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Idle spark table


richardpalinkas
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That gives a brief description of idle spark. Spark is used to control idle rpm, introduce a vacuum leak into the system or change the idle rpm and your idle spark will change in order to try and achieve your desired idle rpm.

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Spark is used to control the idle rpm, if you change your desired idle rpm the pcm will change your spark to help achieve the desired rpm. Vice versa you change the spark it'll change idle rpm. Try changing your desired idle rpm by 100/200 and see what your spark does.

Is there a reason you want to play with your idle spark?

 

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Just experimenting with ghost cams etc, seems as though when the idle dips too low, engine stumbles and causes idle rpm to drop  below idle setpoint. Eg, if my desired idle is 850rpm, when pulling up to a stop, the idle dips back down to 500rpm, before correcting itself. 

 

I've tried altering idle airflow to help, but can't seem to get it where it behaves in a drivable fashion, as the more idle airflow I add, the more idle hang I get, which delays the issue, but is not recitfying it

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On 3/23/2019 at 10:50 PM, richardpalinkas said:

Ok. So desired idle spark is at 60, according to the idle spark desired table, however spark is usually stable around 15 degrees. So which table needs to be modified to say increase the idle spark to say 20 degrees?

Idle spark is PID controlled to reach setpoint. So to get your desired idle RPM it needs 15 degrees, if it was commanding 20 degrees your idle rpm would increase.

So if you want 20 degrees at idle there are two options, increase the idle rpm so it idles higher (and hence commands more spark). Or reduce the idle airflow, so that more torque (and hence spark) is required to obtain the idle rpm setpoint.

The idle air tables are only used on open loop, eg decel or return to idle which is why you see more idle hang and no improvement. Once at idle the PCM also uses a PID to control the airflow. So to reduce idle airflow when in closed loop idle you need to modify the maximum airflow clip. I'm not sure what scalar this is off the top of my head, but I'll look it up when I get a chance.

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