Problems with bad fuel

[oldjags]

I went and let some water get in my fuel tank - either condensation from a tank that wasn't full, or maybe the tank fill o-ring has a leak. :-(

Regardless of how it got in there, it brought those little critters that gum up the fuel lines. We were motoring, and had a sudden loss of rpm from 2200 down to around 1200, and it would surge up and down. The engine never died, but we had to limp in at low rpm to keep it running steady.

So I completely removed the Racor (full of water and gunk) and cleaned it, and replaced both fuel filters. I removed the fuel gauge and vacuumed out the tank. I removed the fuel pick-up from the tank and made sure it was clear. I made sure the line from the tank to the Racor was clear.

But I'm still having the same issue. The engine runs fine at idle. It runs fine for at least 20 minutes at 2500 rpm, with no load. But it only runs fine in gear for 10-15 minutes. Then the rpms will drop to 1500 or so for 10-15 seconds. Then it will pick back up but continue to act up for a few minutes. Then maybe it will run fine for another 5-10 minutes.

I keep thinking I have air in the line somewhere, and that it will eventually work its way out of the system, but we went out today on a test run for an hour and it didn't get any better.

Should I change the filters again? Other suggestions?

[belizesailor]

Given that you just changed the filters, probably not a dirty filter. Air in the fuel system and a clogged filter can present similar symptoms (the surging RPMs you experienced). You dont mention it, but you did bleed the system right?

This is also where a vaccum gauge comes in handy...it would make it immediately obvious whether it was a clogged filter or not.

Is there any water in the fuel water separator on the Racor?

Another possibility is a vaccum leak...if something didnt quite seal right after the work you did. Also can present silimar symptoms...and can be a bitch to detect.

My suggestion: try bleeding the system again. If still have the problem, then take another look at the primary filter. If the fuel is really dirty then you could have clogged another filter, but I suspect its air. If the system is bled thuroughly and the filters look good...then its on to the vaccum leak.

[oldjags]

I did bleed the system after forgetting to do it the first time when I changed the filters. It started right up and ran for a minute, and then died.

So I got the Yanmar manual out and went through the bleeding procedures and then it started right up again. But there could still be air in there, I suppose. Any air on the pressure side of the fuel pump should get purged out pretty quickly, shouldn't it?

And, any air leak would have to be on the suction or tank side of the pump, wouldn't it? Probably the Racor would be the first suspect, since I took it apart and cleaned it. So maybe one of the fittings is letting air in. I'll recheck them and see if that helps.

[Uncle Bob]

Also worth checking all the fuel lines, sometimes the gunk that clogged the filter will restrict the lines as well. Don't ask me how I know.

[travellerw]

Originally Posted by oldjags

I did bleed the system after forgetting to do it the first time when I changed the filters. It started right up and ran for a minute, and then died.

So I got the Yanmar manual out and went through the bleeding procedures and then it started right up again. But there could still be air in there, I suppose. Any air on the pressure side of the fuel pump should get purged out pretty quickly, shouldn't it?

And, any air leak would have to be on the suction or tank side of the pump, wouldn't it? Probably the Racor would be the first suspect, since I took it apart and cleaned it. So maybe one of the fittings is letting air in. I'll recheck them and see if that helps.

No any air is long gone. The amount of fuel a diesel engine circulates would flush the air in the line out very quickly once the motor is running. The only way there is still air in the system is if there is an air leak on the suction side of the pump. Check all your pipe clamps.

Personally I think you probably have some gunk still in the fuel line that is working its way through. Shine a light at your racor and see if you see anything. Big crap will spin out and be in the bottom of the bowl. We have known other boats that required 4 filter changes before getting all the gunk out (however, they didn't vacumm the tank).

[belizesailor]

Originally Posted by oldjags

I did bleed the system after forgetting to do it the first time when I changed the filters. It started right up and ran for a minute, and then died.

So I got the Yanmar manual out and went through the bleeding procedures and then it started right up again. But there could still be air in there, I suppose. Any air on the pressure side of the fuel pump should get purged out pretty quickly, shouldn't it?

And, any air leak would have to be on the suction or tank side of the pump, wouldn't it? Probably the Racor would be the first suspect, since I took it apart and cleaned it. So maybe one of the fittings is letting air in. I'll recheck them and see if that helps.

Yes, air on the pressure side, assuming direct return line to tank (its uncommon, but I have seen recirculating return lines), should be long gone.

Yes, vaccum leak would be on the suction side of the system...between lift pump and tank. Most likely suspect is where you just worked: the Racor, etc. Might as well crack it open and inspect filter to see if it clogged. Replace o-rings and carefully reassemble...maybe you will get lucky. Ditto on any other fittings you messed with.

Re debri in lines, thats another possiblity...you could purge fuel lines with compressed air. I assume copper/metal lines from tank to near motor and then some type of flexible line to motor?

[Paul L]

Make sure your tank vent is clear. You can open the fuel cap and run engine to see if that is the issue.

[TeddyDiver]

Sometimes the gunk will sit fast in the fuel lines not even compressed air helps and don't ask how I know Small wire run through the fuel line from the tank to the first filter and a pipe brush is what might work. Any T's on the way must be opened. Other than that is to chance the fuel pipes and hoses open all joints and scrape the crap away..

Teddy

[sailormed]

Changing the Racor filter is not enough.
I had similar problems and the obstruction was IN the Racor housing. Fuel enters horizontal and then takes a bend to go down to the outside of the filter. There was gunk in this 90° bend!
So lines are clean, filters are clean, pickup tube clean but NOT the lines in the Racor itself!
Lesson learned.
To be honest I did not find this myself, but an old diesel mechanic on the island of Ponza on a Sunday evening. The bill was stiff.

[belizesailor]

Originally Posted by sailormed

Changing the Racor filter is not enough.
I had similar problems and the obstruction was IN the Racor housing. Fuel enters horizontal and then takes a bend to go down to the outside of the filter. There was gunk in this 90° bend!
So lines are clean, filters are clean, pickup tube clean but NOT the lines in the Racor itself!
Lesson learned.
To be honest I did not find this myself, but an old diesel mechanic on the island of Ponza on a Sunday evening. The bill was stiff.

Thats because it included tuition. [emoji6]

[shakey doug]

Take a look at lift pump, possible full of gunk or valve not seating due to rubbish. No engine Model given to be more specific.

[belizesailor]

Could be another possibility.

While you are at it...check oil level to be sure its not rising...which can be caused by a lift pump diaphram failure.

[boat driver]

three thoughts-
i did not see the type of engine-

check the return line to be sure flowing- it is smaller diameter and often has a check valve <3psi either at the engine or at the tank- the purpose is to keep the system full when the engine is shut down-

2) as mentioned try with tank cap off and see if vent is clogged as well? since issue happened prior to filter changing also check fuel pump itself for crap stuck-

3) get some Fuel Right (fuelright.com) and shock the tank. It will kill and emulsify anything in the system and pass it into the filters. Be prepared to change primary filters a number of times if tanks are dirty. Fuel Right has few competitors and a track record of cleaning systems. It is a bit more expensive but well worth it. I believe a 300 gallon shock is $25. It will not help biodiesel sludge though- that is only fixed with a hot fuel tank cleaning. (save the environment in as many ways as possible but do not use biodiesel in a marine application unless burning lots of fuel in short times. it grows like the weeds in a garden.)
good luck .

[oldjags]

The engine is a small Yanmar 3HM35F. The fuel line from the tank to the Racor is rubber fuel hose, and I blew through it by mouth from the tank end and spewed diesel all over the sole, so I know it's clear!

I do think the problem is probably in the Racor - maybe an obstruction internally as has been suggested. When I unscrewed the top of the Racor yesterday, I could feel a small amount of vacuum inside as I took the cover off. Since the fuel from the tank to the Racor is a siphon gravity feed, there shouldn't be any vacuum inside the Racor, I don't believe.

Thanks for all the clues. I'm back at it today to see what happens!

[Siberian Sea]

If when you remove the top of your racor you find the filter is under a vacuum then without doubt you have an abstraction in the fuel system and it’s located between the filter and the end of the pickup tube. The only other possible problem would be the tank breather vent. Many racors also have an internal ball check valve. It’s a small plastic marble sized ball that is located inside the housing just above the filter. You cannot see this valve unless you take the unit appart. Mine once had junk plugging the ball from moving and it restricted fuel flow. This restriction would cause my fuel system to come under vacuum the engine ran and the injection pump was powerful enough to even suck small amounts of air past the o ring seals.
Anyway remove the fuel line on the tank side of the racor and blow through it and listen for air bubbles in you fuel tank. This will let you know if it’s a clear path, then reconnect, bleed the system and start engine.