Weird ignition timing at 750rpm

[peckhs]

HI, I am very new to DTA,
I have a rebuild Lotus 2.6L 912, and am using the S40 Pro ECU.
I have a base map from the engine builder.
I do not have much knowledge about tuning, but out of curiosity I was looking at the current maps in the ECU.
I have managed to link to the ECU but have not done any logging as the cable is not long enough (I wonder if DTA can fabricate a longer ECU to laptop cable...??)
As the engine does not have a O2 sensor or a MAP sensor, the map was done with reference to throttle position.
I was looking at the ignition map, and am puzzled to see "25.0" at 0% throttle position at 750rpm. Surely that can't be right, as the number is '7.1' at 0% throttle at 500rpm, and '4.0' at 0% throttle at 1000rpm.
I have attached a document file of my Fuel and Ignition map.
Please kindly advise.
Thank you.

[Rob Stevens]

Hi, nothing unusual about that.
The writer of the map has instigated a long-used system to promote stable idle and anti-stall. If the engine speed drops towards 750 rpm the ignition is auto advanced by this setting, therefore the idle will sit somewhere between 1000 and 750 rpm.
However, this is very old school and the S40 has the capability to control the idle speed directly by taking control of the idle using ignition advance when at 0% throttle, you can dictate a target idle vs water temp, takes a bit of setting up but works well.
When the engine is cranking and trying to start this ignition table is not used, the firing is locked at say 1 (this is a setting) crank tooth BTDC, therefore on a 36-1 crank trigger this equals 10 deg BTDC, this is because the engine speed when cranking is very erratic. Once the engine has passed an rpm setting (say750 rpm) the main ignition table is used.
2.6L Lotus 912, nice one, never heard of that large before, what's it in?

[stevieturbo]

It's a crude way of trying to achieve some idle control as Rob says.

But really....again as Rob says, may as well actually used ignition based idle speed control instead.

[peckhs]

Thanks guys.
I will explore the functions more and check the ignition based idle speed control and try it out.

@rob stevens, i do not have the exact specs of the engine yet. Will need to get more information from the engine builder.

[peckhs]

It seems that the idle control using ignition timing is on ?

[stevieturbo]

Some weird numbers in the table.

You'd need to watch the table and see what is happening and what, if any adjustments are being made within closed loop

It makes no sense to have weird numbers in one table, nevermind two.

[Rob Stevens]

Indeed some weird and contradictory numbers and setting there.
But don't worry as it may work just great, is it running ok now?

[peckhs]

Some weird numbers in the table.

You'd need to watch the table and see what is happening and what, if any adjustments are being made within closed loop

It makes no sense to have weird numbers in one table, nevermind two.

Thank you @stevieturbo. I assume you are referring to the idle control table.. Care to explain why you find some of the numbers weird?

I think the tuner did not set the numbers in the 'Base Idle Advance' table as he select the 'Use 20 x 14 Base Duty Cycle Map' option?

I am assuming the Base Idle Advance table is the 20 x 14 Base Duty Cycle Map.

[peckhs]

Indeed some weird and contradictory numbers and setting there.
But don't worry as it may work just great, is it running ok now?

The car idles fine after it has reached about 80°C water temp, but there is hesitation from 2000-3000rpm in 2nd gear onwards.. Once above 3500rpm the car runs great..

I do not have a lambda sensor, so is unable to read AFR.

Correct me if i am wrong, we need a lambda sensor to run close loop right?

The shop seems to have set the lambda to 1 permanently. Not sure how it was done..

[stevieturbo]

Some weird numbers in the table.

You'd need to watch the table and see what is happening and what, if any adjustments are being made within closed loop

It makes no sense to have weird numbers in one table, nevermind two.

Thank you @stevieturbo. I assume you are referring to the idle control table.. Care to explain why you find some of the numbers weird?

I think the tuner did not set the numbers in the 'Base Idle Advance' table as he select the 'Use 20 x 14 Base Duty Cycle Map' option?

I am assuming the Base Idle Advance table is the 20 x 14 Base Duty Cycle Map.

single values, random jump to 100...it's weird.

https://www.dtafast.co.uk/download_file ... Manual.pdf