500 EFI won’t build fuel pressure
 

Have an 03 Cigarett with 500 efi’s, 568 hours on boat but fresh motors. I started losing some rpm and could start hearing brackfire out of the exhaust above 3k or so. Engine would start, idle, and cruise up to around 3k with no issues. Noticed fuel pressure gauge was only at around 18 lbs? Checked all plugs and no fouling or wet plugs, all looked good. Other engine is right at 40 psi. I replaced the cool fuel elec fuel pump and regulator, made no change on fuel gauge whatsoever? Where else can I look? Any advice would be appreciated. Mike

Check for collapsed fuel supply lines, dirty/clogged fuel filter, or clogged fuel tank vent.

look for a restriction.sounds like line from tank to pump could be collapsing and pull anti siphon valve at tank and see if its clogged up at all.

It shouldn’t start/idle/and run up to 3k like normal with only 18psi. I’d use a mechanical gauge to test fuel psi.

Or is fuel psi normal till 3k and then drops to 18psi when over 3k ?

Pop’s out of exhaust could be injector timing issue , ignition timing issue, (cam sensor/ign module/or ??) valve spring issue/, or etc also.

Saw the same issue last year. Fuel filter was clogged. Hope yours as simple. Isn't there a hidden filter on the 500EFI's?

Probably has a bad mechanical pump.

I swapped the fuel filters from my other motor, they spin on above the lift/mechanical pump

I made sure fuel filter was completely full and turned key to run the elec pump and still no change in psi.

maybe my gauge is reading wrong, I can try and change the gauge or use a mechanical gauge on the engine? Test the fuel pressure with mechanical gauge at the fuel dampener or somewhere else?

appreciate all the advice guys

#4 is the schrader valve on your fuel rail for using a fuel psi checker. You can rent for free auto part stores like Autozone.


https://cimg4.ibsrv.net/gimg/www.off...6c9c6076ec.gif

I will check the pressure with a mechanical gauge to verify what it actually is. Thanks for the diagram

Was psi 18 at idle too ? Or just when motor exhibits the issues over 3k ? I later added this to my post, you prob missed it.

Dont you have another electric fuel pump before the water/fuel separator? I do, and needed to change it 2 weeks ago for same problem

Yes, it stays around 18 no matter what RPM

There is a mechanical lift pump attached to the water pump that supplies fuel from the tank to the fuel filter and electric pump. Does not have 2 electric pumps

Have you checked the oil level in the fuel pump?

I have not, if fuel was leaking into fuel pump, would that affect fuel psi at the rail? it would only be able to leak so much until that reservoir would be full of fuel correct?

15 is also a fuel filter, they need changed as well.

I was told 15 is only a fuel "dampener" to give more of a consistent fuel flow. I can replace that next or would it be possible to somehow bypass to test if its faulty/plugged? I guess I could test it with the one off my other engine to test too.

A fuel dampener is a regulator that’s not being used to adjust fuel psi.

#15 in below microfiche page is a fuel filter.
see:
https://www.mercruiserparts.com/bam/subassembly/31341/7595/110

#20 is a fuel dampener. It’s outlet is blocked off.


https://cimg0.ibsrv.net/gimg/www.off...dbd8439040.gif

The actual regulator (one that set’s the psi) is #15 in this microfiche pic:
Also see:
https://www.mercruiserparts.com/bam/...31341/7595/120


https://cimg5.ibsrv.net/gimg/www.off...ce88b5f96e.gif

right, I replaced that regulator as well as the elec fuel pump in the cool fuel system. How could the metal filter that as the back of fuel rail get plugged or fail?

How does a filter back there get plugged ? Debris after the fuel water seperator filter. From degrading fuel / fuel line / fuel pump/ fuel pump modules : etc.

You should see all the crap i find in filters after the sepetator filter. These pics from various fuel systems (4 different boats) just this year ;


https://cimg7.ibsrv.net/gimg/www.off...878d7fbc8.jpeg
https://cimg8.ibsrv.net/gimg/www.off...0ab1e5db6.jpeg
https://cimg9.ibsrv.net/gimg/www.off...013198433.jpeg
https://cimg2.ibsrv.net/gimg/www.off...bf68bb148.jpeg
https://cimg5.ibsrv.net/gimg/www.off...e4ecdbe39.jpeg
https://cimg6.ibsrv.net/gimg/www.off...711d6e777.jpeg
https://cimg7.ibsrv.net/gimg/www.off...d85af45a9.jpeg
https://cimg8.ibsrv.net/gimg/www.off...604212790.jpeg
https://cimg9.ibsrv.net/gimg/www.off...d1a5d8851.jpeg
https://cimg0.ibsrv.net/gimg/www.off...dc38d4a46.jpeg
https://cimg1.ibsrv.net/gimg/www.off...c3ebff15c.jpeg
https://cimg5.ibsrv.net/gimg/www.off...a21ede1f6.jpeg

Well I swapped the rear metal filters and no change either. I will get a mechanical fuel psi tester this afternoon to verify my psi. When running on the hose at idle now I’m only seeing about 12-15 lbs on my gauge, doesn’t not increase with rpm. If my mechanical lift pump is bad, could that cause this issue or would I net see fuel at all to the electric pump if the lift one is bad?

again, appreciate all the help guys

Ok, so I just cracked the fill plug for water/fuel pump and it is over full of fuel/oil mix. Definitely a lot of gas in there. Lift pump must be leaking and not putting enough pressure to elec pump?

That is fairly common issue with those. Time to replace, I do not think they are rebuild-able.

I have early HP 500EFI's, they do not have the mechanical pump just the electric. They can sometimes get vapor lock and loose prime. I need to add the electric low pressure pumps to mine.