Cam signal characteristics / won't run sequentially

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Dennis_Zx7r
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Cam signal characteristics / won't run sequentially

Post by Dennis_Zx7r »

I can't get the engine to run when a cam signal is fed to my MS3X. It cranks, but doesn't start.
I use a microprocessor to generate a cam signal based on the MAP signal of cylinder #1. Digital output (5V pulse) is then sent to the CamInput pin. So it may well be the signal is not what the MS expects.

Log of the engine running attached. Started without Cam signal connected, connected it after the engine ran for about 15 seconds.
Also, a log of the engine cranking with the Cam signal connected.

Am I missing something obvious, or what should I test for?
My project: Link
grom_e30
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Re: Cam signal characteristics / won't run sequentially

Post by grom_e30 »

cam signal happens in the crank missing gap, thats the only place it can't happen. try using the opposite edge of the signal switch from second trigger active on rising to falling or visa versa.
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
Dennis_Zx7r
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Re: Cam signal characteristics / won't run sequentially

Post by Dennis_Zx7r »

Nice, thanks. Hoped something like that would be the case.
I'm completely free in shifting the signal. I guess right in the middle of two missing gaps may be best then?
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jsmcortina
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Re: Cam signal characteristics / won't run sequentially

Post by jsmcortina »

Dennis_Zx7r wrote:Nice, thanks. Hoped something like that would be the case.
I'm completely free in shifting the signal. I guess right in the middle of two missing gaps may be best then?
That should be fine.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

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Dennis_Zx7r
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Re: Cam signal characteristics / won't run sequentially

Post by Dennis_Zx7r »

Well I changed the trigger and it seems to work just fine, and already seems to be well positioned. Thanks!
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grom_e30
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Re: Cam signal characteristics / won't run sequentially

Post by grom_e30 »

are you using a single edge to trigger it? as opposed to poll level?
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
Dennis_Zx7r
Experienced MS/Extra'er
Posts: 374
Joined: Thu May 26, 2016 1:25 pm
Location: Germany

Re: Cam signal characteristics / won't run sequentially

Post by Dennis_Zx7r »

Previously used falling edge as the downward slope is steeper and therefore should be more reliable. Now using rising edge. Tried it multiple times and worked every time, so I'll leave at that for the near future... so much other stuff to do right now and have to verify if this works on altitude anyway. Think it will though, as I base the trigger thresholds in the microcontroller on a baro% value instead of a fixed pressure/adc value.

Picture of MAP during cranking in case you're interested. It's a 115kpa sensor, lowest data point at 2V indicates around 55kpa, 4V around 100kpa.
Image
My project: Link
grom_e30
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Re: Cam signal characteristics / won't run sequentially

Post by grom_e30 »

yeah the map reading looks quite repeatable nice work
1990 bmw 320i daily driver with m20b25 ms3 sequential fuel, 380cc injectors, d585 coil near plug, home made cam sync, launch control, fan control, vss, homebrew egt logging what's next????
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