Hey all,

I'm going to redo this since the last thread was pretty lengthy and I've since narrowed things down quite a bit.

Setup:
2004 Ebbtide 23' with 6.2 / B3 (Booster fuel pump + Cool Fuel setup)


Symptom:
- Boat will run fine under 3200rpm's all day. Once you get over 4000rpm's boat may run fine for 10 minutes or 1 minute. Then fuel pressure will drop from 38psi to erratically dropping from 8psi to 0psi. The high pressure pump starts making a sporadic whirring noise like its sucking up air.

- This issue seems to be temperature dependent. If blower is off and engine box is closed on a 90 degree day it acts up really bad. In the evening with the box cracked and blower on it might not show up at all. (Had a 3minute WOT run on Saturday evening without issues after having major flare ups all afternoon after 30 seconds WOT.) Throttling back will clear it up usually, but it seems like the hotter it gets the worse it gets and I might have to float for a few minutes before the pump sounds right. Engine temp always stays 158-166. I've only had a restarting issue twice and that was cured with just a couple minutes of cool down.


What I've done:
Between me and $500 to my local Merc mechanic I've done the following. (The Merc mechanic had the boat hooked up to a dyno for over a half an hour and couldn't get the issue to act up. Pressure on both pumps were within spec during the entire test.)
- New cap, rotor, plugs. (Just for good measure.)
- New fuel separator and new inline prefilter before boost pump.
- Verified no codes withing last 40 hours, and hasn't hit 'protect mode' ever.
- Check pickup screen / seal.
- Verified the check valve from tank was clean and set for correct pressure.
- Both fuel pumps operating in spec.
- Gone through 4 tanks of gas with various octanes, from different pumps, with different additives. (Stabil ethanol treatment, Red HEET, octane booster, etc...). Issue seems pretty consistent. Hard to keep the outside temps the same between tests for true consistency though...
- Never saw water in separator after changing multiple times.
- Cool fuel coil is always cool to the touch.
- Boost pump always feels relatively cool to the touch when the issue act up.

Any thoughts? I picked up a high pressure pump for a spare but am going to return it if that doesn't sound like the issue. Can a pump test in spec but then act up when hot? I just can't tell if the vapor lock is occurring before or after the high pressure pump. Basically is the fuel vaporizing in the rail, is the boost pump not providing enough fuel, or is it vaporizing between the boost and high pressure pump.

Grrrrrr... getting really frustrated here. This issue has pretty much ruined every boating trip this year since I'm freaked out its going to break any second. But after 40 hours on the clock this season it still behaves the same.

My guess would be a cracked pick up tube in the fuel tank.
With the boat in the water, the fuel will move around and allow air into the crack. On a prop dyno, the fuel stays at a steady level.

Good info.

I ended up replacing both the high pressure and low pressure pumps without luck . Then I bought a 6gal portable tank and ran directly off of it. The problem went away.... So it is looking like air incursion, anti siphon valve, or a pickup issue. I tested the all but the last 8" or hoses for air incursion (using a clear filter) but didn't see anything obvious.

I'm going to remove the anti siphon check ball and remove the screen off the pickup then install the clear filter to see if I can get any crap out of the tank, or see if the issue disappears. (I couldn't see any visible cracks in teh tube, but its just pressed on at the top so I could see air maybe getting it.)

Thanks for the help. Almost $1,300 later, 3 ruined vacations, over 30 hours or researching and messing with it, and it might a periodically clogging pickup or bad anti siphon valve, which were the two first things I looked at but tested out fine originally....

I'll update when I get it figured out.