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spikeygg
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Engine Start Detail

Hi guys, I've been trying to figure out how the engine start stuff works together and it seems there is limited data available. I understand that there are three major contributors to engine starting:

  1. Initial Crank Pulse
  2. Crank Injector Time
  3. Start Extra vs Temp/Decay

I'm having a hard time understanding the sequence of things. Here are some questions that I have:

  1. Does "Stat Sync'd" govern everything? I mean does "Stat Sync'd" have to be ON in order to even get an "Initial Crank Pulse"?
  2. I understand that the "Crank Injector Time" allows me to floor the pedal while cranking to clear the engine but when I do this does the EMS still fire the "Initial Crank Pulse"?
  3. Does the "Start Extra vs Temp" apply to the "Crank Injection Time"?
  4. Does the "Start Extra vs Temp" apply to the "Initial Crank Pulse"?
  5. Does the "Warm Up Enrichment" apply to cranking?

I don't know for sure but because both ICP and CIT are measured in time (ms and us, respectively), I think that the ICP is fired when "Stat Sync'd"=ON, then after the ICP as the engine is turning the EMS applies the CIT. I still don't know where the "Start Extra vs Temp" and "Warm Up Enrichment" comes in. Can someone please explain how this works? Feel free to use equations. :)

 

Thanks,

-Greg

AEM_NS
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Stat Sync'd must be ON before

Stat Sync'd must be ON before there can be any spark or fuel output, including ICP.  ICP is not affected by the CIT table values so yes, even if CIT is zero, ICP is still delivered.  The Start Extra fuel is not applied until after the until is running.  CIT is affected by trims such as Warm Up Enrichment, Boost Comp, etc.  Start Extra fuel is multiplier that's decayed out based on time and Warm Up Enrichement is a multiplier based on coolant temp.  

You can see how all this works by taking logs during cranking/starting. 

Kurt
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Below the rpm value in the

Below the rpm value in the Crank Max RPM option, the AEM is in "cranking" mode and the base IPW value comes from the Crank Injector Time table.  All the modifiers all apply to that value.  With the option Crank Inject All = ON, Initial Crank Pulse happens imediately after Stat Sync'd, then you get sequential injections after that.

The sequence starts immediately after sync.  All injectors fire at this point for the amount of time in the ICP table.  If this time is over 52ms then there are two pulses (52ms + remainder).  No modifiers are applied to this.

After the ICP, sequential injections are fired.  The base pulse width is pulled from the CIT table, not the fuel map.  During cranking, every modifer is applied to that base value, just as it is above the Crank Max point.  If the CIT value is 2ms, then the final pulse width will be 2*(boost*warmup*air temp*baro*start extra*ect..) + injector offset.  Every modifier applies. The Start Extra modifier remains at the initial value during cranking and will start to decrease when rpm goes above the Crank Max value.  The rate that this is pulled out comes from the Start Extra Decay table.  

I studied fast internal logs to learn exactly what's going on with the IPW calculation.

 

 

Edit: sorry Nate.  You replied while I was typing. smiley

AEM_NS
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No worries.  You proved my

No worries.  You proved my point that this can be seen in logs.  

spikeygg
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[quote=AEM_NS]

AEM_NS wrote:

Stat Sync'd must be ON before there can be any spark or fuel output, including ICP.  ICP is not affected by the CIT table values so yes, even if CIT is zero, ICP is still delivered.  The Start Extra fuel is not applied until after the until is running.  CIT is affected by trims such as Warm Up Enrichment, Boost Comp, etc.  Start Extra fuel is multiplier that's decayed out based on time and Warm Up Enrichement is a multiplier based on coolant temp.  

You can see how all this works by taking logs during cranking/starting. 

 

Thanks Kurt and Nate, I saw this note in the "Tuning Explanation" tab under "Function Explanation" and it threw me off. :(

Depending on the coolant temp, the cranking injection pulse will be increased by a percentage (Start Extra vs Temp). The duration of this extra cranking fuel is based on temperature and is pulled from the Start Extra Decay table. 

 

It must be saying that this only applies above the Crank Max RPM when the full 3D fuel map is being utilized not the CIT table, right? 

What you've said makes lots of sense now.

Kurt
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[quote=spikeygg]

spikeygg wrote:

Thanks Kurt and Nate, I saw this note in the "Tuning Explanation" tab under "Function Explanation" and it threw me off. :(

Depending on the coolant temp, the cranking injection pulse will be increased by a percentage (Start Extra vs Temp). The duration of this extra cranking fuel is based on temperature and is pulled from the Start Extra Decay table. 

 

It must be saying that this only applies above the Crank Max RPM when the full 3D fuel map is being utilized not the CIT table, right? 

What you've said makes lots of sense now.

 

Log the channel Start Extra and you will see exactly what it's doing.  This is applied during cranking and will start to decrease after leaving "cranking" conditon.  Watch the channel Stat Cranking.  Pretty much everything the AEM is doing has a channel.

 

BTW, these replys in the middle of a thread are kinda wacky! lol