Fueling issues!?! Help!
 

I have a 2000 Imp Viper with twin L29 454's. I recently purchased the boat and took it out several times before I ran into any issues. My fuel gauge is apparently about a 1/4 off and I found this out the hard way. Got it towed to a gas dock and refueled and either motor would not start. I attempted to prime the motors with the key several times and could not get it re-started. I let the boat set while I ran home to grab my fuel pressure gauge. Hooked the gauge up and was only getting about 10 psi, eventually I was able to prime the system on both motors and get about 40-43psi to the test port on the fuel rail. Both motors started right up and would hold 35-38 psi. PHEW. All ok. Lesson learned...

This weekend I went out Friday and the boat ran great. I took the boat out Saturday and got to a buddy's dock, hung-out for 3 hours and the boat would not start. Eventually I got my port motor to re-fire by working the throttle up down and priming the engine. After several attempts I got the starboard side to run. Once they quit stumbling the boat ran great at 55-60 all the way home without any issues. I figured maybe I had picked debris up from running the tank low and the fuel filters were my issue. I replaced the fuel/water filters before hitting the water on Sunday. Primed the motors and they started up and seemed to run good. Took the boat up about 10 miles, had lunch, went back to the boat and only the starboard motor would run. It did stumble at first but cleaned out. The port motor would start and stumble but not stay running...

This time I brought my fuel pressure gauge along and the port motor was only at 10-15psi while priming it. Eventually I got rail pressure to 40-43 by priming with the key and working the throttles while trying to start. It finally started and ran for about 20 secs at 35psi. It started to stumble and the fuel pressure dropped from 35 all the way to 14 psi and it died. Limped it home on the starboard motor as it would not re-start. I would say I have bad fuel pumps but its hard to believe that both failed at the same time. Any advice would be appreciated. I have never replaced pumps on the L29 efi engines and I am guessing the bank 1 manifold has to be removed to do so? HELP!

Sounds like vapor lock or bad anti siphon valves to me but I'll let others chime in....you may have also sucked a bunch of crap off the bottom of the tanks when you ran it out of gas as well...I'd start by checking the anti siphons at the tank, changing fuel filters, and see what you have from there

1) Remember that your tank(s) are "V" shaped at the bottom, and your gauge only reads linearly. The second "half" of the tank goes quickly. At 1/2 tank, you know you need to get gas. At 1/4 tank, you better be on your way to get gas. Less than 1/4 tank, and you better have the gas dock in plain sight. Old USCG rule: 1/3 to get there, 1/3 to get home, and 1/3 in reserve. The only time you have too much gas in when you are on fire. And last, remember that rough water will drink twice the amount of fuel as a normal cruise.

2) You ran it so low, that you probably sucked in all the random garbage from the bottom of the tank into the fuel pumps. Best to replace both of them for good measure. Be sure to replace your fuel filters/water separators too.

Can anyone drop some knowledge on the fuel pump replacement procedure for the L29 motors? I have already replaced the fuel/water separators and plan on replacing the anti-siphon check valves. I have the pumps on order in case this doesn't fix it but would like an idea of what I may be getting into!

Access will be your biggest hurdle as the pumps are buried down low in the cool fuel module.

Wasn't sure if a manifold typically had to come off? I'm assuming under the LH (bank 1) manifold is where the module is located?

Im not sure about the motor you have, but my 500EFI had to have 'booster pumps' installed to make the vapor lock go away. just replacing the original pumps did nothing. Problem so widespread that Merc actually created a 'kit' complete with mounting and hoses that can be installed.

After i installed, never had the problems you describe again.

Facing the engine they are down low on right hand side (odd bank, boat's Port side).

https://www.mercruiserparts.com/bam/...31918/2705/110