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post #1 of 12 (permalink) Old 10-17-2019, 02:02 AM Thread Starter
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Thumbs down Loud noise: Fuel Injectors sound like they're pumping air?

2015 Thruxton EFI 900.

This only seems to happen at a stop in neutral. The injectors sound like they run out of fuel and are suddenly pumping air? It gets very loud in bursts (it sounds like a water pump when it's pumping no water vs when water is flowing through it) goes on, off, on, off, on, off.

I found that using the idle rpm adjuster knob to raise the idle rpm fixes it, but now it idles quiet high.

Any ideas what this could be?
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post #2 of 12 (permalink) Old 10-17-2019, 01:38 PM
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Check all your rubber connections and fuel lines. They could be either loose or rotting away.
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post #3 of 12 (permalink) Old 10-17-2019, 03:02 PM
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So assuming it is the sound heard after having the high pressure fuel line off the tank when powering up first time after reconnecting it, then yes that is what air purging sounds like. Why it's happening could be a few different things. First check carefully for any signs of fuel leakage along the fuel line from tank to injectors.
because it's happening at low rpm might be electrically induced as volts drop off. How is you battery condition? Put a multimeter across terminals while idling at rpm that causes sound to see if volts are on low side. Should be close to12.5 or more. Thinking is maybe pump not getting enough power to keep pressure up at injectors.
Could be a fuel pump or fuel filter issue. Not sure how pressure is regulated on these bikes. Might need to open up the pump fixture underside of tank to start replying filter and seals.
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post #4 of 12 (permalink) Old 10-17-2019, 10:40 PM
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Have you modified or removed/disabled the Secondary Air Injection (SAI)?
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post #5 of 12 (permalink) Old 10-18-2019, 01:28 AM Thread Starter
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Thanks for the help guys. I just bought the bike so haven't done a proper tear down and inspection yet. Upon second ride the noise may actually be the fuel pump - I can't tell yet as I can't run the bike with the kickstand down (neutral switch not working)

@Tornado99 it does seem to be electronically induced as i can hear a switch clicking when it turns off, but my battery is good - it's 13v+

I'll have a proper check this weekend but this is a good place to start. Thanks guys!
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post #6 of 12 (permalink) Old 10-18-2019, 01:29 AM Thread Starter
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Originally Posted by wenzel850 View Post
Check all your rubber connections and fuel lines. They could be either loose or rotting away.
I'll have a look this weekend but it's a 2015. Things seem pretty well maintained - especially areas away from weather like under the tank but I'll check anyway!
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post #7 of 12 (permalink) Old 10-18-2019, 01:30 AM Thread Starter
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Have you modified or removed/disabled the Secondary Air Injection (SAI)?
I'll look into it - the airbox has been removed and velocity stacks installed (I'm waiting for some pod filters to come in). How would removing SAI affect this?
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post #8 of 12 (permalink) Old 10-18-2019, 02:25 AM
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The click you are hearing may be the SAI solenoid opening and closing around idle speed. Quite annoying really. You can tell if SAI still installed by looking for the big stainless pipes the the outside of each of the spark plugs (making them a right pain in the arse to get out & in).

Fuel pump whine when purging air is very loud and as I said, it's common to hear it after pulling fuel line and re-connecting when you first turn ign key to run position and the clocks cycle. If that's what you hear while idling it is very odd indeed. I'd check the fuel connection is correctly seated...there is a goofy snap clip that needs to engage over the coupling. But I'd think if that were not done right you'd have a lot of fuel spraying out from under the tank...
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post #9 of 12 (permalink) Old 10-18-2019, 06:56 PM Thread Starter
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The click you are hearing may be the SAI solenoid opening and closing around idle speed. Quite annoying really. You can tell if SAI still installed by looking for the big stainless pipes the the outside of each of the spark plugs (making them a right pain in the arse to get out & in).

Fuel pump whine when purging air is very loud and as I said, it's common to hear it after pulling fuel line and re-connecting when you first turn ign key to run position and the clocks cycle. If that's what you hear while idling it is very odd indeed. I'd check the fuel connection is correctly seated...there is a goofy snap clip that needs to engage over the coupling. But I'd think if that were not done right you'd have a lot of fuel spraying out from under the tank...
Finally got a chance to take her apart. SOOOOO.... the previous owner did a bodge job with the Airbox removal. The whole SAI system is still intact but not connected to anything so there's an open intake on the pump. That's why i can hear it so loudly and it sounded like it was coming from the fuel pump area!

I guess i'll have to get the proper bungs to plug it up and then just remove the whole system. Wondering if you can still hear the pump that loudly if the pump is left there to avoid Check Engine light?
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post #10 of 12 (permalink) Old 10-18-2019, 08:06 PM
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Quote:
Originally Posted by Pangerz View Post
Finally got a chance to take her apart. SOOOOO.... the previous owner did a bodge job with the Airbox removal. The whole SAI system is still intact but not connected to anything so there's an open intake on the pump. That's why i can hear it so loudly and it sounded like it was coming from the fuel pump area!

I guess i'll have to get the proper bungs to plug it up and then just remove the whole system. Wondering if you can still hear the pump that loudly if the pump is left there to avoid Check Engine light?
Great news...no spendy fuel pump replacing for you.

One SAI defeat method is to just disconnect the air hose from air box and fit a marble tightly into the hose then plug the airbox hole. Leaving the solenoid and it's electrical connection all in place...so it will merrily click away thinking it is still letting air into the exhaust stream. No codes will be thrwon as the ECU can't tell any differently. If you go the whole hog (much better IMHO) and remove the solenoid and it's associated plumbing, then you either need to wire in a resistor (value?) to the electrical connection to fool the ECU or you download TuneECU freely and buy the $20 OBDII cable for the bike and disable the warning light. The cable and app are well worht it as they let you do so many other useful things on the bike like balancing throttle bodies, reading fault codes, swapping in new maps (something you will be needing to do on the modified airbox setup).

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