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Old 14-09-21, 09:57 PM   #1
fwazathoth
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Default Fuel pump low voltage

Hi all,

I've had a problem for the last 6 months of my SV650S k3 not priming (fuel pump not whirring) and the fuel pump relay rapidly clicking (sounded like a continuous sound like hard drives read/writing).

I've had battery changed some bits rewired. More recently the garage checked the fuel pump resistance and found it was 1.3Ohms which I hear is low. A new fuel pump assembly costs a ridiculous amount so I've bought just the pump with the intent of taking the assembly apart and changing the pump over.

Will solve the problem? Why would a low resistance on the pump cause the relay to click at the rapid rate it was?
Thanks for any replies
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Old 15-09-21, 07:01 AM   #2
garynortheast
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Default Re: Fuel pump low voltage

Morning and welcome to the Org. Can't help on the fuel pump issue but there are a number of folks here who are much more electronically competent than me, and who will be along to help at some stage.
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Old 15-09-21, 11:44 AM   #3
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Default Re: Fuel pump low voltage

If the fuel pump relay was clicking, that would point to a problem with the power/signal it was receiving.

Is the new battery installed the correct power (CCA) for the bike?
Is 12V being received at the relay?
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Old 15-09-21, 12:29 PM   #4
fwazathoth
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Default Re: Fuel pump low voltage

There's around 10.5V at the relay. I realise this is a bit lower than you'd expect. Is the fuel pump resistance likely to be related or is that just a separate problem?
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Old 15-09-21, 12:56 PM   #5
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Default Re: Fuel pump low voltage

I was browsing the US forum and, coincidentally, stumbled on this from their resident electrical guru (TeeRiver) regarding the fuel pump relay.

- R/W (Fuel pump power IN to relay) Should have 12v at all times, even with the key off.
- O/W (Relay coil power) Should be 0v with key-off, 12v with key-on and kill-switch set to RUN.
- Y/B (Fuel pump relay control) Controls the fuel pump relay, comes from the ECM. This signal is ACTIVE-LOW which means ON= 0v, OFF=12v. This signal goes LOW for the 1st three seconds after key-ON, then pops up to 12v. Do not let Y/B come in direct contact with solid 12v at any time else the ECM can be damaged!
- Y/R (Fuel pump power) This is switched power OUT from the relay to the fuel pump. If R/W = 12, O/W = 12v, and Y/B = 0v then Y/R =12 and the fuel pump will run.
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Old 15-09-21, 02:30 PM   #6
DJ123
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Default Re: Fuel pump low voltage

Quote:
Originally Posted by fwazathoth View Post
There's around 10.5V at the relay. I realise this is a bit lower than you'd expect. Is the fuel pump resistance likely to be related or is that just a separate problem?
I would get the power to the relay sorted first, before moving onto the fuel pump.
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Old 17-09-21, 06:10 PM   #7
fwazathoth
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Default Re: Fuel pump low voltage

Hi, thanks for all the replies and sorry for not replying earlier. At the time of the replies I'd already taken the tank off and ordered a new fuel pump so thought I'd get that done first.
the filter was a bit grubby so I've changed it but the pump itself had 3Ohms of resistance so I left it in. I don't really understand why the unit as a whole has a lower resistance of 1.3Ohms.
Anyway, I but it back together and it's running now (though it does this and then stops at inconvenient times).
The relay seems to have correct voltage readings except for the 10.6V at the O/W wire where it should have 12V when priming.
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Old 17-09-21, 08:59 PM   #8
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Default Re: Fuel pump low voltage

If it plays up again could you run a lead straight from the battery to see if that sorts it (with an in line fuse?)
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Old 18-09-21, 06:48 PM   #9
fwazathoth
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Default Re: Fuel pump low voltage

From battery negative to the O/W? I'll give this a go if it pops up. Would you discourage trying this without an inline fuse as I may not have one atm?
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Old Yesterday, 03:58 PM   #10
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Default Re: Fuel pump low voltage

An online fuse is a good safety net - failing that check if the wires start to get warm/hot.
Once burnt out a wiring harness after fitting a fog lamp (long time ago) It shorted out somewhere and the harness just melted!
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