Author Topic: Breva 750 no start  (Read 250 times)

Offline breva750

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Breva 750 no start
« on: December 01, 2021, 03:40:45 PM »
Battery had been connected backwards, now cranks but no start.
Could be one of the relays?

Offline guzzisteve

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Re: Breva 750 no start
« Reply #1 on: December 01, 2021, 04:56:05 PM »
Most likely the ECU is toast M15RC, bout $600 if lucky or get a MyECU, it's the Cat's Meow but more $.
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Offline guzzisteve

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Re: Breva 750 no start
« Reply #2 on: December 01, 2021, 07:33:11 PM »
Battery had been connected backwards, now cranks but no start.
Could be one of the relays?

Here's one, if you remap it
It also has no O2 hook-up, if you got a laptop you could do it. Cheap too from a good guy-------

https://www.ebay.com/itm/324160372895?hash=item4b7976c09f:g:8NQAAOSwHoFetd-o&vxp=mtr

AND the correct one--------------------------

https://www.ebay.com/itm/334124755282?fits=Make%3AMoto+Guzzi&hash=item4dcb632952:g:9AkAAOSwn4ZcPp39&vxp=mtr
« Last Edit: December 01, 2021, 07:42:46 PM by guzzisteve »
"Pray through Carlo & your bike shall be healed"
Location: Planet Earth

Online Kiwi_Roy

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Re: Breva 750 no start
« Reply #3 on: December 01, 2021, 08:14:45 PM »
Putting the battery in backwards should not damage the ECU, it has a special polarized relay (11) to avoid that, it won't let the relay close and put power on terminal 26.
https://www.thisoldtractor.com/guzzi007/schematics/2004_750_Breva.gif
Its possible something let go but shouldn't be the ECU
Is the dash behaving normally.
Check the relay base's (11 & 12) for +12 Volts on pin 30
When you turn the bike on does the fuel pump prime (run for a couple of seconds)
What other symptoms do you have?

WORK IN PROGRESS
« Last Edit: December 01, 2021, 08:48:19 PM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Wildgoose Chase Moto Guzzi

Re: Breva 750 no start
« Reply #3 on: December 01, 2021, 08:14:45 PM »

Offline breva750

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Re: Breva 750 no start
« Reply #4 on: December 01, 2021, 09:00:39 PM »
Putting the battery in backwards should not damage the ECU, it has a special polarized relay (11) to avoid that, it won't let the relay close and put power on terminal 26.
https://www.thisoldtractor.com/guzzi007/schematics/2004_750_Breva.gif
Its possible something let go but shouldn't be the ECU
Is the dash behaving normally.
Check the relay base's (11 & 12) for +12 Volts on pin 30
When you turn the bike on does the fuel pump prime (run for a couple of seconds)
What other symptoms do you have?

WORK IN PROGRESS

Kiwi_Roy:

1. The dash behavior is normal
2. The fuel pump primes as evidenced by the smell of gas
3. No other abnormal symptoms noted

Will check the voltage on pin 30 for 12 volts asap

Thanks for the schematic and your knowledge!!

Offline jrt

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Re: Breva 750 no start
« Reply #5 on: December 01, 2021, 09:29:07 PM »
Then the ECU is ok.  Roy is the man!  He (and others) helped me with my Cali problems.

Maybe one of the relays, maybe the crank position sensor?  (I'm sensitive to that now!)
L-720
1973 Eldorado
2003 Yardbird (1100 hydro)

Online Kiwi_Roy

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Re: Breva 750 no start
« Reply #6 on: December 01, 2021, 10:01:15 PM »
Do you actually hear the pump running?
Why was the battery taken out in the first case? how long ago?
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921

Offline breva750

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Re: Breva 750 no start
« Reply #7 on: December 01, 2021, 11:11:51 PM »
Do you actually hear the pump running?
Why was the battery taken out in the first case? how long ago?

Yes, can hear fuel pump running.
Dead battery about 4 weeks ago.

Offline rodekyll

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Re: Breva 750 no start
« Reply #8 on: December 02, 2021, 02:06:27 AM »
I don't remember if this one has the tipover switch or not.  If yours does and it got dislodged while the battery was out it might be the problem.

Online Kiwi_Roy

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Re: Breva 750 no start
« Reply #9 on: December 02, 2021, 10:04:58 AM »
Yes, can hear fuel pump running. Thats good, the ECU processor must be running
Dead battery about 4 weeks ago.
I don't remember if this one has the tipover switch or not.  If yours does and it got dislodged while the battery was out it might be the problem.
Yes good one David, according to the diagram it has the Bank Angle Sensor (42) connected to the ECU, I think the contacts of the sensor need to be closed.
https://www.thisoldtractor.com/guzzi007/schematics/2004_750_Breva.gif
The next thing I want to know is. Does the pump run while the bike is cranking over? The way to tell this is connect a small 12 Volt lamp to the Red wire that powers up the coils, injectors and fuel pump. The easiest way to do this might be wrap a small wire around the 87 pin of the Secondary Injection relay (12), run it to one side of the lamp. The other side of the lamp goes to chassis.
This lamp will light when the key is turned on while the pump primes (based on a timer in the ECU) and it should light again while the bike is cranking over triggered by pulses from the Crank Position Sensor (2) (you won't be able to hear the pump over the racket the starter makes)
If the red wire is not alive you don't have power to the coils or injectors and the bike will never start.
You haven't had the sensor off have you? some owners pull them off and stick an "O" ring or extra gasket on to fix the oil leak and wonder why the bike won't start. The sensor is a coil of fine wire wound over a magnet.
As the gear spins under the magnet it causes ripples in the magnetic field which are picked up by the coil and sent to the ECU as a low Voltage sine wave. The ECU recognizes the motor is turning over and grounds the coil of the Secondary Injection relay turning it On to power up the fuel and spark.
You can check the sensor with an Ohmmeter, it should measure about 680 Ohms the sensor has a plug about 18" away, should be easy to find, just trace the cable.
« Last Edit: December 02, 2021, 02:58:54 PM by Kiwi_Roy »
72 Eldorado
17 V7iii Special
76 Convert

Moto Guzzi - making electricians out of riders since March 15 1921


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