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Old 09-27-2023, 10:09 AM   #1
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CM849 Cranking Timing

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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Old 09-28-2023, 07:05 AM   #2
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Quote:
Originally Posted by biggy238 View Post
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.
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.
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Old 09-28-2023, 09:13 AM   #3
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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.
Excellent. I think part of my rough start is me ignoring the cranking timing.

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Old 09-28-2023, 10:19 AM   #4
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Excellent. I think part of my rough start is me ignoring the cranking timing.

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Hope that's the ticket. It's only my semi educated assumption.
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Old 09-28-2023, 12:25 PM   #5
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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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Old 10-03-2023, 08:20 PM   #6
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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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Old 10-04-2023, 07:10 AM   #7
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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.
So, as far as timing goes, idle map, and cranking map are one and the same ?
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Old 10-04-2023, 08:46 AM   #8
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So, as far as timing goes, idle map, and cranking map are one and the same ?
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 by biggy238; 10-04-2023 at 08:48 AM.
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Old 10-04-2023, 03:22 PM   #9
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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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Got it. Thanks for the information.
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Old 10-04-2023, 08:12 PM   #10
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Got it. Thanks for the information.
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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