6V92 stalled - need advice asap

[bobk]

Hey guys, I need some fast advice.

I'm cruising north and lost one of the 6V92's in the Alligator-Pungo canal (NC). It sounded like lack of fuel when it went down. It restarted once and ran a few minutes and stalled again. I tried priming with the electric pump and no luck. We limped back to Dowry Creek marina in the middle of nowhere only to find the only mechanic within 100+ miles is away until Sunday. I'll R&R the fuel filters in a few minutes, but am not hopeful They only have a few hours since the last change and both fuel deliveries were from sources that are known to be fresh.

Any ideas on where to look? All ideas appreciated.

Bob
Chateau de Mer
1981 48 MY

 

[Avenger]

How long did it sit before you tried the re-start that was succesful? If it sits for a while, let's say 15 minutes, and seems okay for a bit then stalls again I would suspect fuel restriction. If you have a hand primer you can usually feel pressure when on a pumping stroke, and/or vacuum on the suction stroke. If you feel heavy vacuum it's a restriction. If you can never get pressure it may be an air problem. Do you have any clear tubing aboard?

Other than that go with the basics. Is it definitely drawing from a full tank? Are the shutoffs in the proper run position, no issues with solenoids? Does it stall in gear, but run in neutral? If so, can you turn the propshaft by hand?

Just some ideas, not easy to do diagnosis from 1000 miles away.

Good luck and I hope this helps.

 

[captddis]

Make sure you change the secondaries too.

 

[Canuck Dennis]

Check for a faulty fuel pump also, not sure about the 6-92 series but on the 12v series you can put a small mirror under the pump and check if it is turning,
you can also remove the return line to see if fuel flowing there.
may also be a stuck injector although fairly rare happening.

 

[Genesis]

Probably a fuel restriction or air leak somewhere.

Open the Racor (if you have those) and see if there's fuel in it or air. If fuel, odds are its a restriction. Do you have vacuum gauges on the RACORs?

If the fuel pump itself is hosed (it CAN happen) the engine will not run at all; you HAVE TO have positive pressure in the rail or it won't start.

That it starts and runs for a while strongly implies either a suction-side restriction in the fuel line (a blob of crap that got sucked into the pickup, for example) or an air leak somewhere, and a fairly bad one too if it killed it entirely.

A stuck injector won't keep the engine from operating at all, although it will run like hell with one cylinder not firing - but it will run.

 

[Pascal]

i agree with the secondary, how old is it?

check the priming pump to make sure it's actually pumping, most electric pump have a screen on the inlet side that can get dirty. it's easy to pull the outlet side to make sure you have flow.

I believe that if the engine fuel pump was bad, the engine woudl run on the priming pump if you keep it on.

obvioulsy, try switching tanks on that engine...

 

[bobk]

It looks like there is a pluggage at the fuel supply selector valve before the priming pump. The pump will not run on either tank. If I break the supply line to the pump it sucks air good. The Racor was down about one inch when I opened it.

I'm now trying to pull the square pipe plug on top of the valve to see if I can clean out any crap in it. It's a bi@@h to open it! Any other ideas? The location makes it real hard to pull the fuel lines to and from the valve and it is lower than the top of the tank so fuel might siphon out. The fuel supply diagram doesn't show a valve on top of the tank at the dip tube.

Bob

 

[bobk]

I forgot to add that both primary and secondary fuel filters were changed in March.

Bob

 

[captddis]

Did you check the check ball in the racor?

 

[Genesis]

Bobk, find someone with a vacuum tank, connect to the OUTLET side of the RACOR and pull a full vacuum on the line. It will PROBABLY pull through. Get a REALLY GOOD vacuum pulled and hit it "all at once"; don't open that valve slowly, slam it.

You can blow it out with compressed air but that doesn't help as the glob will go back into the tank and plug it up again!

 

[bobk]

Good thought Karl. I just checked with several places and services in Bellhaven, NC and no one has anything, pressure or vacuum, so I'm going to try to disconnect the lines to the selector valve and run a small snake through them.

Bob

 

[34Hatt]

Do you have a dinghy pump or air pump for rafts. I use that in a pinch to get home. Turned out it was a bottle cap in the bottom of the tank
So vacuum doesn't always work.
It was in there a long time and then found the pickup tube

 

[mobilemn1]

Bob,

If you need any further assistance let me know, I can get air to you in about 45min. I am in Williamston and that is how long it would take me to get to you. I have a small air tank if that would help and probably any tools you may need.

Let me know.

 

[bobk]

Well, I'm now more confused.

I broke the line from the selector valve to the priming pump and fuel siphons easily from either tank so I now believe there is no blockage in the valve. When I run the priming step, the pump runs a few seconds and then slows to almost stalled. I guess it is possible I have a bad priming pump, but I don't like coincidences. I also broke the line to the Racor and ran the priming pump and no fuel flowed. I put a snake through the hose and it was clear to the first metal elbow.

What's left. Engine fuel pump? There is a sensor of some sort on the secondary filter. Could this be involved?

Does anyone know of a DD mechanic anywhere near Bellhaven? The marine engine guy that the marinas use is away for several days.

Again, many thanks for all the advice and offer to help.

Bob

 

[mobilemn1]

Bob, give me a call 2522176558, trying to find you some local help

 

[Timm]

I have 8v71's and had a similar problem. What I did to prove and or eliminate different components follows below. I think the sensor on the secondary filter housing you are referring to is the pressure switch that when fuel is flowing, closes and provides voltage to the engine hour meters.

The following process is to eliminate non-engine components. The concept is to bypass any exterior fuel components and to see if you can get the engine to start and continue to run from a portable fuel tank.

- remove the sensor/pressure switch on the side of the secondary filter housing.

- rig yourself up a 3/8" brass barbed connector and screw that into the filter housing where the pressure switch was. Don't worry about gooping up the threads since it's just a temporary connection.

- get a 36" piece of 3/8" clear hose and a couple of hose clamps

- attach the piece of hose to the barb with clamps

- get a 5 gallon tank of fresh fuel

At this point you need to try and force as much fuel into the secondary and the fuel rack. You'll feel some back pressure as it gets filled up. You might save some time and remove the secondary filter element and fill it up as much as you can before forcing the fuel into the engine.

Make sure the fuel hose is filled with fuel and then put the open end into the fuel tank keeping the other end attached to the secondary filter.

See if you can get the engine to start and keep running with this set up. Keep in mind that 5 gallons of fuel will go pretty quick. You should be able to see the fuel flowing through the clear hose.

A Detroit Diesel mechanic told me about this and said: if you can't get these engines to run out of a portable tank, there is something internally wrong. Fuel pump, plugged injectors, etc.

If it does start and remains running, you've eliminated fuel related componets physically on the engine.

 

[doc g]

The "sensor" on the secondary fuel filter canister is for the Hobbs meter ,hour meter. I would avoid breaking lines apart and get a vacuum on it as Karl said . If you blow it thru you'll end up with it clogging up at the worst possible time ,remember Mr Murphy?? Try a shop vac or one of those small DD primer pumps hooked to the line to provde suction . It also sounds like your prime puymp may be bad . The more lines you open the more possible air leaks ...............Pat

 

[bobk]

Tim, how do you pressure the fuel into the secondary?

Bob

 

[doc g]

Bob , I've used a el cheapo fuel pump from Trac Auto with fuel line on it . Tap into the system wherever there is a pipe plug (usually at the secondary fuel filter housing) and use a gas can of diesel , I plumbed the fuel pump with a fitting that fit right into the secondary filter housing ( the pressure side of the pump to the filter housing )and used alligator clips on the leads to a 12V source. You can prime the filter and the rack with that . I did it on my old boat every filter change . ........Pat

 

[Genesis]

The secondary filter is under PRESSURE - about 60psi - when the engine is turning! CAREFUL! Spraying fuel is at minimum a hell of a smelly mess.

You can stick a HAND PUMP suction side on the outlet of the RACOR (detach the fuel line going to the fuel pump from the RACOR) and pump. If fuel flows you've eliminated from the tank to the fuel pump on the engine.

If that test passes it is VERY LIKELY the problem is the engine fuel pump.

That pump is a little gear pump with an integral relief valve that controls pressure. It has VERY tight tolerances internally but is mechanically a very simple device. If the relief valve sticks open it will produce essentially zero pressure and the engine will run like crap, if at all. This is an unlikely but possible failure mode, but if you can draw fuel through the filter using a hand pump...... BTW beware rotational direction if the pump is bad when you go to replace it.

The more likely given the symptoms, as noted, is that there is a restriction in the suction side of the system. You have to either find it and mechanically remove it or suck it through. If you blow it back into the tank it WILL bite you again. If you need to go NOW and can take that risk detach the INLET side of the RACOR plumbing, attach compressed air, and blow backward towards the tank. The heavy copper used by Hatteras from the factory is rated for refrigeration-style pressures, so putting 50psi or so on it is no big deal. BUT - all that does is blow the crap back into the tank!

The ideal fix is a vacuum tank. Detach the OUTLET of the RACOR, attach the vacuum tank TO the RACOR, and slam open the vacuum valve. This SHOULD drag whatever is plugging the line into the RACOR where it will be trapped, and solve the problem. If it fails you're no worse off than you were before, as a full vacuum is only 15psi, so the option to blow it backward still exists.

Another option, assuming you do not think the problem is in or on the pickup tube, is to detach the fuel line from the tank, put a hose on it to direct it into a catch can, then apply air pressure BACKWARD from the RACOR toward the tank. This will expel ALL the fuel in the fuel line into the catch can - along with whatever is plugging it up. This will not work obviously if the obstruction is in or on the pickup tube.

Getting the pickup tube out of the tank is a real pain in the ass. It can be done, but its not easy.

BTW I am assuming you have checked the RACOR bowl and it is not full of water, right? RACORs have a floating ball in them that will shut off the fuel (intentionally) if the bowl fills with water.....