Engine dying repededly

[handsumrob]

Good Afternoon all! My boat has been running fantastic all year until this weekend. I was out on Long island sound in some pretty good swells motoring at about 2500RPMs. about an 1.5Hr's in the motor started loosing RPMs and died. I went below and didnt see anythign evident so I opened the bleed on the secondary filter and started to prime the lift pump. It was taking a long time so I pulled the secondary filter bowl off which had very little fuel in it. I topped it off screwed it back on and went back to priming. Within a minute i Had bubles and then solid fuel. Closed that and primed the bleed right before the high pressure side. Once that was completed the engine fired right back up and off we went. It ran for about 5 minutes and dies again. This time i replaced the primary filter making sure all survaced were clean and no debris. I also did not see any indication of failure in the previous gasket. I also replaced the secondary filter and o rings. Primed the motor again it fired right up and off again. That lasted about 15 minutes and it died again. The day ended getting towed in.

Troubleshooting. I started today with troubleshooting. I check the fuel tank vent. CLEAR. I checked the Fuel pick up. Clear. I bypassed the secondary filter because all the bleeding i had done i overtightened the bleed screw and surely stripped it. I primed the engine with the secondary filter bypayssed and it will start and run for about a minute and then die again. I disconnected all the return lines and made sure the were clear as well as the return on the tank. The way the returns lines are run is a hose comes from the the most aft fuel injector down to a T fitting. from that T fitting 1 hose goes back directly to the tank and a second hose goes forward to what looks like the  begining of the high pressure system just forward of the seondary fuel filter. it is item 23 in the photo I attached. This is secured with a check valve bolt. The only odd this I noted is that this check valve seems not to beoperating. Although i'm not really sure what its correct operation would be.

I am not sure where to go from here or what else I can potentially bypass to isolate the problem. Any help would be appreciated.

[Charlie-Bravo]

Infuriating isn’t it? 

Not model specific thoughts below .. what model is it ?

In your early description you mention some pretty good swells, possibly a clue to fuel tank contamination, as the bouncy conditions stir up anything horrible in the fuel tank.

You then bleed the system and she fires up straight away, a good sign of a healthy set up ….. once it has fuel.

The secondary filter being near empty would indicate fuel starvation, and this is the biggest clue you give.

The return to tank line can cause complications, but generally they work well, but as you suspect, can be a cause of trouble, but they don’t generally empty the secondary filter of fuel, they just return all the fuel to the tank , stopping the engine in the process.

The clues given , led me to suspect the lift pump having a suspect diaphragm (if yours is of this type) a small split maybe , taking a while to bleed the system, allowing engine to start and run, but not able to keep up with demand once running was a first thought, however, it doesn’t really fully account for the air / lack of fuel in the secondary filter.
Air getting into the fuel line would account for the near empty secondary filter, and also , once bled, allowing the engine to run for a bit, until the fuel in the secondary filter is low, replaced by air, stopping the engine.

The fuel line to the primary filter, and up to the lift pump is under negative pressure on most systems, the fuel being sucked through it, once at the lift pump it gains a small positive pressure through the secondary filter before getting to the seriousness of pressure at the injection pump, so once under a positive pressure is more prone to leakage than air ingress. It is possible for air to enter the negative pressure line without leaking fuel, making it harder to detect the failure , and this would account for your description of the troubles to my mind, and could be as simple as a slightly loose pipe connection or failed olive in a compression joint, also a suspect is the filter connection of ‘spin on’ style filters , or the top of a cartridge type, or the filter housing bleed screw.

Does your primary filter have a clear bowl so you can see if any air is lurking in there? if not perhaps think of an upgrade to this type. 

Do post further clues should they come to mind, and interested to hear the result of your further investigations.

Hope the above at least gives some food for thought, if not the complete answer.

CB

[Camira]

Sounds like diesel bug to me and the small filter on the end of the pick up hose in the tank needs taking out and cleaning and the diesel in the tank needs treating or if very bad polishing. A bit of a pain I know, I got away with shock treating mine and now make sure that every time I fill up I add the treatment.

[handsumrob]

Jul 30, 2023 8:17:18 GMT Camira said:

Sounds like diesel bug to me and the small filter on the end of the pick up hose in the tank needs taking out and cleaning and the diesel in the tank needs treating or if very bad polishing. A bit of a pain I know, I got away with shock treating mine and now make sure that every time I fill up I add the treatment.

Thanks you. I found no evidence of diesel but when I removed the pick up and nothing on the filters. I shock the system each year as well as add treatment every time I add fuel.

[SaltyDog]

Had exactly the same on the genset: engine dying out repeatedly/starts up a bit and dies fast. It turned to be the small valves in the fuel feed pump were stuck. I just unmounted the thing, opened it up and cleaned the tiny valves (tell tale sign: if you operate the manual lever on the feed pump, while the air bleed screw/nut (#13?) is open, diesel should squirt out. If it doesn't the fuel filter is clogged or your valves are stuck).

Mine started fabulously after the operation, I hope yours does too!

Note: it is the fuel feed pump you are after, do NOT touch the high pressure pump!!! If you can't tell the difference, stay away and ask a mechanic to check things out!  In your drawing the feed pump is to the right of #4..

[Valor323]

 The diagram you supplied is that of a 3gm30 variant, so I will assume that is what you have.

On a previous vessel which had a 3gm30f, whenever I had a weird, intermittent diesel issue, filters are an automatic change out, followed by bleeding the fuel system. 

If that doesn't do it, I will always try to start/run the motor from a known clean fuel source, like a 5-gallon jerry jug.  If it runs after that, the problem is located before the disconnected line and your jerry can and you can focus your efforts there. If it doesn't start after that, something is clogged, or a part has failed after the jerry jug.

If you add a low (5) psi inline fuel pump immediately after the jerry can and the motor works, then you have a delivery issue and you should maybe check the lift pump or look for a clog/air. This is assuming the engine has been bled and the filters are clean. This is just the way I do it. It's kind of vague but it rules out areas to ignore so I don't waste a lot of time. It has served me well over the years. I leave the hose with the attached fuel pump in a locker and ready to go, if I should run into a problem along the way. 

Additionally, the lift pump on a 3gm30 is a diaphragm pump. If the diaphragm fails, it will dump fuel into the crankcase. Pull your dipstick and check for elevated levels and the smell of fuel. That happened on mine.

Personally, it sounds like after you are manually repriming the fuel system and the engine is running, you are running out of fuel 10 minutes later. Buy a BS 5psi inline fuel pump from amazon, feed it from a 5-gal fuel jug with new fuel and connect it directly to the mechanical lift pump. If the engine remains running, it's your lift pump. I had the same issue and that is how I diagnosed it.

Good Luck!

[rxc]

I had similar conditions twice. The first time was when I bought the boat, and it turned out to be plastic shavings in the fuel tank, clogging the metal pickup tube where it makes a right angle turn out of the tank. The dealer who sold me the boat installed a replacement Racor filter and I had to clean out the filler tube twice after that.

The next time it happened was about a year after I dropped the tiny plastic seal on a bottle of diesel treatment into the filler hose. The seal was eventually caught on the end of the pickup tube. When the engine stopped, the seal dropped off and the engine ran fine. I eventually removed the seal when I had to open up the fuel tank to replace the filler hose fitting gasket, which had swollen and leaked. The seal was right there, floating on top of the diesel fuel.

I suspect that you have debris in the tank, which is accumulating and blocking the fuel flow. It may require you to open up the tank and clean it. Not a pleasant job.

[lateron]

Hi
Just to add to all the advice given.
I had an intermittent fault on my Yanmar 2gm 20 and tried new lines filters etc before I got the lift pump checked and that's what it was, an intermittent fault on my lift pump in my case. But replaced the pump 2 years ago and all good, touch wood, since then.
Cheers
Ron