Annoying EFI air purge - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 9 (permalink) Old 05-12-2017, 06:43 PM Thread Starter
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Annoying EFI air purge

My 2012 has had an annoying air purge squeal at key turn when the tank is not full. There is no apparent impact on performance, but it needs to go. Grassyass for any ideas!
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post #2 of 9 (permalink) Old 05-12-2017, 08:55 PM
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Gotta describe what you mean by air purge. It is coming from the gas tank cap? There is a tank vent/overflow hose line underneath the tank....it just slips on/off easily for when you are R&R'ing the tank.
The far end of the hose is down under the left foot peg/frame rail someplace...there have been reports of these plugging up with grime and leading to poor running as the tank starts to evacuate.

Also, have you changed the tank cap? I believe there is some kind of vent built into the stock one. Your might be failed if still original.

Also, does your bike have the added "California" emissions equipment? There is some kind of additional plumbing to a charcoal canister...I think on cars, these accumulate fuel vapour when engine is off and purge to air intake when running so the vapours get burned and not released to the atmosphere. Not sure how it works on these bikes though...mine does not have it.

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post #3 of 9 (permalink) Old 05-12-2017, 11:08 PM
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Are you talking about the fuel pump priming (and/or purging air from the system) in the tank when the key is turned on?

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post #4 of 9 (permalink) Old 05-12-2017, 11:34 PM
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The OP probably means the squealing sound you sometimes get when the fuel pump primes. That noise comes from the fuel pressure regulator inside the tank and it's caused by the system expelling air from the fuel pipes and fuel rail.

Unlike carbs, with their float chamber "reservoir", injection systems can't tolerate any air bubbles in them. Consider that the fuel has to be at 3bar (44psi) as it enters the injector fuel rail. An air bubble would cause erratic running as air, unlike fuel, is compressible. It cannot exit from the still-closed injectors, so has to go out further up the system, to the regulator, as this has a facility to vent excess fuel when the pressure exceeds the preset level. The same vent lets the air out into the tank.

It usually happens following dismantling of the fuel pipes or tank removal, and also after the bike has not been used for a long time.

If it happens everytime the bike is used the chances are that the one-way valve in the pump is leaking slightly or there's a small fuel leak at the hoses or quick-release fittings. It's of no consequence unless the noise is annoying.

In a few of the cases where this screeching occurs all the time some dealers have replaced the pressure regulator. Member Gina 1 successfully cured it by adding 3 or 4 oz of Marvel Mystery oil or 2 cycle premix oil to a full tank.
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post #5 of 9 (permalink) Old 05-15-2017, 05:20 PM
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Wait... you're saying that shouldn't happen every time I turn on my key? It always has, and I thought that was normal - annoying, but normal. Would I replace the pump then? Or is there a valve that could be replaced itself? Should it pump but not squeak? Or should it not need to pump?
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post #6 of 9 (permalink) Old 05-15-2017, 05:56 PM
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Quote:
Originally Posted by jasonmrop View Post
Wait... you're saying that shouldn't happen every time I turn on my key? It always has, and I thought that was normal - annoying, but normal. Would I replace the pump then? Or is there a valve that could be replaced itself? Should it pump but not squeak? Or should it not need to pump?
The pump should run for a few seconds when first turning key to run position then stop, it should sound like an electric motor turning , think battery drill noise , once hitting start button pump is continually running but can't hear due to engine noise being louder

If you've had the tank off the noise is like it is turning while dry so a louder higher pitched noise but once fuel flowing through should be the normal quieter noise

Don't know if that helps you any or not
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post #7 of 9 (permalink) Old 05-16-2017, 07:53 AM
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I get the squeak every time the bike is cold, so it sounds like I need a better seal somewhere between the pump and the throttle bodies? I don't get any visible fuel leak, but I would think that gravity would keep things pretty well primed unless it is leaking out somewhere. Where's the check valve that goes bad sometimes?
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post #8 of 9 (permalink) Old 05-16-2017, 09:31 AM Thread Starter
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It definitely sounds like the EFI must pump the air out every time the tank is less than 1/2 full. Can't imagine this leak down is normal. Other EFI bikes I have/have had did not do this?
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post #9 of 9 (permalink) Old 05-16-2017, 09:58 AM
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Quote:
Originally Posted by jasonmrop View Post
I would think that gravity would keep things pretty well primed unless it is leaking out somewhere. Where's the check valve that goes bad sometimes?
I don't think gravity comes into it. The system has to be pressurised by the pump (46 psi). The quick release fittings are sealed by O rings and could have a slight leak that would go unnoticed as it would evaporate very quickly in the under-tank heat.

On these immersed fuel pumps there's usually a one-way valve at their outlet. Layout of components inside tank, note also the regulator that some dealers have changed to cure the problem (£45):

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