Cranking RPM and the process of starting
09-09-2011, 09:36 AM
#1
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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?)
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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09-09-2011, 09:37 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.
the delay is the MS confirming the crank inputs and syncing.
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09-09-2011, 10:55 AM
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It should read the pulses instantly, but it skips pulses (user set) before it does anything, correct?
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09-09-2011, 11:11 AM
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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?
<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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09-09-2011, 11:18 AM
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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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09-15-2011, 09:08 PM
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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.
Last edited by John151; 09-15-2011 at 10:00 PM.
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09-19-2011, 11:37 AM
#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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