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Tye

M50 PNP Ecu usb connection lost during cranking

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Hi everyone,

i noticed that during cranking, the USB connection between my ECU and laptop is lost. It reconnects in a couple seconds if I have Auto connect on. Just curious why this happens. Is the USB connection somehow wired into the unloader relay circuit?

Not a huge deal, but it’s a little annoying trying to log cranking and post start parameters.

I have an M50 in my e30 running a G4+ PNP. 

 

Thanks

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Chances are the supply voltage is dropping low enough to cause the disconnect. You could check this by using the internal ECU logging to see if ECU stays live.

The other can be noise off the starter causing coms issues and windows dropping the connection. 

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I have the same problem with my S52 discussed in this thread: 

My issue was voltage dropping too low during starting. One thing that may help is powering the ecu and engine electronics directly from the battery instead of the starter terminal. That way it is not subject to the voltage drop of the starter power cable during cranking. 

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On 10/29/2019 at 4:11 PM, Simon said:

Chances are the supply voltage is dropping low enough to cause the disconnect. You could check this by using the internal ECU logging to see if ECU stays live.

The other can be noise off the starter causing coms issues and windows dropping the connection. 

Based on this ECU log, I don't see any voltage drops before the engine has started. However, I cant display a cranking area on the log. The very begining of the log is me turning on the ignition and waiting a few seconds for my Computer to connect to the ECU.

It looks like my car starts up instantly on this log, but it actually cranks for about 2 seconds before starting up every time.

The main reason i'm trying to fix this communication problem  is so I can figure out why this thing takes so long to start up.

As soon as the ECU syncs the triggers, it starts up instantly. What i'm really trying to figure out is if my long cranking issue is caused by the Triggers not syncing right away or maybe my ECU is losing power for a moment.

 

My main relay gets power directly from the battery in the trunk with a seperate wire. Not on the starter post.

long trigger sync log.llg

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On 11/3/2019 at 5:52 PM, Simon said:

Is the logging set to log all the time or is it activated off RPM?

Logging was set to full time for this log.

My car consistently takes this long to start.

 

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It is not a USB comms problem, your ECU log stops and restarts after the engine starts, that means the ECU is switching off.  This could be caused by two main circuits.  As a quick test to eliminate where the problem is, can you try grounding pin 27 with a little alligator clip lead or similar and see if the ECU still drops out when cranking with that pin grounded.

W58bT9B.png

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Hi Adam,

So I tried grounding the main relay manually and I got the ecu to stay connected during cranking. If there is a permanent wiring solution to fix this, that would be great.

 

Still curious why the ECU takes so long to sync the triggers. Based on this log, I noticed that fueling doesn't start until the ecu sees RPM. As soon as fueling starts, the car starts instantly.

Is there any way to reprogram the ECU to start fueling as soon as a signal from Trigger 1 is present?

I would love to get a quick, OEM like startup from my car, much like the stock ECU.

Thanks for all of your help everyone!

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9 hours ago, Tye said:

So I tried grounding the main relay manually and I got the ecu to stay connected during cranking. If there is a permanent wiring solution to fix this, that would be great.

Ok, that suggests that it is the Mosfet that controls the main relay that is dropping out.  I remember a couple of years ago there was a small batch of Mosfets that were found to be outside of the their tolerance range so they would drop out at about 8.0V instead of the designed 6.5V.   One last check you could do is measure voltage between pin 55&56 try to see what it drops to when cranking.  If it drops below about 9V I would say it is an issue with your wiring or a ground somewhere, if it stays above about 10V then I would lean towards you possibly having one of the bad FETs.

 

9 hours ago, Tye said:

Still curious why the ECU takes so long to sync the triggers. Based on this log, I noticed that fueling doesn't start until the ecu sees RPM. As soon as fueling starts, the car starts instantly.

The M50 uses a "Cam Level" type sync which it generally very quick sync, the engine only needs to turn a maximum of 360deg before it will sync (often a lot less - basically as soon as it sees the missing tooth on the crank it is synced).  The pre-crank prime will dump fuel in before the engine is even turning.  So your slow start is probably just a setting or tune issue.  Attach a log of a start up and your tune so we can take a look.

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9 hours ago, Adamw said:

Ok, that suggests that it is the Mosfet that controls the main relay that is dropping out.  I remember a couple of years ago there was a small batch of Mosfets that were found to be outside of the their tolerance range so they would drop out at about 8.0V instead of the designed 6.5V.   One last check you could do is measure voltage between pin 55&56 try to see what it drops to when cranking.  If it drops below about 9V I would say it is an issue with your wiring or a ground somewhere, if it stays above about 10V then I would lean towards you possibly having one of the bad FETs.

 

Ok. Ill try this and report back.

 

9 hours ago, Adamw said:

The M50 uses a "Cam Level" type sync which it generally very quick sync, the engine only needs to turn a maximum of 360deg before it will sync (often a lot less - basically as soon as it sees the missing tooth on the crank it is synced).  The pre-crank prime will dump fuel in before the engine is even turning.  So your slow start is probably just a setting or tune issue.  Attach a log of a start up and your tune so we can take a look.

This makes sense. It still seems to take longer than it should. One last question, do these ECUs supply spark before syncronization? If so, the pre-crank prime settings should help me get a quicker startup. I haven't had much sucess using pre crank prime and getting a smooth startup so I turned it off.

Long crank main relay manually triggered..llg M52 NA 4 door Daily.pclr

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Your log show cranking starts at 4.306 seconds and the engine is running at 800RPM by 5.31seconds.  That is exactly1.0 seconds to start,  doesnt seem too excessive to me?  Is this as bad as it gets?

Can you attach a triggerscope of it cranking (turn ignition off so it doesnt start), I will see if there is anything that can be improved there.

 

14 hours ago, Tye said:

One last question, do these ECUs supply spark before syncronization?

No ecu can - how would it know which spark plug to fire and where TDC is if it hasnt synced.

 

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On 11/10/2019 at 11:29 PM, Adamw said:

Ok, that suggests that it is the Mosfet that controls the main relay that is dropping out.  I remember a couple of years ago there was a small batch of Mosfets that were found to be outside of the their tolerance range so they would drop out at about 8.0V instead of the designed 6.5V.   One last check you could do is measure voltage between pin 55&56 try to see what it drops to when cranking.  If it drops below about 9V I would say it is an issue with your wiring or a ground somewhere, if it stays above about 10V then I would lean towards you possibly having one of the bad FETs.

So I checked the voltage between pin 55&56 and I saw the voltage dropping to around 9.5volts initially, then jump up to 10+ volts. I tried 2 different multi-meters and they both registered pretty slowly. The voltage could be dropping alot lower for a instance, causing the MOSFET to drop out. All of my grounds are super solid. Is there any easy way for me to test the MOSFET in the ECU without breaking open the ECU? Or would i have to send in my ECU to get checked.

 

Heres a trigger scope.

 

m50 trigger scope.jpg

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Ok, triggerscope shows your arming thresholds are set pretty well, it should sync pretty quickly ( 1 crank turn max) with that.

 

5 hours ago, Tye said:

I checked the voltage between pin 55&56 and I saw the voltage dropping to around 9.5volts initially, then jump up to 10+ volts.

That sounds a bit marginal to me.  Most multimeters have quite a bit of averaging/filtering so you wont see relatively short spikes.  It is possibly dropping lower than 9.5V.  With your temporary ground on pin 27 so it doesnt drop out, you could set up ECU logging to run all the time and set it to log batt voltage at say 50Hz.  Turn off ign or fuel so you can log it cranking for say a good 5 seconds and that should give us a good idea what the voltage really drops to during cranking.

Is the power system stock in this car - battery hasnt been moved to the trunk or something?

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