HELP! Throttle blip issue...settling back to idle

[kjlindgr]

Guys,

I'm having an issue with what appears to either be a fueling or spark issue when I blip the throttle and it tries to settle back in to idle. As it comes back down, spark ramps back in, the engine shutters/chugs/shakes, and then it finally ramps out and all is well again. I've got a log and my tune file attached as well as a picture of the problem area.

Just as an FYI, this is after a cam and NW102 throttle body only install. It was running great prior.

Here are my thoughts, but I'm not familiar enough with programming this to figure it out or where to start:

1: I see that it is dead lean, so is this a minimum idle airflow issue and it's trying to save idle by ramping in spark? Or doesn't fueling matter as it's coming back to idle??
2. I was told it could be a throttle follower issue, but I've played with these tables and can't get it to act much differently.
3. I've tried to limit the idle low rpm correction tables and I still can't seem to control this.
4. This is completely normal activity and there is another issue I'm completely overlooking...

Any help on where to look? Any ideas if it's a fueling issue I should be running after or a spark issue? I'm really lost here guys... :(


Video showing what's happening:
http://www.youtube.com/watch?v=jqkXH98Npas

Log File:
shuttering 3.efi

Area in the log file where this is happening:


Tune file:
Texas Speed Tune_with changes follower_0019.ctz

[joecar]

Comment: MAP looks incorrect.

Is there any way to try the previous throttle body...?

[kjlindgr]

I've contemplated tossing it back on. I have the throttle body, but I don't have the coupler any longer. I guess I could just run some tape around the end to seal it up. I can try this.

[kjlindgr]

I quick ran out to the garage to give the old throttle body a try. I tried two tunes. The first one with all the changes I've been making. The second was the one I pulled off the car immediately before the cam install. Both gave me very similar results with the chugging and plug fouling coming back down to idle. I've got a picture of the MAP placement on the Fast 102. I even sprized some carb cleaner around the gasket when it was idling to check for leaks and got nothing.

I'm actually at a point where even if I were to swap everything back, I highly doubt it would run like it did before. Something happened. I just have no idea what. :(


MAP placement:

[kjlindgr]

I did a ton more logging and here's what I'm noticing. I logged injector pulse width and started comparing that against AFR. At a steady idle at about 14.6AFR it's commanding about 2.6ms injector pulse. It seems that there's a pretty consistent 10 frame delay between pulse width changes and the impact this has on AFR. Sweet. Now comes my issue...only during this rev down period does this not apply. In the example I've attached, I count over 60 frames between where it is back commanding 2.6ms of pulse width and a 14.6AFR wideband result. The majority of the time it's dead lean pegged at 16.0...which after a while it starts to stumble, chug, and ramp in spark to compensate for the drop in RPMs.

Now the question for all of you guys...what is causing this lack of response ONLY in this area?? I'm running pretty new NGK TR6 plugs which might be a bit cold for this car, but I tossed them in because they were new and these tests were done with the car fully warmed up. I tried increasing coil dwell 0.5ms in this RPM and volt range to see if I could get a bit more power in the spark, but that didn't do anything. For now, it seems that I simply can't control the fuel in this area...although the ECU is trying...which is in turn causing all my issues.

Any help on this one?


Difference in response by frame count:


Log File:
blip 15.efi