Cranking RPM and the process of starting - Miata Turbo Forum - Boost cars, acquire cats.

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Old 09-09-2011, 10:36 AM   #1
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Default Cranking RPM and the process of starting

My DIYPNP is gradually getting closer to starting like stock, but I'd welcome any advice about the process the ECU goes through when starting the car.

This morning the car took about 2 seconds to fire, but then ran smoothly.

Stepping through the log, it took about 0.3 seconds for any rpm to register and that's when Cranking:Y lights up. Run:Y lights half a second later (but I don't see what triggers that). Fuel injection starts 0.3 seconds later. Another 0.3 seconds later it hits 300rpm and fires up cleanly on the next stroke.

For most of that time, I can see it it was cranking at about 250rpm. My Cranking RPM is still set to the DIYAutoTune default 300rpm. Is there any reason I shouldn't reduce the value to 250rpm to speed the process? (Or is 250 actually rather low, and should I look at my battery, ground wiring etc? When cranking, the voltage drops to around 10V. Is that low?)
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Old 09-09-2011, 10:37 AM   #2
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you should increase it if anything. You'll have trouble starting if your battery is low or it's a cold day.

the delay is the MS confirming the crank inputs and syncing.
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Old 09-09-2011, 11:16 AM   #3
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you should increase it if anything. You'll have trouble starting if your battery is low or it's a cold day.

the delay is the MS confirming the crank inputs and syncing.
Sorry, I don't follow you. Are you saying I should increase Cranking RPM value or that I should try to improve the speed my starter motor turns the engine?
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Old 09-09-2011, 11:42 AM   #4
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the delay is the MS confirming the crank inputs and syncing.
This confuses me. How does the MS know it's cranking before it's sync'd?
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Old 09-09-2011, 11:55 AM   #5
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Sorry, I don't follow you. Are you saying I should increase Cranking RPM value or that I should try to improve the speed my starter motor turns the engine?
If the cranking RPM value is too low, you'll have trouble starting...mostly in cold weather or on a sub par battery. Say you lower it to 200RPM and you get it to crank to 250RPM, the MS with kick into normal running mode, but it could be too early. Mine is set to 400RPM. I had an issue on winter where my cranking RPM value got kicked down to 200 due to a firmware change. I had trouble getting the car to start and stay running...it would catch and stumble out. As soon as I changed the value back to 400RPM I never had the issue again.

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This confuses me. How does the MS know it's cranking before it's sync'd?
It should read the pulses instantly, but it skips pulses (user set) before it does anything, correct?
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Old 09-09-2011, 12:11 PM   #6
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I see your point, though if I had a weak battery I wonder if the cranking would ever reach 400rpm unless I opened the throttle a bit.

<edit> I think I may have misunderstood. I thought Cranking RPM was the speed at which the MS decided it was time to fire the ignition and start the engine, but that's wrong, isn't it? It's actually the speed at which it decides it has started the engine - the ignition's firing all the time fuel is being injected. Is that right?
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Old 09-09-2011, 12:18 PM   #7
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yes, because it would catch. The cranking RPM is the point where the motor isn't cranking, but actually running. It needs to be HIGHER than your actual RPM during cranking. 300RPM will work; I used that for years.
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Old 09-15-2011, 09:04 AM   #8
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Just a quick bump, as clean starting is still a bit hit and miss:

When the motor reaches Cranking RPM, is that when the MS stops adding the Cranking Pulse and starts the ASE Taper?
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Old 09-15-2011, 09:42 AM   #9
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Quote:
Originally Posted by Martin Y View Post
Just a quick bump, as clean starting is still a bit hit and miss:

When the motor reaches Cranking RPM, is that when the MS stops adding the Cranking Pulse and starts the ASE Taper?
Correct. Above the cranking RPM, the MS transitions from the cranking pulse table to the VE table, and begins applying ASE and WUE.
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Old 09-15-2011, 10:08 PM   #10
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I have a very similar problem with my DIYPNP. The MS does not deliver any fuel for .5 seconds after the it detects the cranking. Any idea why no fuel is delivered for the first .5 seconds.
Attached Thumbnails
Cranking RPM and the process of starting-ms_slow_start.jpg  

Last edited by John151; 09-15-2011 at 11:00 PM.
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Old 09-16-2011, 10:04 AM   #11
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Could we see the MSQ too?
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Old 09-17-2011, 10:42 AM   #12
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MSQ attached.
Attached Files
File Type: msq CurrentTune.msq (78.9 KB, 129 views)
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Old 09-17-2011, 02:28 PM   #13
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I have exactly the same behavior, 0.5 sec before fuel is injected. Been trying to get rid of it ever since I built the MS (2009). Think it's inherent to the software.
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Old 09-19-2011, 10:51 AM   #14
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bump
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Old 09-19-2011, 11:17 AM   #15
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You can try changing Skip Pulses from 3 to 1 if this is a concern.
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Old 09-19-2011, 12:09 PM   #16
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What's the purpose of the skipped pulses?
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Old 09-19-2011, 12:37 PM   #17
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The first couple of pulses might be unstable, given that the engine is still accelerating under the power of the starter motor, so the fuel/ignition delivery might not be optimal. Ideally, you want fuel and ignition to be delivered under stable conditions, ie the engine is spinning at a constant angular velocity.
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Old 09-20-2011, 01:44 AM   #18
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Quote:
Originally Posted by Matt Cramer View Post
You can try changing Skip Pulses from 3 to 1 if this is a concern.
This shaved off .1 second (delay now at .4 sec).

My battery voltage drops into the 9s while cranking. Would this be a factor?
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Old 09-24-2011, 01:24 AM   #19
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Connect a charger and see if that helps. If yes, then yes. I would say it will have a problem spinning the engine with that low of voltage.

Have a great day,
Jared
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Old 09-24-2011, 10:31 AM   #20
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that's where the voltage goes when cranking...
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