Cold Start stalling

[Dafeimao85]

Hi All, need your expert opinion. I always have a problem starting the bike when it is cold recently. Gen 2 Busa L6 ABS with 70k mileage

Staying in Singapore, temperature is always 34 DegC day ~ 28 DegC night.

Sequence of event will always be

1) Bike start rpm goes to 1500rpm for 10sec to 15sec
2) rpm drop slowly sputter and died off
3) re crank few tries and rpm goes to 1000 rpm for 1 sec and stall

To start the bike I needed to re crank and turn throttle to start the bike and maintain rpm 2k til temperature raise just a little bit.
Once the temperature reading raise. I switch off the engine or using kill switch, I can instant start the engine regardless of number of retry.

Conclusions I had: the engine unable to start in cold which make me suspect is the auto choke or ISC valve problem.

BUT! There are times successfully started without issue but with the clutch in all the way til bike is warm up.

As it's not always successful start with clutch in. It make me wonder it's the idle valve problem or clutch problem.

Thanks for all the input!

 

[sixpack577]

It is not the clutch.
A clutch problem would not go away after the bike warms up either.
Have you checked for any codes?
Does the FI light come on or stay on when it cold starts or before it stalls?

 

[Dafeimao85]

It is not the clutch.
A clutch problem would not go away after the bike warms up either.
Have you checked for any codes?
Does the FI light come on or stay on when it cold starts or before it stalls?

Hi Sixpack577,

FI did light up once and go away and shortly this problem started

Check the obd2. Did get throttle body fault but did not give any C## code.

Mechanic proceed to reset as it was difficult to tell if the code was a old alarm uncleared or the actual alarm. However til date we did not see anymore throttle body error alarm anymore but problem persist.

For the clutch part I agree with you that it shouldn't go away even with the engine warm up.

That's why I am thinking the next step is to service the ISC Valve. If still can't fix the problem, then I will replace it and rewrite the ecu as per service manual.

 

[sixpack577]

The ecu will not store codes.
You can jump the red/white to black/white and leave it, then crank it.
See if it momentarily flashes a 2 digit number after the 'C' other than 00.

 

[Dafeimao85]

The ecu will not store codes.
You can jump the red/white to black/white and leave it, then crank it.
See if it momentarily flashes a 2 digit number after the 'C' other than 00.

Hi bro, thanks for the solution but sorry I don't really understand the jump connection.

Do you mean to jump a cable at the obd port? Then look at the speedo for C## code? Or do I jump the cable and force in the obd connection so that I can read the C## from the obd reader? Or the jump cable on other equipment?

Thanks for the patient to explain and help.

 

[sixpack577]

Hi bro, thanks for the solution but sorry I don't really understand the jump connection.

Do you mean to jump a cable at the obd port? Then look at the speedo for C## code? Or do I jump the cable and force in the obd connection so that I can read the C## from the obd reader? Or the jump cable on other equipment?

Thanks for the patient to explain and help.

No obd2 scanner needed.
Use a wire to connect red/white to black/white in the white plug under the seat, that will bring up the C00 on the dash.
Leave the wire in, and leave the C00 on the dash.
Cold start the bike, if any codes are present the 00 will change to another 2 digit number that will reference a code.

 

[Dafeimao85]

No obd2 scanner needed.
Use a wire to connect red/white to black/white in the white plug under the seat, that will bring up the C00 on the dash.
Leave the wire in, and leave the C00 on the dash.
Cold start the bike, if any codes are present the 00 will change to another 2 digit number that will reference a code.

Hi bro! Ur method works! Able to bring up the C00 on the speedo dash. Learn something new!

Alas the bike still stall on cold start. The C00 remains unchanged.

This test makes me conclude more on the ISC Valve. I am suspecting the ISC valve unable to full close to choke the air hence the cold stall. As the valve is not electrically fryed, hence it still can send signal back to ecu resulting C00 error code unchanged.

 

[Kiwi Rider]

I wonder if the coolant temp sensor has failed and producing incorrect data to the ECU… I’ve seen this on cars occasionally and when cold the ECU thinks the engine is warm so the fueling provided is way too lean, and engine won’t run properly.
It’s uncommon for a CT sensor to fail, but it’s worth looking at and testing.

 

[Dafeimao85]

I wonder if the coolant temp sensor has failed and producing incorrect data to the ECU… I’ve seen this on cars occasionally and when cold the ECU thinks the engine is warm so the fueling provided is way too lean, and engine won’t run properly.
It’s uncommon for a CT sensor to fail, but it’s worth looking at and testing.

Hi Kiwi Rider,

I have thought about it too. But if the coolant temp has fail, the speedo coolant temp that takes reading from the same sensor should fail instead of reacting normally?

The other possibilities are air intake temp sensor which I did use obd reader and get almost identical environment temperature.

I intend to do this over the next weekend.

1)Remove ISC valve from throttle body
2) clean up the Isc valve
3) applied 12V to the isc valve to see if it open and close fully.
4) using stringe, tubes and tapes to create a vacuum for the vacuum tube to check for leaks.
5) fix back and try start again.