turned off (BPW = 0). SA may be affected, but if it is, it’s negligible.

But guaranteed, using the Closed Throttle settings with a low SA values above the idle area is like putting on the brakes during decel. SA-TDC is rock steady during decel at approx 3 degrees below that in the Closed Throttle table (I get 12.3 in every sample .vs. 15.12 in table). RPM is also lower in the 10 MPH area before stopping (on my car, approx. 1050 .vs. 1300+). No longer am I being “pulled” to the stop sign.

87350IROC

iTrader: (2)

It is highly probable that I don't fully understand your situation. But when in DFCO, as you point out, the injectors are turned off and therefore the timing should not matter at all. At least I don't see how it could.

I love DFCO though, so I have it setup pretty aggressive. I have it setup to be in DFCO a lot of the time. So for me, I could only see the timing affecting the decel when at very low rpm or speed.

84Elky

I don't have a situation. Was just posting a solution that helped me that might help others whose car is not decellerating like they would like it to. Many such posts here.

Nope -- Not to argue, but closed throttle is closed throttle, and the decel efffect (can be felt SOTP) is actually more at higher RPMs. Reducing the SA acts like a brake. During decel at any RPM, once TPS % drops below 1.2 % (for AUJP $8d), throttle is assumed to be closed and Closed Throttle SA .vs. RPM table is invoked. Try it. It's just 10 entries from 1200 to 4800 RPM. If it doesn't work you can always change 'em back.

87350IROC

iTrader: (2)

I don't think we are arguing, just have an intelligent conversation.

I think I now understand my confusion. For some reason I thought you had a manual trans. In the case of the automatic, you rarely end up enabling DFCO due to the torque converter. In that case I can see what you are saying, and that would have been useful back in my 700r4 days. Whereas with my manual trans I am basically in DFCO anytime the throttle is closed.

ULTM8Z

So I read this thread and it got me to thinking about DFCO a little more. I hadn't really thought about it since I got it pretty good a couple of years ago.

Pulled up the 93 A4 Trans Am bin ($DA3) and copied the DFCO values over into my $8D verbatim (I figured miniram'd engine should want similar values as an LT1) . I'll be damned! Nice improvement.

Not only does it settle down better when coming to a stop, but it's not fighting against the torque converter any longer while idling. I had it pretty decent before, but I'd still kind of have to apply a decent amount of pedal pressure to keep it from creeping forward (especially since the miniram likes to idle at ~725 rpm).

I didn't think DFCO would have any effect on the idle characteristics when the deceleration finished and the car was at a standstill, but for whatever reason it's impacting the idle (and in a good way).