Diesel fuel starvation - troubleshooting steps?

[BrianSmith]

My reliable-as-can-be-for-three-years Isuzu diesel is dead in the water. After being away from the boat for a month, we returned a few days ago, and as part of our return-to-the-boat checklist, we started the engine and let it run for a few minutes, then shut it down. As always it started in less than 1 second, and ran smooth.

Today, we were going to leave the marina. Normal pre-departure checklist, instant start-up, smooth running, for about 4-5 minutes (just long enough to get a few hundred yards away from the dock, of course). Then it stumbled for several seconds and died. We were still in the harbour, so were still running pretty slowly - 800 - 900 rpm (vs. normal crusing of 1300). Made one attempt at a restart, which didn't work, so fired up the genset and engaged the get-home prop to get back to the dock. Let everything cool down for an hour or so, then started it - it started, but really rough, and didn't respond to advancing the throttle (still really rough), then it died. I tried one more time, and this time, after about 5 seconds of cranking, it didn't start, so I quit. (I have a water lift muffler, so I need to disengage the belt on the raw water pump before continuing to attempt to start it.)

I know it's not a clogged air filter, as I completely removed the filter prior to the first attempt at a restart.

I know it's not a dirty primary fuel filter (Racor 1000, 10 microns), nor a clogged fuel line to that filter, as the vacuum gauge on that filter didn't move a bit.

I'm almost sure it's not a dirty on-engine fuel filter, as I replaced that only about 3 operating hours ago, in October, just before we left for a month.

How should I proceed with troubleshoot? I'm thinking:

Step 1: replace the brand new on-engine fuel filter with another new one, on the off chance that the one I just put on is bad. If that doesn't end up being the case, then I'll keep it to be used the next time I replace this filter.

Step 2: disconnect the line from the lift pump to the injector pump and crank the engine, and see if I have good fuel flow coming from the lift pump. (How will I know if I have "good fuel flow"?)

Step 3. reconnect that fuel line, then disconnect one of the lines going to a cylinder, and crank the engine, to see if I have a good squirt of fuel every other rotation. (How much is enough?)

Does this make sense? Is there something else I should try, or should I do things in a different order?

Thanks for any input!

 

[Russell Clifton]

You didn't mention it but are you sure that all fuel valves and return valves are open? I have bumped mine closed while working around the engines and not realized it until later. The engine could have run for several minutes with the fuel in the lines, lift pump, and filters while the shut-off valve (s) are closed.

 

[Lepke]

Could be lift pump, but also air in the lines. Lack of fuel and air in the lines can give the same result. If the lift pump has a manual lever try bleeding the injector pump. The engine needs to be in a position that allows full movement of the lever. Any bubbles coming out of the injector pump means air in the lines. If so, you'll also have to bleed the injector tubes.

 

[BrianSmith]

Could be lift pump, but also air in the lines. Lack of fuel and air in the lines can give the same result. If the lift pump has a manual lever try bleeding the injector pump. The engine needs to be in a position that allows full movement of the lever. Any bubbles coming out of the injector pump means air in the lines. If so, you'll also have to bleed the injector tubes.

Ignorant question: how could air get in the lines if everything is working properly? I'm guessing I have some air in the lines NOW, with the cylinders pulling hard and some restriction in the fuel lines - but isn't it really the cause of the restriction that I need to find and fix? (Then bleed, probably.)

 

[Comodave]

Did you say that you changed the on engine filter about 3 running hours ago? If so that could be the source of air getting into the fuel system. I always ask myself what did I do that changed things? Maybe a gasket not seated properly. KISS, check the easy stuff first and whatever you changed.

 

[High Wire]

It’s either air in the injection pump from a filter gasket leak, the fuel path is blocked or the lift pump is not working. Do a full system bleed. If the lift pump puts out solid streams then it’s not the pump or blockage.

 

[Lepke]

Ignorant question: how could air get in the lines if everything is working properly? I'm guessing I have some air in the lines NOW, with the cylinders pulling hard and some restriction in the fuel lines - but isn't it really the cause of the restriction that I need to find and fix? (Then bleed, probably.)

It's an intermittent problem. The engine runs fine and then doesn't run fine. I've seen fuel lines rub a hole and vibration sometimes covers the hole and later exposes the hole. Also the filter gasket can leak intermittently. Maybe heat related. As the engine or engineroom warms, filters can expand the filter gasket gap. Heat can expand clearances in fittings.

You need to verify and locate any restriction. On difficult to find leaks, I sometimes apply air pressure to the fuel lines and get someone with good hearing to listen for leaks. If the fuel tank pick up tube can be removed, look for a screen on the bottom and remove it. Common problem with pick up tubes and screens is debris is caught by the screen and reduces or stops fuel flow. The engine stops, suction stops and reverses the fuel flow enough to dislodge the debris for next time. You don't need a screen in the pick up tube. The primary is where you want to catch it, so it's obvious on your vacuum gauge or when you change the filter element.

 

[Portage_Bay]

It's been my experience Isuzus are intolerant of air. The slightest bit will stop them. You've probably got a manual priming pump on the system and bleed points. Crack the bleed points and work the pump. Any bubbles at all will be too much air.

When you last changed the Racor did you put new seals in the cover and on the "T" handle? Having fought the battle you're loosing I change the seals every filter change. When you changed the on engine filter did you lube the seal? Putting it on dry can distort it. Lubed seal or not I suggest changing the on engine filter, if I read your post correctly it's the last thing you did prior to the problems. I have had the on engine filter seal fail after a very short time.

From the symptoms you describe it's not likely an on-engine problem other than the on engine filter. I'd start at the tank to check the fuel lines all the way to the lift pump. I do the finger wipe test at each junction and any place the lines pass through a bulkhead or are against any hard surface without chafing protection. Any fuel smell or dampness is a leak no matter how minor. Maybe even wrap each place in a white cloth rag and check again after a day or more for very minor leaks.

I use my nose as well. If I smell diesel I've got a leak. The slightest whiff of diesel will send me looking for leaks.

 

[kchace]

Ignorant question: how could air get in the lines if everything is working properly? I'm guessing I have some air in the lines NOW, with the cylinders pulling hard and some restriction in the fuel lines - but isn't it really the cause of the restriction that I need to find and fix? (Then bleed, probably.)

I think Lepke gave you about as good a suggestion as you'll find anywhere. Air can get in the lines anytime from any one of the many many joints and gaskets that make up the fuel system. You do not need a restriction, you just need an extremely tiny gap somewhere.

Ken

 

[C lectric]

Just some suggestions, not all are mine of course, but what I've gleaned from many sources, especially B.D. Forum and here.

--any fuel leak can also allow air to be pulled into the fuel system when the engine is running. Air is easier to pull than fuel. Those same not quite good enough connections may allow air in without leaking fuel.

--use the blue Scot shop paper towels and wrap fittings with some. These towels will show a distinct colour change when wetted that a white towel will not. I have even laid those towels on the area just below some fittings to check for drips that are not present while I am examining.
Also wipe those fittings and examine for any colour change or wetness which can indicate a leak.

-- as suggested check all valves, that they are indeed on.

-- If you have gate valves be suspicious that you turned them the correct way. Then get rid of them as a winter project later. Also check the stem seal on gate valves. The stem between the handle and the valve body has a seal under the nut. That seal can wear and age. If they are the problem then often simply tightening the seal nut will stop air leaks.
Gate valves have also been known to lose the stem thread so fail to open the gate. I doubt the thread loss in this case but just be aware it can happen.

-- go around and tighten all hose clamps. Don't crank on them but they should be snug.

--any signs of cracking in the hose sheath may indicate a problem that can allow air in.

--use a piece of clear vinyl tubing to check for bubbles. Insert the tubing into the fuel line just after the fuel filter as a start. There will be some bubbles at first but if all is well they should disappear quickly especially if you have purged the system properly. If they don't quit then something before the filter or the filter itself is leaking.

--move the tubing upstream towards the tank and do the same. When the bubbles stop the last item is the problem.

-- if need be use the tubing after the lift pump. They have been known to leak at the little hand pumps.

--Racors themselves have been known to cause trouble. THere is a check valve seal that must be installed in a particular orientation. The print indication can easily be missed resulting in the washer installed backwards. It matters. No, I don't have one but it has come up not infrequently.

--fuel filter seals, all of them, damaged, too old or out of place. O rings do take a set or a shape that does not always reconfigure to a new location when reused.
Improper installation of seals allowing them to pinch or roll out of place as installed. Failure to lube those seals can cause that. Have you rechecked the on engine filter bolts for tightness? Don't crank 'em but check for snugness.


I'm sure I've missed something.
Uh , last but not least but as others have reminded what was the last job you were doing near the engine? Missed something, heavy foot, didn't snug something?

 

[FF]

Not knowing where the problem is a simple method is an outboard 6 gal fuel tank full of diesel with a bukb squeeze pump.

Hook it to the engine at the fuel intake , just before the on engine filter and go for a ride.

If all is well hook it to the tank out feed and pump up pressure and watch for drips of fuel.

 

[BrianSmith]

You didn't mention it but are you sure that all fuel valves and return valves are open? I have bumped mine closed while working around the engines and not realized it until later. The engine could have run for several minutes with the fuel in the lines, lift pump, and filters while the shut-off valve (s) are closed.

I check that as part of my pre-departure checklist, and it was the first thing I checked after the engine died. The valves are all set to pull fuel from a full tank, and return it to that tank. When I next try to start it, I'll open all four tank valves, to eliminate the possibility of a clog in that tank's line. However, if that were the problem, I'm almost certain the vacuum gauge on the Racor would be showing vacuum, and it didn't move a micron from the bottom of the gauge reading. It has the "telltale" needle, so I know.

 

[BrianSmith]

Did you say that you changed the on engine filter about 3 running hours ago? If so that could be the source of air getting into the fuel system. I always ask myself what did I do that changed things? Maybe a gasket not seated properly. KISS, check the easy stuff first and whatever you changed.

Yes, about three hours ago. I didn't think of a bad seal at the gasket, so I'll check that. But I completely filled the new filter when I changed it, and since then, the engine ran perfect for about three hours. However, I suppose in that three hours, it could have been sucking in small amounts of air, and that air may have made some pockets in the lines while I was gone for the month, then those pockets of air killed the engine. Checking that gasket and bleeding the lines should resolve that, if that's the problem.

 

[BrianSmith]

It's been my experience Isuzus are intolerant of air. The slightest bit will stop them. You've probably got a manual priming pump on the system and bleed points. Crack the bleed points and work the pump. Any bubbles at all will be too much air.

When you last changed the Racor did you put new seals in the cover and on the "T" handle? Having fought the battle you're loosing I change the seals every filter change. When you changed the on engine filter did you lube the seal? Putting it on dry can distort it. Lubed seal or not I suggest changing the on engine filter, if I read your post correctly it's the last thing you did prior to the problems. I have had the on engine filter seal fail after a very short time.

From the symptoms you describe it's not likely an on-engine problem other than the on engine filter. I'd start at the tank to check the fuel lines all the way to the lift pump. I do the finger wipe test at each junction and any place the lines pass through a bulkhead or are against any hard surface without chafing protection. Any fuel smell or dampness is a leak no matter how minor. Maybe even wrap each place in a white cloth rag and check again after a day or more for very minor leaks.

I use my nose as well. If I smell diesel I've got a leak. The slightest whiff of diesel will send me looking for leaks.

Yes, the on-engine filter was the last thing I did that involved the fuel system.

Yes, I always change the two gaskets when I change the Racor filter, and I always lube the gasket on any spin-on filter.

I will change the on-engine filter, paying particular attention to the gasket of the old one, and the new one. Then I'll bleed any and all bleed screws in the system. Hopefully that'll do it. I'm almost sure I don't have a fuel leak in any hose, as the entire hose is visible except for a short section that runs under some flooring, and I think I'd smell that. But I'll check it all.

 

[BrianSmith]

Thanks for all the suggestions, including the ones I didn't reply to specifically. I've decided to put this on hold until our visitor is off the boat on Wednesday, so I won't be doing any of this until then, but I'll certainly post an update here when the issue is identified.

I love TrawlerForum!

 

[FF]

Folks with offshore visions might contemplate reworking the fuel system to include a gravity feed day tank.

A dripping leak is easier to locate than an air leak, and probably wont shut down the engine.

 

[jsplichal2]

Probably not the issue, but maybe will help someone at some point. I spent months tracking down a small air leak in my fuel line. I had changed the engine mounted fuel filters recently and assumed that was the issue, but it was not. As the problem got worse, I eventually noticed a very slow drip coming from the lift pump area. Turns out in order to fix the leak all I had to do was tighten the brass fitting between the fuel line and the pump. Food for thought.

 

[BrianSmith]

Minor update: I finally was able to start tackling the problem yesterday, and found several bits of evidence that lead me to believe that the lift pump has failed. (Mainly the fact that when I pumped the manual bleed pump part of it, fuel came out of the plunger. It's a diaphragm pump, so to me, a leak means a torn diaphragm.) I replaced it, but by the time I got that far, I was too pooped to actually test it. I should know if that was the problem sometime today.

 

[BrianSmith]

Update: hopefully the final update. Tested the new lift pump today and after about 15 seconds of some rough running, the fuel pump exploded and sent fuel everywhere, which caught fire, and within minutes, the boat was engulfed in flames. I barely escaped with my eyebrows!

Just kidding! After about 15 seconds of rough running, it smoothed out and started purring like the kitten it has always been. A few hours later, I started it again, let it warm up, ran the throttle up to higher than cruise RPM for 30 seconds or so, a couple of times, and it never missed a beat.

I guess Occam was right - if you're not getting enough fuel, maybe it's the fuel pump!

Thanks again for all the great input. It helped me focus my troubleshooting yesterday so that I was able to zero in on the pump without even trying anything else first.

 

[Comodave]

Sounds great. Usually, not always, the simple things fix it. We just have to reign in our impulse that says it must be a catastrophic problem. Glad you figured it out.

 

[rgano]

Yep, those exploding fuel pumps can ruin your entire day!

 

[g.hooker]

Thanks to all you Captains/Mechanics for a very, very helpful string of information. My understanding of a diesel fuel system's components and potential problems was nicely enhanced. Great minds! Great communicators!!

 

[dutch-barge]

Ignorant question: how could air get in the lines if everything is working properly? I'm guessing I have some air in the lines NOW, with the cylinders pulling hard and some restriction in the fuel lines - but isn't it really the cause of the restriction that I need to find and fix? (Then bleed, probably.)

Quite easily....Lehman Ford

Had a new fuel tank constructed, new flea lines, some flexible, some fixed pipe. Got the engine and all went smooth..then 30 minutes later...engine stops....tried restarting...NO luck ..Tried the manual fuel pump....No luck.
Got towed back and with a vacuum pump we got the fuel running.
So we thought ..OK must have been when we connected a diesel furnace to the fuel tank line...

Stayed on the dock, kept the engine running for a while....took the boat out 2 hrs and again.... silence ......engine stopped.... so inspection of the fuel lines....looked that one of the connection (on a longer solid pipe caused some air to be sucked) got a tad loosed because of the vibrations ...so we corrected it by making sure the fuel lines could NOT vibrate...

 

[Gypsyjon]

I had the exact same problem with a Yanmar 6UTE. After jumping all the hoops I finally had the fuel tanks cleaned and the fuel polished, problem solved.

 

[Kit_L]

FF's suggestion re. offshore aspirants might think about a gravity-fed day tank is pure gold. Such a practical suggestion. I have seen fuel lines and valving that would take a post-graduate degree in logic to figure out how to use, and every join is a potential fail point. In my next boat, I will be implementing the simplest possible systems that actually do the job. Gravity is not going to fail any time soon. Thanks FF!

 

[GoneFarrell]

Good to read it's purring normally again!

Can you say who you like to use for Isuzu parts? I run a DA-120. Thanks!

 

[kc6pyh]

Had a similar problem

Hi, I'm new to the site but had a similar diesel cutting out problem. Have you checked the air bleeder to the diesel tank. Mine was on a sailboat and near the backstay. A lot of varnish from many coats had accumulated and just filled up the tiny bleeder hole. Good Luck. Hope it turns out to be that simple.

 

[thataway]

On my diesels I always put an electric fuel pump before the first Racor. It saved my bacon several times. You can always kick it on, and get the engine running by a quick bleed. A ruptured lift pump diaphragm, can allow diesel into the engine oil--so you need to check that. It may have been leaking a small amount for some time.

I have also found air leaks in the top fitted pick up tube inside the tank. Another time I found I had had enough teflon tape that a small amount had closed the fuel line input to a Racor.

It is good to have parallel fuel filtration systems, then you can change out filters on the fly if necessary. Also as others noted, tanks which are standing for some time, get churned up, and fuel debris plugs filters when in weather which gives fuel agitation.

 

[BrianSmith]

Good to read it's purring normally again!

Can you say who you like to use for Isuzu parts? I run a DA-120. Thanks!

I've bought all of my Isuzu-specific spares from Logan Diesel (logandiesel@sbcglobal.net) - Sally Logan. But that was about 3 years ago. You can email Sally at logandiesel@sbcglobal.net.

 

[Tangler]

My Lehman’s had the same problem. Air was apparent as the last filter in the 3 filter system had no fuel in it when I got priming for a restart...I changed the lift pumps which did not solve the problem. American Diesel told me to change the fittings that go to the lift pumps with a couple of special ones they sent me...that did it. There was more to it than I describe but essentially They knew exactly what the problem was when I described it too them and the solution. Try talking directly to the source or a good mechanic.