Quick question.
I understand that when in PE mode, the table at 15E is added to the other spark parameters to give the total advance amount.. etc...

I have just stumbled across a "PE spark Advance Amount" parameter at 2A. Its just a single element parameter.

Is this also added to total advance, at all rpms, when in PE mode???

Thanks,
Ben.

 

There also a spark slope.
It begins at a given rpm, and adds a given amount of spark per thousand RPM. It allows for adding timing past the end of the spark table. Just like the VE #2 table allows for modifing the fuel curve at higher then the table would allow.

 

Thanks Grumpy,
I am aware of the slope beyond 3600rpm using the 'degs/1000 rpm' parameter at hex 0D, up to max slope rpm at hex 0C..

What can you tell me about the value at 2A??

Thanks,
Ben.

 

I've had a look thru the hac, but this is not something i am good at interpreting...
The only references to 02A I can find are:

;---------------------------------------------
; HIWAY SPARK ADDER QUAL'S
; QUALS FOR SPK ADDER TBL LD157
;---------------------------------------------
LD024 FCB 96 ; 30 MPH, HWAY SPK ADV QUAL Thresh MPH, MIN
; VAL = MPH * 3.2
;
LD025 FCB 40 ; 40 Sec's HWAY SPK ADV QUAL MIN TIME Thresh (SEC/1)
;
LD026 FCB 9 ; 2 SEC'S, SPK Time out reduce, (Sec * 5)-1))
LD027 FCB 40 ; 40 SEC'S, PWR ENR SPK TIME OUT
;
LD028 FCB 112 ; 2800 RPM, MIN RPM FOR SPK SA DECAY
;
LD029 FCB 39 ; Pwr Enr SPK Decay cool THRESH
LD02A FCB 2 ; Pwr Enr SK ADV INCREASE, Deg, 1.4 Deg
;---------------------------------



AND



ED6F: LED6F ORAB #$02 ; SET b1
ED71: STAB L000D

ED73: LDAB L006E ; PWR ENR SPK
ED75: ADDB LD02A ; Pwr Enr SK ADV INCREASE, Deg, 1.4 Deg
ED78: BCC LED7C ; BR IF NO OVERFLOW
;
ED7A: LDAB #255 ; FORCE MAX VALUE
ED7C: LED7C STAB L006E ; PWR ENR SPK

ED7E: LDAA LD026 ; 2 SEC'S, SPK Time out reduce, (Sec * 5)-1))
ED81: LED81 STAA L006F ; PWR ENR SPK TIMER

ED83: LED83 LDAA L0058 ; COOL (INV)

ED85: LDAB L0001
ED87: BMI LEDDA

ED89: LDAB L00DE ;
ED8B: BITB #$08 ; b3
ED8D: BNE LEDBA ; BR IF b3


It looks as though the value at 02A is added to the PE spark advance in lines ED73- ED75 above??
Am i reading this right??

 

What GM is doing is to attack the PE SA in. Once the ECM enters PE mode the PE SA will get added to the current main SA. If this is done suddenly, all 5-6 degrees (or whatever it is) at once then knock can/will occur.

Plus, it can be felt as a sudden jolt. Not a smooth transition at all.

So, GM adds in a little at a time until full PE SA is available. Makes for a smooth transition along with allowing the extra fuel to flow (lower commanded AFR) and get to the chambers before the extra SA comes in.

RBob.

 

So is this value at 02A the number of degrees advance added during PE, or is it an attack rate that limits the rate at which PE advance is added according the the PE spark table at 15E ??

 

Attack rate. I didn't look to see how often it is added. Notice how it will go to 255 and be held there. The PE SA routine checks to see which is lower: desired PE SA, or the accumulated attack value, and uses the lower of the two.

RBob.

 

Thanks RBob!!

 

The PE advance in the truck ECM is interesting. It uses the PE Advance table value as-is from the start of PE mode. When the conditions are met, it then times out a timer, and begins removing PE advance over time. The address 0x2A value is the increment to the value that reduces the PE table advance value.

The following may help:

*
* PE Mode Advance Decay
*
PeRetardTmrInit FCB $09 ; Timer value for retard increments
PeAdvTmrInit FCB $14 ; Timer value for 1st pass 20 Sec
PeRetResetRpm FCB $64 ; Reset PE retard if under this RPM
PeRetardEct FCB $27 ; RawEctNv to allow PeRetard
PeRetardInc FCB $02 ; PE retard incrementor

The PeRetardInc is the 0x2A value that you noticed. The initial time for any PE advance reduction is at PeAdvTmrInit, and it is in seconds. The PeRetardTmrInit is the time between further PeRetardInc additions. It is added at a quicker rate, 5 times/sec, until the PE advance is reduced to zero. Not sure why this clever use of PE advance was dropped.

Scot

 

I've tried to follow Grumpy's rules for tuning, ie I don't depend on the adders. So the Spark Slope is gone and the PE advance is set to 0. All the spark timing is in the SA table except for things like cold cranking.