U4P2 Idle Spark Behavior

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Killer95GT302
Posts: 21
Joined: 2021 Dec 29, 08:21
Location: Annapolis, Maryland
Vehicle Information: 1995 Mustang GT U4P0

Single Turbocharged 363

Tuned using Tweecer with Binary Editor

U4P2 Idle Spark Behavior

Unread post by Killer95GT302 »

I was going thru an idle behavior issue with the U4P2 tune where it would sit at feedback min clip (SPK_FBS_MIN set at 10 in the U4P2 tune).

With the U4P2 tune, the combination of spark values never allowed for the EEC to play with timing to stabilize idle.

Feedback Spark Desired Torque (SPK_LOAD_RES) in U4P2 was changed from the stock .05 to 1.35. The U4P2 value when looked up against Spark MBT Retard for Torque Limiting (FN799) always came up with 0 which didn't allow any Feedback Spark Gain when RPMs dipped below the set Idle values. I changed this back to stock.

What this led to was (keep in mind I have a non-stock turbo cam) idle sometimes dipping below the set RPM values and then a sudden surge as the EEC added timing to stabilize it. This was different from stock behavior where it appears to constantly modulate timing, ISC and Fuel to keep it steady. Honestly, the stock method held a much steadier idle, and sounded healthier so I investigated which values I had to change to make it behave like that.

Spark MBT table (FN2300) was scaled with a minimum of 1250 RPM and 30 load, which was beyond the stock min values where my idle RPMs and load sit. I changed these scalers back to stock minimums while leaving the higher load scale values and filled in accordingly. I had to change the other impacted tables by the scaler values as well.

I changed SPK_FBS_MIN to 20. This clipped timing at a minimum of 20* at idle.

The result was a much healthier sounding and less fluctuating idle which eliminated the sudden timing surges to stabilize to idle RPM settings. Instead of sitting at min clip, the timing is constantly modulating between 20 and 25 degrees along with minor ISC and fuel changes. The idle deviates much less from rpm values than before.

@decipha I'm curious to know was there something I'm misunderstanding with the U4P2 values in the downloadable tune or was there additional theory around getting a stable idle while timing sat at min clip and only allowing ISC and fuel to stabilize RPM? To me having timing aid in the stabilization makes it run much smoother.
decipha
Posts: 4953
Joined: 2021 Feb 15, 12:23
Location: Metairie, LA
Vehicle Information: Work Truck
'19 F-150 3.3L

Re: U4P2 Idle Spark Behavior

Unread post by decipha »

If you were riding the minimum clip then obviously your idle air is off.
Killer95GT302
Posts: 21
Joined: 2021 Dec 29, 08:21
Location: Annapolis, Maryland
Vehicle Information: 1995 Mustang GT U4P0

Single Turbocharged 363

Tuned using Tweecer with Binary Editor

Re: U4P2 Idle Spark Behavior

Unread post by Killer95GT302 »

Thanks I will take another look at idle air to see where I might have gone wrong.
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