M-12 universal stalling at 2-5 knots......

[Jtcf78911]

Dear friends in sail.

The M-12 Universal diesel in my 1985 O'Day 28 has been acting up of late, namely stalling out whenever I try to push her beyond the lowest acceleration point. A little bit of a challenge when you are heading out the Merrimack (tough bit of river in Newburyport MA) and suddenly find you have no engine... At purchase of the boat the now previous owner specifically pointed out the exhaust discharge to me, noting that if I saw black water coming out that I was pushing the motor too hard and therefore kicking out unburnt fuel... Seemed logical, but now the engine is dying even at low acceleration, never mind my trying to push her up to 5 knots (which interestingly enough, I had done for nearly half a day on my sail down from Portland, ME to Massachusetts.) The engine will sit in neutral and idle without issue. I put a fresh tank of diesel in, as well as some additive-cleaner, but to no avail. Planning to change gas filters this Fall. Greatly appreciate any guidance on this front. I can't be worrying about engine support every time I go out for a sail...

Tom O'Day 28

 

[shemandr]

I'm probably least qualified to respond but I would check/change the fuel filter today.

 

[Stu Jackson]

Do you know when the last time the exhaust riser (pipe between the exhaust manifold and the muffler) was replaced?

 

[Benny17441]

Let's play the odds; 1) the fuel filters are dirty and the fuel flow is inadequate at higher RPM, 2) the fuel tank vent or pick-up tube are obstructed, 3) a fouled exhaust mixing elbow. Now if the engine had been running fine earlier in the day and you were out coastal cruising chances are that with boat motion sediments at the bottom of the tank were dislodged and contributed to clogging the fuel filter and water separator. Start at the simplest and least expensive causes, check the fuel tank vent, disconnect the fuel line at the water separator and check for adequate flow and if not blow air back into the tank to dislodge any blockage at the pick-up tube. Then replace the primary and secondary filters after draining the water separator. Lastly remove and clean or replace the mixing elbow. There are a few other causes for the symptoms but their occurrence is infrequent and require more technical diagnostics. Hopefully your problem lies within the above listed causes.

 

[kloudie1]

Only thing I'd add is that it could be a small air leak between the tank and the lift pump suction. Look for evidence of diesel weepage along the hoses and at connections. Some leaks in the suction side can leak air in without leaking diesel out.

 

[Capt jgw]

Of you find low fuel flow from the tank, there's probably a screen at the end of the pick up tube that's clogged. Common problem. Just pull the tube out and remove the screen. Don't put it back on, you don't need it. That's what the filters are for.

 

[Davidasailor26]

Our 28 didn't have a screen or place for sediment to block at the pickup tube, but it did have a screen on the electric fuel pump. That pump is before any other filters. If you turn the ignition key in, before starting the engine, you should hear the electric pump clicking about once per second. If it is slower than that, check the filter there.

 

[Stu Jackson]

That pump was always put in the wrong position by Catalina and many other builders.

Racor first, then pump, then to engine. It takes all of 30 minutes to replumb it correctly - buy a foot (depending on where your filter & pump are, they're usually pretty close) of hose and a barb fitting with some clamps.

You might be interested in these items, many of which apply to your engine as well:

Critical Upgrades http://c34.org/bbs/index.php/topic,5078.0.html

Our 28 didn't have a screen or place for sediment to block at the pickup tube, but it did have a screen on the electric fuel pump. That pump is before any other filters. If you turn the ignition key in, before starting the engine, you should hear the electric pump clicking about once per second. If it is slower than that, check the filter there.

 

[Bill Roosa]

Also check your air filter. not likly that is "just got plugged" but the problem has been getting worse over time. If the fuel system and air filter check out then it is time to pull the exhaust elbow and check for blockage.

 

[Jtcf78911]

Excellent advise across the board. I was going to start with the air filter as I had read (Casey) that black discharge likely means inadequate air flow. I did stick my finger into the air inlet and it came out quite black..so hoping if may be that simple. However, the fact that it's not a consistent issue makes me suspect of this solution. Is it possible to actually clean out all the fluid/matter that may be living in the fuel tank? Feel like I should start at the source of gas flow and work my way forward. Thank you gentlemen for all the great pointers.

 

[2taylorscotts]

First, I'm not a marine diesel mechanic. Lucky for me my son is! (A Chief Engineer no less!) I too have an M-12 which was giving me indigestion, so I asked him what I should look for if the problem was injectors. He replied that if they were sticking I'd hear it and if they were leaking I'd be blowing fuel out with my exhaust. That would be black smoke. I'd certainly try all the other preliminary checks that have been suggested. If nothing else they are appropriate preventive maintenance. If the problem persists and you have black smoke, particularly at high RPM's I'd check the injectors. Fortunately, my problem was valve adjustment because injectors for that little piggy are VERY expensive. IMHO The PO was also blowing smoke!

 

[Jtcf78911]

First, I'm not a marine diesel mechanic. Lucky for me my son is! (A Chief Engineer no less!) I too have an M-12 which was giving me indigestion, so I asked him what I should look for if the problem was injectors. He replied that if they were sticking I'd hear it and if they were leaking I'd be blowing fuel out with my exhaust. That would be black smoke. I'd certainly try all the other preliminary checks that have been suggested. If nothing else they are appropriate preventive maintenance. If the problem persists and you have black smoke, particularly at high RPM's I'd check the injectors. Fortunately, my problem was valve adjustment because injectors for that little piggy are VERY expensive. IMHO The PO was also blowing smoke!

Thanks. Lot's of good advice and things to check...your injector thought has me nervous...but we'll see how she plays out. I just can't have the thing dying on me in a tight mooring field or while on the damn Merrimack River (which will take a motor-less sailboat wherever it damn pleases). Best. Tom O'Day 28

 

[jibes138]

JTCF, if you have an electric fuel pump that is cylindrical in shape, they typically have a fuel screen on the bottom that needs to be cleaned/replaced just like a fuel filter. You can get these at a NAPA auto parts store. Since your fuel pump is first in line (mine was plumbed the same until I changed it) this screen will get all the gunk from the tank first. It is simple to remove and replace with a wrench and about a half turn. Restricted fuel supply will cause loss of power until your engine eventually won't run for lack of fuel.