Engine backfiring

[miller]

I've inspected the hoses from the tank to the fuel rail and they all seem to be in good condition without anything obvious causing an issue. I pulled the pickup out of the tank but it does not come all the way out. Do I need to unscrew the bolt at the tank (where i added the arrow)? I thought i'd ask before i create another issue. I'm planning to take the boat on the lake tomorrow with the volt meter on the fuel pump.
Thanks,
Ryan

gas_tank.jpg

[miller]

It looks like the external nut will come off (at the end of the arrow), but this does help me out since the hole will be the same size which is not large enough to get the filter out on the end of the pickup. Any thoughts? It seems like there has to be a way to get to this filter.

[miller]

I pulled the tube out intake hose out and it is not blocked. I also replaced the high pressure fuel pump and tested it today and I am still having the same issues. Whats next?

[boatwakes]

Replace the anti siphon valve at the tank fitting for the engine pick up with a regular npt to barb fitting. After watching the video I believe that's part of your problem.

[miller]

Thanks boatwakes, I replaced the anti siphon fitting with this one (http://www.westmarine.com/buy/west-m...es--P013854898) thinking it might be an issue about a month ago, but i had the same issues. My thumb is on the new one in the picture above, fyi. So, I should replace the fitting with something like this (http://www.amazon.com/Derale-98101-M...oductDetails)? Other than the hoses, the only part that I haven't replaced is the low pressure pump. Could that be causing my problem? This has been a frustrating issue!

[miller]

I was doing some more "research" today and came across this article http://www.bakesonline.com/images/Me...mpMaintain.pdf on how to maintain my low pressure fuel pump. Is it possible that the screen/impeller is blocked which is causing my fuel delivery issue? i guess there is only one way to find out, but thought I'd see if anyone has seen this issue. Still searching for a solution and my time is running out. I have about a week left until I need to get my boat winterized for the winter.
Ryan

[miller]

New season, same issue! I had my dealer replace the low pressure pump and they test drove it and it worked great last Monday. I took it on the lake on Wednesday and the same issues surfaced. I met the mechanic on the lake on Thursday and the boat ran perfect for over an hour. I went out Friday night and the same symptoms surfaced immediately. I took the boat out yesterday and same issues. Yesterday, I put a volt meter on the high pressure fuel pump and the voltage remained the same while the fuel pressure dropped. Any new ideas? I'm thoroughly frustrated at this point...

[chpthril]

Ignition

[miller]

Thanks chpthril. I just pulled a plug and it is an AC Delco 41-979 plug. My MarinePower manual says my plugs should be the AC 41-932. It looks like AC 41-932 plug was replaced by the AC 41-933. Could this be causing my problem? The plugs were replaced as a part of the work performed by the dealer when this issue started. It seems odd that is would run good some times but not others.

[boardman74]

Another Idea I would strongly suggest is trying another dealer. If you want details why I suggest that shoot me a PM.

[boatwakes]

Miller, if you have access to a skiff fuel tank (approx 6 gallons) connect it to the engine and see if the problem follows. If so, we're on an engine related issue still and nothing to do with the tank, anti siphon or anything before the low pressure fuel pump. Connect the tank directly to the hose barb that the boats fuel tank connects to at the filter. It's acting like there is an intermittent blockage in the fuel line. If it runs fine on the separate tank, keep filling it up to see if you can replicate. If not, the problem lies in the boat's fuel tank or fuel connection line.

[Wakeman22]

Ok.

While searching for my issues I came across this thread. My boat is acting the exact same way.

Miller, Have you figured out your boat? This problem has been an off and on problem to me for the past 2 years. I thought bad gas however good fresh gas only works for a short period of time if at all.

[miller]

A quick update: I water tested it on a portable tank last week and I still had the same issue. I had another mechanic take a look at it and he found the connection for the newly replaced low pressure fuel pump was bad and the low pressure fuel pump was not running. I took it out this morning for the first time and it ran perfect. So, i'm cautiously optimistic that this was my issue. I have a hard time understanding why it would work great one day and then not the next, but as of now it works. I'll need to take it out a few more times to confirm that it is indeed fixed.

[miller]

Wakeman22, i started out thinking it was the bad gas but it wasn't until i saw the drop in fuel pressure at the engine rail that I ruled out an issue with the gas. I purchased this fuel pressure gage (http://www.amazon.com/Actron-CP7818-.../dp/B0006V2BI2) and it was super easy to confirm that it was a fuel pressure issue and not a gas issue. The gage connects to the engine rail using a Schrader valve like what you have on a bike tire. You just have to be careful to release the fuel pressure in the gage before you disconnect it.