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Old 08-03-2022, 03:32 PM   #1
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Fuel Delivery Problems?

in 22 years of boating and boat maintenance, I finally have a stumper, so going to throw it out to you all!
On our shake down cruise a month ago, we anchored after 3 uneventful hours of cruising @1250 rpms on our OA 43 w/ twin DD 453s. That evening our Northern Lites 5KW genset wouldn't start. Just cranking and cranking. OK no problem, I'll have a look at it when we get back. The next morning we take off for home and after about 20 mins. of 900 rpm courtesy cruising, the starboard engine starts bogging so I shut her down, and then the port followed up doing the same. (On a side note, my fuel flow meter has been showing erratic readings on the port side, like 54 GPH).
Back at our home port after a long tow, I started going through the fuel system. I changed both the Racors and secondaries, again, after the spring maintenance. Removed the port tank inlet line on the supply manifold (pictured) and ran fuel through it from the starboard tank using a small auto store fuel pump into a glass bottle to see if there was any blocking type material from the tanks. Nada. Primed the system then they both started right up. I haven't taken her out for a sea trial, since i haven't found the smoking gun yet and am a bit hesitant to be under tow again. So my working theory is this:

With both tanks at 1/4 full ( dipstick confirmed) the engine supply impeller pumps are not strong enough to pull the fuel out of the top mounted siphon tubes and I need to change them both (seems odd that both stopped working effectively at once), but that still doesn't account for the Genset not starting, which I haven't gotten to yet and may be just coincidence (I cracked a rib on vacation and am reduced to keyboard troubleshooting, hence the lengthy post) Another theory is that the return manifold (pictured) is clogged and not allowing fuel to circulate properly, causing them to bog down.
I am also getting ready to install an electric lift pump on each side to delivery 2-3 lbs of fuel pressure from the tanks (which I can also use for tank transfers). Good idea?
Any and all ideas/ suggestions are much appreciated!

Thanks and happy sailing!
Marc
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Old 08-03-2022, 04:31 PM   #2
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Old 08-03-2022, 06:27 PM   #3
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Are your fuel pumps the stock gear pump? Driven by the governor weight shaft? It's a positive displacement gear pump that rarely fails, and then only for a seal failure. The pressure relief valve lifts at 65 psi. Some filter housings have an extra port where a fuel gauge can be mounted.

From an old guy that's been around Detroits for a long time, I've never had a fuel pump failure. My guess at this point is you're sucking air at some point common to both engines. like the manifold.

You can install an inline electric pump, but it need to have the same flow rate as the stock pump. I have them on my engines for filling the fuel filters and as an emergency pump. I don't normally run them when the engine is running. I got mine on ebay and fit a 3/8" hose. Smaller size doesn't allow the stock fuel pump to have enough flow. You need above 25 gph to cool the injector tips properly.
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Old 08-03-2022, 07:01 PM   #4
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Hi Lepke,
Thank you for responding.
Yes, the stock engine mounted pumps are the only ones currently on there. I am installing two 12v 38gph inline pumps at each tank for servicing and tank transfers and was thinking they would "help" the possibly weak engine driven pumps. I do have gages on my Racors to show the differential pressure for clogged filters. Is that what you are referencing? They are showing normal. I will look into possible air being sucked in somewhere.
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Old 08-03-2022, 07:55 PM   #5
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Lepke is right. From the description of the engine stoppages, you are undoubtedly sucking air, and it only gets worse as the fuel level in the tanks decreases. I have had some experience on boats with standpipe fuel draws as your tanks are arranged, and I HATE them. Luckily, I have never owned such a system. Any fitting in the system which works loose or any pinhole in a standpipe will stop you, especially with the ill-planned manifold which effectively joins your two engines to a common failure point for fuel delivery. Whoever planned that failure point never had two engines fail as you just did. If that were my boat, I would remove all the fuel lines and that dumb manifold before I ever got underway again and replace the top-draw system with a bottom draw supply. If there are drain plugs in your tanks, you can connect bottom draw hoses there and lead then separately to your two main engines with a normally closed valved crossover line. between them. If not, it is not a big deal for somebody who has done it to safely install bottom draw ports. Generators fuel supplies are sometimes placed some distance above the main engine draws and/or have shorter standpipes than the main engines to avoid inadvertently drawing fuel below the main engine supplies again, sound like just what happened to your genny followed by the mains. Do yourself and your piece of mind a favor and rid yourself of this nuisance system. Rant over.

Oh, and welcome the heck aboard!
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Old 08-04-2022, 02:49 AM   #6
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Thank you rgano! That seems like good advice. I dont like the concept of breaking down so I will be going through each and every line and fitting. I do have an aux drain plug on each tank that could do for supply but I worry it will allow in too much bottom junk and water. Right now the standpipes are 2-1/2 inches above the bottom and I use the bottom ball valve drain to get debris and water out periodically. What do you recommend installing to prevent this from happening if I get rid of the standpipes?
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Old 08-04-2022, 05:13 AM   #7
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If you have top mounted fuel takeoffs on your tanks.... they could have anti-siphon valves up there. I believe the ABYC requirements are for anti-siphon valves or manually activated valves within a certain distance.

When I installed new fuel tanks, they came with top mounted anti-siphon valves. After a year or two...I had a trip from hell where the engine randomly shut down from fuel starvation like 13 times on the ICW between Ft Pierce Florida and Ft Lauderdale. Scary to say with some of those boat drivers.

Investigated and found the anti-siphon valves were sticky from diesel. They are really for gasoline...those rattle ball siphons for transferring fuel are the same...diesel makes them stick closed.

Check your setup, it's a long shot but when in doubt.
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Old 08-04-2022, 09:48 AM   #8
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Originally Posted by Msamsen View Post
Thank you rgano! That seems like good advice. I dont like the concept of breaking down so I will be going through each and every line and fitting. I do have an aux drain plug on each tank that could do for supply but I worry it will allow in too much bottom junk and water. Right now the standpipes are 2-1/2 inches above the bottom and I use the bottom ball valve drain to get debris and water out periodically. What do you recommend installing to prevent this from happening if I get rid of the standpipes?
I always wanted my fuel to be drawn from the very bottom in order to suck any debris or water out of the tank. That is what the fuel filters are for, to catch it. I want the tanks as clean as possible. Otherwise when you get out in bad weather the crap can get stirred up, sucked up all at once and clog the filters and shut you down. I would rather get small amounts out as it gets into the tank.
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Old 08-04-2022, 09:57 AM   #9
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Originally Posted by Msamsen View Post
Thank you rgano! That seems like good advice. I dont like the concept of breaking down so I will be going through each and every line and fitting. I do have an aux drain plug on each tank that could do for supply but I worry it will allow in too much bottom junk and water. Right now the standpipes are 2-1/2 inches above the bottom and I use the bottom ball valve drain to get debris and water out periodically. What do you recommend installing to prevent this from happening if I get rid of the standpipes?
Here's my thoughts on your fears of junk getting into the fuel lines from bottom fed fuel - so what. That's what filters are for. I run 2-micron Racor filter elements with a dash-mounted vacuum gauge giving me timely information about what's going on there, and I change the filter when the needle reaches 5 inches of mercury. When I initiated this idea on my Grand Banks, I was changing Racor 2-micron elements fairly frequently for a while. By the time I sold the boat a couple of decades later, my Racor primary 2-micron filters required changing every five YEARS. While installing a bottom fed system, you will be clearing out the current junk in the tank bottom, and will regularly suck anything new out and into the filters. It takes a long time for those asphaltines to precipitate out of diesel and gunk things up. With a bottom fed system, you are constantly clearing them out and keeping corrosive water from collecting where it can rust out your tank bottom - win, win.
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Old 08-04-2022, 09:58 AM   #10
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Originally Posted by Comodave View Post
I always wanted my fuel to be drawn from the very bottom in order to suck any debris or water out of the tank. That is what the fuel filters are for, to catch it. I want the tanks as clean as possible. Otherwise when you get out in bad weather the crap can get stirred up, sucked up all at once and clog the filters and shut you down. I would rather get small amounts out as it gets into the tank.
Aren't bottom tank draws an issue for USCG and ABYC? My 4 tanks are all top draws and work fine, not saying though that some vessels have piping setups that can indeed be problematic. Especially when the bottom of the dip tube becomes compromised.
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Old 08-04-2022, 10:15 AM   #11
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Aren't bottom tank draws an issue for USCG and ABYC? My 4 tanks are all top draws and work fine, not saying though that some vessels have piping setups that can indeed be problematic. Especially when the bottom of the dip tube becomes compromised.
Any USCG rules for fuel system draw being top or bottom draw is not going to apply to a pleasure vessel. Many USCG rules for "inspected vessels," like 40-inch tall rails, would be pretty much a nuisance on our recreational vessels.
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Old 08-04-2022, 10:35 AM   #12
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Aren't bottom tank draws an issue for USCG and ABYC? My 4 tanks are all top draws and work fine, not saying though that some vessels have piping setups that can indeed be problematic. Especially when the bottom of the dip tube becomes compromised.
For gas tanks, yes.
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Old 08-04-2022, 11:20 AM   #13
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The vessel originally had bottom draw fuel supply lines but they were converted way before me. I like the idea though since the racor filters are easy to change and the tanks would be kept very clean. This system has no anti siphon valves.
Thanks for all the advise!
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Old 08-08-2022, 01:43 PM   #14
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A thought on the generator not starting... with my Mainship once the fuel level drops to 1/4 full the generator shuts down or will not start. Manual says itís to prevent you from running the tank dry when on the hook.
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Old 08-08-2022, 02:07 PM   #15
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A thought on the generator not starting... with my Mainship once the fuel level drops to 1/4 full the generator shuts down or will not start. Manual says it’s to prevent you from running the tank dry when on the hook.
My genset draws from the main manifold, shared with the two power plants. Another reason Id like to ditch the manifold. When air gets in anywhere, the whole system is caput!
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Old 08-08-2022, 11:31 PM   #16
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If you want to check fuel pressure after the stock fuel pump, there should be a blocked off port on the secondary fuel filter housing, usually mounted on the engine. If you're going to mount a permanent gauge, use an oil filled gauge because of the vibration. The port is usually 1/4 but could be 3/8. Gauge is about $15 on ebay.
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Old 08-08-2022, 11:46 PM   #17
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Thatís a great idea! There is a 1/4Ē port at the secondary.
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Old 08-09-2022, 05:24 AM   #18
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If the fuel is unfiltered from the tank to the manifold and the tanks and engines share a common intake manifold, you may want to look for crud in the manifold. Had that happen to a friend of mine. If you have 2 tanks connected to the same manifold it may be worth switching to the alternate tank to check for reduced vacuum on one tank feed line versus the the other.

If I were going to use a manifold to feed the engines, the Racors would be between the tanks and the manifold.

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Old 08-09-2022, 06:55 AM   #19
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A thought on the generator not starting... with my Mainship once the fuel level drops to 1/4 full the generator shuts down or will not start. Manual says itís to prevent you from running the tank dry when on the hook.
We had the same set up on the green boat.

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Old 08-09-2022, 01:23 PM   #20
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I have a 1982 OA 43 with twin Lehman engines that I bought in 2000. Your fuel manifold looks familiar. I had many fuel problems over the years:
Clogged Racors, water in fuel. Clogged fuel line at an elbow. Three years ago I had the tanks cleaned, lines flushed and fuel polished. They literally cut an access panel in the top of the tanks and sent a man inside to clean them. He removed 5 gallons of reddish biomass goo from each tank. Things have been good since then. The boat is on the hard in Mexico for 5 months each summer. I always store it with full tanks to reduce condensation.
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