Ignition Timing Question

[brindo]

Hi,
I am still trying to refine the ignition timing in my VS Series 3 V8, and the indicated timing in Tunerpro is still vastly different to that in the main ignition table. At idle, the table indicates 20 deg BTDC when the actual is 11 deg BTDC. When I increse the timing by 10 deg in the idle table, the IAC position drops 10 steps which to me indicates the extra advance is beneficial.

I have set both the coolant and inlet air temp correction tables all to 0. What do I need to inhibit/alter so that the idle and main ignition tables have no corrections or modifiers?

Thanks

[sparx-1]

Wow. when you state actual timing at 11deg btdc is that taken with a timing light using the marks on the timing case?

[brindo]

Sorry, by actual timing I meant what Tunerpro displayed in the Data List view as opposed to the value interpolated in timing map. Checking with a timing light is a bit of a guess with the factory indicators but it looks to be about 14 to 16 deg BTDC.

Off topic, I have just completed a 1000 km round trip and managed a bit over 27 mpg. Used 47 litres for 460 kms for all highway driving.

[EagleMark]

The difference in timing from main spark table to actual timing is mainly affected by Bias. Not sure how your bin is set up but I
ll give an example. Most bins have 20.04 Cold spark Bias, some have 9.84 Warm Spark Bias and some are 0. There's your 10 degrees if warm spark bias is 9.84.

Every calibration is differant so have to look at and work with what you have, can't take a spark table from one to another without factoring in all the differences in PE, AE, Decel, DFCO etc...

With all the user written XDF and ADX files you have to be careful as someone can include this bias into the mask. We just recently found 2 xdf files, one had bias, one did not. TIming was advanced 10 degrees in entire table!

Then on ALDL data, in the TunerPro ADX file under value of spark advance the conversion would be,
Example: X * 0.352941 + 0.000000 where 0.00000 needs to be changed to Initial Base timing set at distributor. If it is set to 0 and your distributor is set to 5 then your 5 off incoming data. Distributor also needs to be set to Initial Base TIming in bin or max adavnce could be firing wrong cylinder, mostly under deceleration.

There are also Spark Latency settings for EST module which affect actual spark timing. TBI engines have 2 EST modules for small cap that change actual timing and all factory Spark Latency settings are not exact. Large cap HEI is completly differant spark Latency setting. These all have an effect on actual timing.

Inhibiting all corrections and multipliers is a daunting task and can create more issues then solving just to match up Main Spark Table so it looks exactly as acual timing. Leaving these all alone really works well on a street driven car with stock or mild engine, you keep all the built in corrections for cold and hot, warm up and decel etc... knowing where timing is at timing marks compared to Main Spark Table and ALDL datra by doing some testing with timing light is more important along with knowing knock retard is working properly incase you mis calculate.

For example you can add lots of timing to some areas and be fine until you enter PE and add PE Spark!

HTH!

[VL400]

The difference in timing from main spark table to actual timing is mainly affected by Bias. Not sure how your bin is set up but I
ll give an example. Most bins have 20.04 Cold spark Bias, some have 9.84 Warm Spark Bias and some are 0. There's your 10 degrees if warm spark bias is 9.84.

Every calibration is differant so have to look at and work with what you have, can't take a spark table from one to another without factoring in all the differences in PE, AE, Decel, DFCO etc...

With all the user written XDF and ADX files you have to be careful as someone can include this bias into the mask. We just recently found 2 xdf files, one had bias, one did not. TIming was advanced 10 degrees in entire table!

The reason for it is the way GM has written the spark code, it sums everything up and then at the end of the spark code subtracts any retard items. The issue was how to handle a signed tables like the intake air temp table - which needed to add spark when cold and remove when hot. GM did this with a bias value, say this bias is 20deg the intake temp table will have base values of 20deg to effectively have 0 deg of spark mod - Add 20deg then at the end of the spark calc subtract 20deg. Check out the 12P XDF, the charge temp and coolant temp tables have this setup correctly using TP to apply the bias term in the calc. I think what you have found is if the bias term and the base value of the spark modifier table are different you will see a heap of advance or retard - you are correct, have to be very careful when setting this up or copying tables!

Then on ALDL data, in the TunerPro ADX file under value of spark advance the conversion would be,
Example: X * 0.352941 + 0.000000 where 0.00000 needs to be changed to Initial Base timing set at distributor. If it is set to 0 and your distributor is set to 5 then your 5 off incoming data. Distributor also needs to be set to Initial Base TIming in bin or max adavnce could be firing wrong cylinder, mostly under deceleration.

Its not this way on aussie bins and didnt think it was on US bins either, so long as your software ref angle matches the actual ref angle (or base timing) of the engine then what is displayed in TP will be = to delivered. You do not need to change the spark calc.

[brindo]

Hi,
Not sure I understand much of the above two posts as they are way above my understanding.

If I return the intake air and coolant temperature correction tables back to normal and keep increasing the main table till I find the highest manifold vacuum, the table would have timing figures around the around the 35 degs BTDC for idle. The only other option to get the actual and displayed timing to match is to change the distributor base timing?
I also have made both the high and low octane tables the same while I make changes.

[Holden202T]

have you put the computer in diag mode and made sure the dizzy is in the same spot as the reference angle is commanding ?

[brindo]

The distributor is set to 10 degs BTDC in diagnostic mode. Is there another method to setting the distributor position?

[VL400]

Its possibly idle spark adjustment thats also making changes when idling. The PCM uses spark advance as well as the IAC to stabilise the idle speed, if your idle speed is different to the target it can add/remove a fair bit of timing (adds timing when RPM is lower than target and removes when above target). If you edit address 3C61 from 0x0F to 0x00 it will make the maximum idle spark adjustment 0 deg.