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Depressurize fuel system to change high pressure

rasmuss

New member
Hi Im planning to change the high pressure fuel filter on my BF75D. When I read my Seloc shop manual it says I first need to depressurize the high pressure side. In my owners manual I found a guide on draining the vapor separator. Will this depressurize the high pressure fuel system?
 
I'm pretty sure you'll find high pressure is not an issue when changing the high pressure filter. There is no high pressure unless the pump is running....
 
Going to somewhat disagree with Alan on this. If you have run the engine for any reason within a couple of hours of changing out the HP fuel filter, you should relieve any fuel pressure remaining in the system. Most FI Hondas have a fuel pressure relief bolt on top of or near the cover to the HP fuel filter. Carefully loosen it with a shop towel handy to absorb any fuel that may come out.

On another note - be careful with the Seloc or any other after-market shop manual - too many errors and omissions. Try to find the correct Helm shop manual for your Honda.
 
Going to somewhat disagree with Alan on this. If you have run the engine for any reason within a couple of hours of changing out the HP fuel filter, you should relieve any fuel pressure remaining in the system. Most FI Hondas have a fuel pressure relief bolt on top of or near the cover to the HP fuel filter. Carefully loosen it with a shop towel handy to absorb any fuel that may come out.

On another note - be careful with the Seloc or any other after-market shop manual - too many errors and omissions. Try to find the correct Helm shop manual for your Honda.

Not to argue, but for a better understanding. I'm pretty familiar with the 50D engine as I spent a LOT of time diagnosing one for an issue I was having. On that motor, the incoming fuel passage to this filter led directly to the outlet side of the pump - or that's how I remember it anyway. There's no check valve there that might prevent immediate bleed down when the pump is turned of. Nor is there a check valve in the pump. I'm assuming the 75 is no different.

What am I missing?
 
No argument here. I also made an assumption that the FI system for the 75 would be similar to the 150 to 250 Honda's.

Hopefully someone who knows the 75 well will pipe in.

But as I reread your observations on the 50, I started thinking about the fuel system on the bigger Honda's, specifically my 225. I have experienced residual pressure in the fuel system when I change the HP filter or mess around with the VST. I'm not sure why. I suspect that with the injectors shut down and the float valve in the VST closed, there is no place for the fuel to bleed out.
 
VST chamber is vented. It would not drain properly, nor would it be able to fill otherwise. My thought anyway.

Whatever. I suppose it's better to be safe that sorry. For out PO, putting a rag over your wrench while cracking that testing port would only take a second. If I remember, I'll circle back to this with a comment the next time I have one down. -Al
 
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Ok so, I should depressurize with the service bolt. I saw I need to get a new washer for it every time. I will be replacing the filter after a winter of storage. Should I still depressurize or is the pressure definitely gone by spring?
 
I'll likely get flamed for saying it, but that washer doesn't need to be replaced every time. Not in my experience anyway. Maybe replace it and the filter gasket every other time you replace the filter?
 
I don't replace the washer every time. Once you are finished, turn on the key switch to pressurize the system. Look for leaks around the bolt. If none, you are good to go. You should also pressurize the system after replacing the HP fuel filter. It's very easy to get that flimsy O ring misaligned. Don't ask me why I know that!

If the engine has sat for a period of time, it is unlikely that there will be any pressure in the fuel system unless you turn on the key switch before hand. That activates the HP fuel pump which pressurizes the system.
 
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