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Discussion Starter #1
No prime from fuel pump when I turn the key to the Run position. (I don't remember: Is it supposed to prime every time I turn the key to the Run position?) With spark tester on #4, I get one blip of spark every 10 or 15 crank revolutions if at all. Do you think I'm looking at an SPU problem? I have the original blue backed SPU. I've removed the tank, connected 12V to the pump wires and the pump runs. Removed the pump, no broken or disconnected hoses. Probed the pins in the connector to the pump and the bike is not sending voltage to the fuel pump.

Here's the story... It died once on the freeway the other day. I restarted and rode 20 miles home with no further problems. Next morning, cranks, but no start. Put the battery on a charger because I cranked it until the battery sounded weak. Hooked up a spark tester to #4. Initially, I was getting spark, but it seemed like it was pulsing maybe every other revolution instead of 1x every revolution. Fuel wasn't priming every time I turned the key to Run. If I waited a minute or so in between tries, it would prime. Today, I continued diagnosing and we're at the first paragraph; rarely any spark at all, never any prime.

BTW, I can't change my email address. I click Save Changes and nothing happens. Nothing is working right. I'm just going to lie down and stop breathing.
 

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@moocowman: again, I implore you....and everyone else...to put your bike model and year in your signature line. How can we help if we don't have this basic information?
 

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Yes, the pump should prime EVERY time.

1.jpg

2.jpg

From the above diagrams you can see the components needed to start the bike. The fuses and relays are contained in the SPU and can certainly be suspect.

Another culprit is battery capacity, quality and condition. The ECU has a voltage cutout that will cease operation of the ECU when low voltage is sensed. This will prevent the bike system from functioning if, say during the high load of the starting sequence, voltage dips below that value.

Load test your battery.

FWIW: There are many differences between the wiring diagrams and components in the 2005/6 B4 910R/S and the later models. I'm not just being cheeky.
 

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Discussion Starter #6
I load tested the battery after I took it off the charger. Then, I charged it again before I ran the tests. I just checked again and now the pump primes when I turn the key to Run! But if I try to repeat it within 45 second or so, it doesn't prime. Have to wait before it primes again. Maybe that's normal? Like, maybe you can't do it in quick succession. Either way, I'm still not getting spark.

Is it correct to say if I'm getting voltage to fuse 15, the relay is working properly? The fuse is after the relay. So, if that checks out ok, what's missing is the ground pulse from SPU to the injectors and ignition coils. And if there's no pulse, the problem would be SPU or whatever tells the SPU to send a pulse, which would be crank sensor, correct?
 

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Your analysis is sound with one exception: The SPU is the Service Power Unit, it provides power distribution to the bike.

The ECU, Electronics Control Unit, provides the signal to the injectors after seeing a pulse form the crank position sensor pick up.
 

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Perhaps you are looking in the wrong areas.

I believe your relays are INSIDE the SPU....
 

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A couple of years ago, I'd tackle a task like stripping down the SPU; might even enjoy it. But I just don't have the time and patience anymore. I guess I'll be ordering an SPU. You're sure that relay is in the SPU, right?
 

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Are you going to blame this on me if you can't read the manual's electrical diagram or use ADVANCED SEARCH?

To the best of my knowledge, the relays are contained in the SPU.

Disclaimer: I do not own a bike with an SPU. All of my knowledge is derived from reading things at a 6th grade level...and comprehending at a Doctorate Level.
 

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Discussion Starter #15
Whoa, wait a minute. Cool off, man. I'm not blaming anything on you. You seem more knowledgeable than me on the inner workings of this bike. So I asked for clarification because you said you "believe" they're in the SPU. I don't see anywhere in that electrical diagram that indicates the relays are in the SPU. If you're going to get pissy and short with people, don't offer your "help".
 

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Discussion Starter #16
And BTW, I did search for "power relay" in the B4 forums and found no threads that specifically discussed the power relay being located in the SPU. Although, I don't have time to scan each of the hundreds of posts that include the words "power" and "relay". Maybe I'm missing some special type of search you know of that I don't, as I don't spend a good chunk of my life exploring these forums.
 

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I say "I believe" because I have not held an SPU in my hand.

You appear to be looking for certainty. You have the same information that I have.

You state that you cannot find the relays anywhere else.

1.jpg



Were it me, I'd replace the SPU.
 

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FWIW, you haven;t seen me "pissy"....yet.:smoking:
 

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And BTW, I did search for "power relay" in the B4 forums and found no threads that specifically discussed the power relay being located in the SPU. Although, I don't have time to scan each of the hundreds of posts that include the words "power" and "relay". Maybe I'm missing some special type of search you know of that I don't, as I don't spend a good chunk of my life exploring these forums.
There is no special type of search, but you do have to combine some intuition with some experience when searching for the unknown.

Aside from the previously listed thread, I'll assume you haven't had time to read this sticky thread at the top of the B4 forum, so here it is because I am fairly certain (I believe) you probably didn't read it:

https://www.mvagusta.net/forum/13-brutale-b4/41943-absolute-final-should-made-sticky-spu-cdi-thread.html
 

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With the exception of the starter relay (solenoid) all relays on the earlier Brutales are in the SPU.
 
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