Did you ever just loose 10 degrees timing? Math?

[EagleMark]

EDIT: Read post 7, conversion is working properly. Main Spark Bias was removed from bin file causing the wrong readings.

You guys may have heard me say a time or to before... "So where did you say your timing was?"

Always check your timing at timing marks and see if it matches up to spark advance table in your mask/xdf. Is it the same? Or is it off by Main Spark Bias?

So the XDF says it accounts for the main spark bias in the Spark Advance table right? Look at the conversion and it says:
0.351563 * ( X - Y )

Where X is spark advance and Y is main spark bias.

Then why are we still off by Y?

Use the eqaution 0.351563 *X
notice no Y argument?
Same timing?

So let's take out the spaces?
0.351563 *(X-Y)
Same timing?

Ok how about:
(0.351563 *X)-Y
Same timing?

So what's the proper equation for 0.351563 *X and then minus Y?

I've tried it a bizillion ways in TunerPro XDF and still same timing.

EDIT: Statement below in bold is incorrect, the XDF conversion is working properly... read posts below to find out why I made a mistake.
FYI anyone using $0D... your timing is off by 9.84 degrees... main spark bias is NOT accounted for in the Spark Advance tables.

[Six_Shooter]

Algebraically, this would be the correct formula: (0.351563 *X)-Y, the main bias would be removed after all other calulations. Also spaces in the formula have zero effect on how a formula works. The only reasons spaces are added is to make them easier to read.

But, the main bias would need to be explicitly written into the equation.

FWIW, I have not not seen a code that needs any sort of offset of the main spark bias to be correct between the table and the crank. I have however seen other offsets case a mismatch between the timing table and the crank. These would include temp compensation, or boost multipliers (if applicable), and similar, that are all used in the SA calcs before boas is removed to be sent to the ICM.

[pmkls1]

FYI anyone using $0D... your timing is off by 9.84 degrees... main spark bias is NOT accounted for in the Spark Advance tables.

In which direction is the timing off from the spark tables ? Are the true timing values 9.84 deg. advanced or retarded in relation to the tables ? I.E. If the cell in the advance table that is active says 20 deg of advance would the actual be only 10.16 deg of advance or 29.84 deg of advance ? This would be assuming that the base distributor timing was set at 0 degrees of course ?

[EagleMark]

FWIW, I have not not seen a code that needs any sort of offset of the main spark bias to be correct between the table and the crank.

$42 spark advace table reads 9.84 degrees higher then actual spark advance because of the bias, as do most mask I have used. This is warmed up and way beyound CTS spark correction.

What's really bad about $42 is small blocks all have 9.84 warm or main bias, big blocks have 0 warm or main spark bias. Both have 20.04 Cold spark bias.

But $0D says

 Title: Main Spark Table vs. MAP vs. RPM (Open Throttle)
Location: 4168
Usage: Spark Advance Tables
Tips: Main spark advance when throttle is open. This table automatically adjusts for L413C "Main Spark Bias". This table represents "Total Spark Advance".  
Conversion: Spark Table - Bias = 0.351563 * ( X - Y )

This is not accurate, Y at L413C is not being subtracted! Spark advace table is still 9.84 degrees higher than actual timing at timing marks. Again warmed up and way beyond CTS spark correction.

True or actuial timing is 9.84 degrees less then spark advance table.

[Six_Shooter]

I use $42 on my bosses '62 Suburban, that has a late model 350 installed, timing was very close to timing tables.

I use $OD in the '71 with the Crossfire, and the timing was not off by 10 degrees, if it was off, it was only a degree or two. I would blame that more on mechanical than PCM/code issues.

What vehicle is this on that you are seeing this?

Different ignition control modules also have different curves built in that affect crank timing, when compared to SA tables, and need to be accounted for.

[1project2many]

Mark, the xdf and cal I'm looking at are displayed correctly. BJYM uses a 10 degree spark bias. The open and closed throttle spark tables are displayed with the spark bias subtracted using Advanced $0d TP5 v2.50. The correct formula is .351623 * ( X - Y ). Verify that the main spark bias is subtracted from the table by opening hex editor, viewing values starting at L4168 (open throttle table) or L428C (closed throttle table). Convert hex values to decimal using windows calculator or other tool then multiply by .351623. In BJYM the spark value at the 400 rpm and 20 kPa cell (both open and closed throttle) is displayed as 20 degrees in TP but is actually 55 hex ($55) which converts to 29.88 degrees. If the math is right and the number displayed is right, you've got an issue somewhere else.

Everything that follows explains why this answer is correct.

Since almost all ecm spark values are equal to hex value * .35163 both the spark table entries and the bias have to be multiplied by .351623. So the actual conversion would be spark table value = .351623 * X - .351623 * Y. As Six said, the rules of algebra determine that multiplication gets done first. Anything in parenthesis is also done first so the previous equation is the same as ( .351623 * X ) - ( .351623 * Y ) although the second version is easier to read. Finally, there are more math rules (the Distributive Property of Multiplication) that say (.351623 * X) - (.351623 * Y) is the same as .351623 * ( X - Y ).

IOW:
.351623 * X - .351623 * Y =
( .351623 * X ) - ( .351623 * Y ) =
.351623 * ( X - Y )

The main spark bias represents the distributor base timing and must be accounted for if the displayed table values are to match crankshaft timing values. This was a big issue at one time on gmecm. Technically all the biases should be included but anything that's looked up from a table or calculated on the fly can't very well be included since it's not a constant like main spark bias.

FWIW, I have not not seen a code that needs any sort of offset of the main spark bias to be correct between the table and the crank.

The ecmguy hac for $0D has clearly labeled the section of code where spark biases are subtracted.

            ; SUB OFF SPARK BIAS VALUES
            ; (RETARD)
            ;
A8C3:            SUBB    L413C              ; 9 Deg MAIN SPK BIAS
A8C6:            SBCA    #$00                ;
A8C8:            SUBB    L413D              ; 20 DEG COOLANT SPK BIAS
A8CB:            SBCA    #$00                ;
A8CD:            SUBB    L413E              ; 10 Deg ALT ADV SPK BIAS
A8D0:            SBCA    #$00                ;
A8D2:            SUBB    L413F              ; 00 Deg EGR SPK BIAS
A8D5:            SBCA    #$00                ;
A8D7:            SUBB    L022E                ; LOW OCTAINE SPK RETARD
A8DA:            SBCA    #$00                ;
A8DC:            SUBB    L0154                ; ??? SPK RETARD
A8DF:            SBCA    #$00                ;
A8E1:            STD     L0220              ; FINAL SPK  ADV

It's also commented in ASDZ for $42:

;
; SUB OFF SPARK BIAS
;
E81B: LE81B TAB ; A to B Reg.
E81C: CLRA ;
E81D: ADDD L0057 ;
E81F: SUBB LD014 ; Main SA BIAS, (10 Deg)
E822: SBCA #$00 ; ROUND
E824: SUBB LD015 ; COOL SA BIAS, (20 Deg)
E827: SBCA #$00 ; ROUND
E829: STD L0051 ; SAVE ADJUSTED SPARK ADVANCE (Temp)

[EagleMark]

Two scenarios, all settings left alone! Just timing table to actaul timing at timing marks on engine. Nothing changed, stock bin file!

In $42 a 5.7L bin file shows spark timing plus 9.84 degrees Warm Spark Bias. In data log and at timing marks on engine it is 9.84 degress less then timing table.

In $42 7.4L bin file shows spark timing plus 0 degrees Warm Spark Bias. In data log and at timing marks on engine it is Actual timing that is shown in spark advance table.

$42 XDF for spark table has no Y in conversion to remove Warm Spark Bias. 0.351560 * X + 0.000000

Idle seems to show the entire Warm Spark Bias, or lack of, as RPM increase it shows less then warm spark bias, still no where near actual. This is do to Spark Latency of GM files being inacurate. Alos the 5.7L and 7.4L Spark Latency settings are different although they use the same EST/ICM module. There's also a couple differant EST/ICM modules that changed around 1992, that change timing at around 3500 RPM... aftermarket modules are even worse!

Back to origanal topic of $0D.... I was wrong and the equation/conversion is working properly! Sorry... The bin file I was helping a guy with had REMOVED the Main Spark Bias, this is the reason the equation did not work, there was no Y, it was changed to 0.0, the entire table was raised by the the conversion working properly!

[EagleMark]

Thanks 1project2many. Your correct, it has noting to do with timing at crank. It is the way the Spark Advance Table appears in the XDF file.

[1project2many]

Don't forget that some cals have additional advance if scantool / cable enables 10k "diagnostic mode." I like to zero out that value if doing a cal for someone else.

[EagleMark]

ALDL mode and 10k still haunts me and I look for it in every log, thank you. It is not on in this log. Does 10K add timing in 8192 baud data like it does in 160 baud?

Just talked to him and not only did he remove the warm spark bias from bin which started this thread... but he has an MSD module, distributor set to 8 advance, no compensation for the advance in ADX conversion... I gained 10 degrees in XDF, got 8 un accounted for in ADX log and I'm still off by 6 somewhere? Can't be off by 6 when he's at 34 total... actually 42 total with distributor base setting... oh my head hurts...

Going to get some sleep and start with base timing tomorrow..., adx data will be accurate then, I know where the 10 came from... still missing 6? I'll bet it's in the module...

[1project2many]

Depends on cal. Most are set up to add timing.

Also can be issues if any spark for idle control etc is added / subtracted after main spark value is saved. Those may never hit the data stream.

[Six_Shooter]

I'm not saying that there aren't offsets and biases that will adjust spark, what I'm saying is that the SA tables have never needed adjusting to match to crank timing (normal warm operation), to match or very closely match crank timing.

I guess I'm just not understanding the issue here?

[1project2many]

In most smallblock and V6 TBI truck cals, GM mismatches the main spark bias and the distributor setting. The spark bias is set to ten degrees but the distributor is factory installed at zero. If the bias and the distributor are matched, like in most car calibrations, there's no need to adjust the displayed value in the spark tables.


My explanation above was incomplete and I apologize. The bold text would have cleared up your questions.

The main spark bias represents the distributor base timing and must be accounted for if the displayed table values are to match crankshaft timing values. When the distributor setting doesn't offset the bias, the constant is subtracted from the tables instead.

[EagleMark]

The names have changed here again. This was never Base Timing or Initial Timing, the setting in bin that has to match distributor.

This is Main/Warm Spark Bias. The one seen is code examples above. These Bias are used so there can be negative number in spark table. Hence the Spark Advance table is off by Main/Warm Spark Bias.... without the conversion in first post.

[1project2many]

The names have changed here again.

What!!!? Waitaminute... I never changed the name. I just mixed it up with another constant. Glad you caught that.

These Bias are used so there can be negative number in spark table.

Positive numbers, not negative. A negative spark value in the table would be misinterpreted by the code as a positive number anyway so the offset allows a way to provide timing less than 0 degrees. And also, I've seen it called a "warm" bias in other places but honestly, it's an "always" bias since it's always used.

I'm off to find a coffee.