Low engine RPMs >> Bad Fuel/Filter?

[CowboyWay]

I'm new to servicing the fuel system and have read a fair bit on the topic, but had a problem recently that I think is fuel related and want to confirm. We left for a 4 hour trip that was going to require motoring most of the way due to the winds. Engine seemed fine the first 20 minutes out of the harbor, then while motoring at 1/2 throttle the engine started stalling. RPM dropped from 2500 or so down to 1000 or less. Moving the throttle more open had no effect. At time the engine sounded like it was going to completely die. This went on for a a few minutes. I'll note the there pretty good swells causing us to toss around in the direction we were headed. We got a tow back to the marina where we started to figure things out. The engine Universal M25XPB has never had this issue in the past that I've seen.
Diagnosing things, the fuel pump seemed to be working. If I opened a bleed valve on the engine, fuel would come out with it on. However, the water separator drain valve seemed blocked. I loosened it a few turns but would only get a drip out of it? Another pic shows green slime in the bottom of the bowl. Uh oh I thought. The filters have not been replaced in the past few years, but I do have replacement on hand. This was probably the first season where the boat had a 3/4 full (or so) tank over the winter season instead of full. I'm thinking that led to issue.

Do you agree and if so what's a proper procedure to clean up the system? Also, I can't tell from the pic of water is in the bowl?

 

[Stu Jackson]

Fuel Starvation and The Obscure Check Ball Valve
Fuel Starvation and The Obscure Check Ball Valve
and
Fuel Starvation and The Obscure Ball Check Valve

 

[Tally Ho]

After reading Stu’s notes about the check valve, I would replace the fuel filter (not familiar with the canister type…can you see how plugged up it is?)….

If you have an inspection port in the fuel tank, I would open it up and get a look in the tank to see if you have a bunch of junk in there.

Some people have had problems with a screen over the fuel pickup tube, and getting junk it the screen (particularly in conditions you described where any gunk in the tank gets stirred up). Solution there is to pull the dip tube and remove or clean the screen.

I inspected my filter this week before filling the tank... I motored in some bouncy seas last week but had no motor issues. I don’t have an inspection port, so about all I could do was pull the filter and see what it looked like..a bit brown, but it is about 5 years old. I reinstalled the filter, filled the tank, and ordered a new Filter to have on hand (I thought I had a spare, but when I opened it, not the right one )

Greg

 

[JoeWhite]

Here is my experience. I hope it helps you.

Fuel Starvation | Sail La Vie

mei1970.org

 

[capta]

Before getting too deeply involved in the fuel system, on a lark, check that the throttle cable has not worked its way loose, at either end.

 

[CowboyWay]

I was unaware of the check ball assembly on the primary fuel filter, but I do see the slotted screw-type cap on top of mine in the same place.

So I'm thinking:
shutoff fuel at tank
remove primary filter bowl and filter, clean the bowl and replace with a new filter
clean out that check valve
replace the secondary fuel filter mounted under the engine
reopen the tank shutoff valve and bleed the system at the point after the secondary filter
confirm the throttle cable is securely tightened

I'll note, my symptoms are similar to those that posted. I've also seen it where it will run at idle in neutral, but as soon as I engage the transmission, the rpm dip below 1000 rpm. So a restriction in the system seems to be the culprit. Not sure on the 310 if there is an access panel on the fuel tank, but I'll look. If I remove the intake tube from the fuel tank, what material is used to reseal that when you replace it?

Looking at the old pic I had of the tank (without the water heater installed), I see the shutoff valve there but not any way to remove screws or dip tubes?

thanks all!

 

[jssailem]

Your thinking is sensible.

"Know thy enemy", is one of the first requirements in preparing for battle.

Here is a resource... Diesel Bug 101 - What Is It? How To Avoid It

From a post I shared in January of this year.

BAD FUEL can spoil your day

Here we are in the middle of winter beginning to plan our next sailing season. Maybe we are new to using a boat with an inboard engine. Some of us have years of mechanical experience so we know. Some are facing the idea of being alone in the water with a dead engine for the first time. We...

forums.sailboatowners.com

 

[CowboyWay]

We’ll that didn’t work. I completed everything in that list above and it will only run for a minute or less and die. Didn’t find anything in the check valve. Looked pretty clean. I bled the system until the air was out. Did that at the secondary filter and at the bleed point after that filter. Weird. How do you know if your fuel pump is bad? Mine makes different clicking sounds at different pitches when starting it. Like maybe fuels flowing and then not. It’s definitely louder than it used to be.

 

[Tally Ho]

I was unaware of the check ball assembly on the primary fuel filter, but I do see the slotted screw-type cap on top of mine in the same place.

So I'm thinking:
shutoff fuel at tank
remove primary filter bowl and filter, clean the bowl and replace with a new filter
clean out that check valve
replace the secondary fuel filter mounted under the engine
reopen the tank shutoff valve and bleed the system at the point after the secondary filter
confirm the throttle cable is securely tightened

I'll note, my symptoms are similar to those that posted. I've also seen it where it will run at idle in neutral, but as soon as I engage the transmission, the rpm dip below 1000 rpm. So a restriction in the system seems to be the culprit. Not sure on the 310 if there is an access panel on the fuel tank, but I'll look. If I remove the intake tube from the fuel tank, what material is used to reseal that when you replace it?

Looking at the old pic I had of the tank (without the water heater installed), I see the shutoff valve there but not any way to remove screws or dip tubes?

thanks all!

View attachment 215433

Looks it would be tough to get the pickup tub out without moving the tank. The fitting may unscrew from the tank and the dip tube would come out with it.

but no clearance under there…

try all the other things first

Greg

 

[SycloneDriver]

Perform a fuel volume delivery test on the pump. Remove a fuel line as close to the injector pump as possible. Direct the fuel flow into a quart jar. Energize the pump and time how long it take to fill the jar 1/2 full. Should probably take 20 to 30 seconds. Also a good time to inspect the appearance of the fuel.

 

[SycloneDriver]

The Racor fuel filter appears to be on the suction side of the electric pump. This is common, I'm not really a fan of this setup. Even a small air leak on the suction side can be troublesome and difficult to find, unless the tank is above the fuel system. Your tank does appear to be above the rest of the system. Maybe an air leak at the connection to the tank or a cracked pickup tube. I have temporally used clear vinyl hose to find the source of air intrusion.

 

[Davidasailor26]

The timing test @SycloneDriver suggests is a good one. You can also listen to the sites of the clicks while running that test. The pump should probably click about once a second. Much slower than that suggests a clog, either at the pickup tube, Racor, or lift pump screen.

 

[CowboyWay]

Thanks for the tips on testing the lift pump. I'll give it a go in a few days. Another thing I'm now wondering is whether there's air in the primary racor system. When I filed the assembly up with fuel before screwing it on, the level was about 3/8" below the top. I didn't realize until now after reading a manual on the racor filters that you need to open that bleed screw and then use that primer pump to get the air out. I didn't do that. Maybe that's the cause for the changes in sounds from the lift pump just before starting the engine?

 

[Stu Jackson]

1))) but as soon as I engage the transmission, the rpm dip below 1000 rpm.

2)))) So a restriction in the system seems to be the culprit.

2)))) Noooooooooo

1)))) seems like something EXTERNAL is your problem, like a bag wrapped around your propeller. Or your transmission is toast for some reason.

 

[CowboyWay]

2)))) Noooooooooo

1)))) seems like something EXTERNAL is your problem, like a bag wrapped around your propeller. Or your transmission is toast for some reason.

It died each time yesterday without ever putting it in gear.

 

[jssailem]

Fuel starvation is a usual suspect.
Fuel, air, compression are the keys needed to make your engine run.
If it starts then air and compression are there.
If it runs and then stops, I would look at fuel.

It is a matter of checking every link from the fuel you put into the tank to the engine fuel lines.
Reading your descriptions:

1. motoring most of the way due to the winds
2. there pretty good swells
3. Engine seemed fine the first 20 minutes out of the harbor,
4. engine started stalling

It leads me to believe you stirred something up that was brewing in your tank. Somewhere in the path (tank - hoses - filters) I would look for a partial clog.

• I would start at the tank.
• Is there a something in the tank that should not be there.
• There could be a screen on the end of the dip tube used to suck fuel from the tank.
• If all is clear, I would work my way along the hose towards the engine

It is a bit tedious. My suspicion is that somewhere along the way you will find something that is partially blocking the flow of fuel to your engine.

 

[JoeWhite]

Blocked fuel hose from the fuel tank to primary filter is a possibility.
You can test this by getting a 3 gallon plastic diesel fuel container withe 2 gallons of fuel in it and connecting fuel hose to the input of the primary filter and running the engine.

 

[CowboyWay]

So I had the service shop look into the matter. It seems it might be a combination of things, but the main culprit was a bad oil pressure sender which had been replaced a few months ago as part of my request to get the low oil pressure alarm working. They couldn't do an extended engine test at the time as the boat was on the hard. Apparently that replacement sender was also bad and that combined with something about the fuel pump wiring being "wrong" were the cause. I'm aware that a second low oil pressure switch is in line with the fuel pump, but I didn't hear that the fuel pump or oil pressure switch was bad. It all seems to work just fine now and have used the boat twice since with no fuel starvation issues.

Thanks everyone for the assistance. You're all the best!

Pic of new wiring. the yellow wire is "new". I assume it goes to the oil pressure switch, but didn't look under there yet. I wonder if they ran a new wire back to the admiral control box for the oil pressure alarm? I didn't get a lot of details, but heard it took the better part of a day.