CM849 Cranking Timing

biggy238

biggy238

Active member
Throwing this out just in case someone knows.

I want to know what the ECM uses to switch between the cranking timing table and the main timing table. It can't be engine speed based because they overlap.


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biggy238 said:
Throwing this out just in case someone knows.

I want to know what the ECM uses to switch between the cranking timing table and the main timing table. It can't be engine speed based because they overlap.
Click to expand...

I could be wrong, but I believe it's tied in with rail pressure. Rail pressure reaches desired cranking pressure, engine fires, and then the injector return signal goes to throttle based run RP and timing.
 
Snedge said:
I could be wrong, but I believe it's tied in with rail pressure. Rail pressure reaches desired cranking pressure, engine fires, and then the injector return signal goes to throttle based run RP and timing.
Click to expand...
Excellent. I think part of my rough start is me ignoring the cranking timing.

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I could whip up a tune with much higher main timing in the cranking range and log it to see when it transitions.

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Hmmmm

Well, according to my test, The ECM utilizes the idle timing table for any RPM value under specified idle speed. It did not shift to the main timing table until it crossed 800RPM.
 

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biggy238 said:
Well, according to my test, The ECM utilizes the idle timing table for any RPM value under specified idle speed. It did not shift to the main timing table until it crossed 800RPM.
Click to expand...

So, as far as timing goes, idle map, and cranking map are one and the same ?
 
Snedge said:
So, as far as timing goes, idle map, and cranking map are one and the same ?
Click to expand...
No sir, The cranking timing map is in use right up until the idle RPM threshold is crossed, and then it switches to main timing. In my screenshot it changes right at 810rpm.
I had it set to switch from 5 degrees on the cranking timing to 12 degrees main timing so that there was a clear change.

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Last edited:
biggy238 said:
No sir, The cranking timing map is in use right up until the idle RPM threshold is crossed, and then it switches to main timing. In my screenshot it changes right at 810rpm.
I had it set to switch from 5 degrees on the cranking timing to 12 degrees main timing so that there was a clear change.

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Click to expand...

Got it. Thanks for the information.
 
Snedge said:
Got it. Thanks for the information.
Click to expand...
I've nearly self destructed. I tried to migrate my tune from an auto file to a manual base file and it absolutely refuses to run on tune 1. I've copied tables from 3 other know driving tune files and it just can't run.

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