Intermittent PRM bog down

[c130king]

M25XPB. 2500 hours. Last couple of weeks having an issue where motoring at just about any RPM the motor will start to choke/bog down. RPM will drop down below 1000 (to like 400 sometimes) and run "rough" and then sometimes it will go back to normal after a few seconds and sometimes the motor will shut down.

Sometimes if I can pop it into neutral quickly and push up the throttle it will recover. But sometimes not. I have gotten it to do this while tied up to the pier with transmission in neutral.

Replaced fuel filters (+ oil + transmission...it was time anyways) yesterday. Bled air out of the fuel lines using the bleed screw. But it still kept happening.

Engine would always restart if it did quit.

Took some folks out last night and was considering cancelling as the motor was doing this yesterday afternoon. But then about an hour prior the motor seemed to run fine for 15-20 minutes. So we went...weather was excellent so no concerns about weather. Motor ran great for 2 hours...almost no wind.

I use the boat just about every day. Fuel does get used and marina has nice ValveTech Diesel.

I looked at the oil pressure sender and it looks like the wires are attached properly. But that is what I am thinking the issue is. Maybe bad lift pump (or whatever it is called).

Could it be fuel tank vent and tank is vacuum locking up?

Any other thoughts on this? Appreciate any insights/comments/thoughts.

Cheers,
Jim

 

[SawyerCurt]

Sounds like you are having the same problem I was having a couple of months ago, and it turned out to be the fuel pump connection. Here is the link to my original post, all the advice I received, and pictures of the connection that turned out to be the problem. http://forums.catalina.sailboatowners.com/showthread.php?t=165656

 

[Stu Jackson]

Things to check

1. I looked at the oil pressure sender and it looks like the wires are attached properly. But that is what I am thinking the issue is.

2. Maybe bad lift pump (or whatever it is called).

3. Could it be fuel tank vent and tank is vacuum locking up?

4. Any other thoughts on this? Appreciate any insights/comments/thoughts.

Jim,

1. Probably not since it has nothing to do with the fuel.

2. Could be, and could be either a bad connection/ground, filter needs to be cleaned, or it's plumbed wrong (should be after the Racor primary).

3. Could be. Could also be the fuel pickup screen inside the tank if it hasn't been removed.

4. Yes: Critical Upgrades http://c34.org/bbs/index.php/topic,5078.0.html Includes a lot of these items and more which apply to your engine.

 

[c130king]

Thanks guys. Will do some more reading. Just frustrating because of the randomness of the issue.

Cheers,
Jim

 

[centerline]

Thanks guys. Will do some more reading. Just frustrating because of the randomness of the issue.

Cheers,
Jim

as others have said... it could be one or more of the issues stated below.
after the filter change and it still happens, I would inspect each in the following order.

-lift pump weak
(when bleeding the system, with the bleed screw open a half turn more than normal for bleeding, you should be able to get a good strong pulse of fuel with each stroke of the pump lever. keep a rag over it because if it is putting out the pressure and volume like it should, it will spray the engine compartment.. if its is weak or not much volume, the lift pump is bad)
also check the weep hole on the lift pump, if it has any sign of moisture, it will be a sign of a failing diaphram within the pump, and could actually suck a bit of air there.

-loose hose connection BETWEEN THE TANK AND THE LIFT PUMP, allowing air to be sucked in to the line
(if this is happening you should notice a bit of air at the filter bleed screw if you shut down a bleed after noticing it bogging)

-another hidden filter/screen in the line somewhere, or the tank pickup screen plugged
(fuel algae can even plug a fairly coarse screen, the one in the tank is fine and is easily plugged by normal debris)

-an old fuel line that has collapsed and restricting the normal fuel flow...

there is not much else that would cause it to repeatedly bog, then run fine, so im confident you will find the problem within the above areas....

 

[Stu Jackson]

M25XPB bleeding

-lift pump weak
(when bleeding the system, with the bleed screw open a half turn more than normal for bleeding, you should be able to get a good strong pulse of fuel with each stroke of the pump lever. keep a rag over it because if it is putting out the pressure and volume like it should, it will spray the engine compartment.. if its is weak or not much volume, the lift pump is bad)
also check the weep hole on the lift pump, if it has any sign of moisture, it will be a sign of a failing diaphram within the pump, and could actually suck a bit of air there.

Good advice, otherwise, BUT the M25 series engines have bleed screws (the knurled knob) and diesel fuel does NOT and should not ever flow out of them.

"...it will spray the engine compartment..." should never happen.

On some engines this could happen, but not on your M25XPB. It's really important to be ENGINE-SPECIFIC in answering these types of questions. For example, I know little to nothing about Yanmar engines, so I stay away from answering questions about those, except for general symptomatic issues, exhaust elbows the Yanmar skippers jump right on anyway, and alternator questions.

 

[centerline]

Good advice, otherwise, BUT the M25 series engines have bleed screws (the knurled knob) and diesel fuel does NOT and should not ever flow out of them.

"...it will spray the engine compartment..." should never happen.

On some engines this could happen, but not on your M25XPB. It's really important to be ENGINE-SPECIFIC in answering these types of questions. For example, I know little to nothing about Yanmar engines, so I stay away from answering questions about those, except for general symptomatic issues, exhaust elbows the Yanmar skippers jump right on anyway, and alternator questions.

You are absolutely right that its more helpful if someone who knows the specific engine intimately, answers the question with a full and clear description of what to for. But in the mean time maybe what we offer can help..
(The same could be said for many other topics posted

The OP said he bled the air out of the system with the bleed screw, so I can only assume he has a bleed screw..

and even though i dont know about the m25 specfically, I do know fuel systems in general very well... and if i was there to see what the OP was dealing with, I would then know exactly what to do, as there arent too many different setups for fuel delivery...

so, in an attempt to be helpful, all any of us can do is give the best of what we know from the information that we have and hope the someone can gain some bit of helpful information from it.... and if it is not helpful, then one only has to read the next post in line.

And yes, spraying the engine compartment with fuel is NOT something we should do, but if the lift pump has the 18-28 psi that it should have, it would definitley be able to happen... my point was that the lift pump needs pressure and if it doesnt have it, its either bad, or it isnt getting fuel to it... and could be the problem.

 

[c130king]

Yes, I have a bleed screw. After changing the fuel filters (both of them) I open the bleed valve and start pumping the manual pump handle on top of the primary fuel filter. Fuel starts to fill the primary filter and water separator bowl. Then the fuel flows to the secondary filter. Air/fuel bubbles will bubble out of the bleed valve. But after a few minutes of pumping I get a good steady stream/spray of diesel. And yes it goes over the engine...at least on the starboard side...and onto the cabin sole next to the engine.

I have not used the lift pump to do this before...but I have read on here about it. I always change the filters solo so it seems easier to just use the manual pump. It only takes a couple of minutes.

However, I think Centerline is on the right track. My buddy who normally helps me out with engine issues also said he thinks the problem is up stream of the lift pump. Probably a cracked fuel line or hose clamp allowing the pump to suck in some air which passes through to the injectors causing the RPM drop off.

The intermittent factor has to do with motion or vibration.

Going to see what I can find on that issue. Lift pump is less than a year old.

Appreciate the comments/help.

Cheers,
Jim

 

[centerline]

upstream of the lift pump would mean towards the tank, and if there is a leaky fitting, it will not show as a leak because of the suction of the lift pump.... and dont rule out the lift pump just because its only a year old.
as unlikely as it may be, its only a mechanical device and it could be faulty.

so the filter base has the primer pump on it, which could mean that the lift pump does not have one, although some still do.
but either way, as much fuel as you have when bleeding the system using the filter base pump, if you open the same bleed screw with the engine running, you should have more fuel and more pressure available there at the bleeder that is now being pushed by the lift pump.... if it has weak flow or low volume, you either have a weak lift pump or a restriction/suction leak upstream towards the tank.

make sure the hose is in good condition, all threaded fittings have sealer on them, all fitting nuts are tight, all clamps are snug (any signs of cracking or damage of any kind at the clamps, and the hose should be cut back an inch and reattached), and that there isnt an inline filter somewhere near the tank that has clogged.... after doing a thorough and complete inspection of all that and it still doesnt solve the problem, check the pick up in the tank.

also, just for the fun of it, check the fluid levels in the gearbox(s).... we had a powerboat come in once that had a surging issue, the description was like a fuel problem... it turned out to be a dry gearbox.

 

[Stu Jackson]

Yes, I have a bleed screw. After changing the fuel filters (both of them) I open the bleed valve and start pumping the manual pump handle on top of the primary fuel filter. Fuel starts to fill the primary filter and water separator bowl. Then the fuel flows to the secondary filter. Air/fuel bubbles will bubble out of the bleed valve. But after a few minutes of pumping I get a good steady stream/spray of diesel. And yes it goes over the engine...at least on the starboard side...and onto the cabin sole next to the engine.

I am confused about fuel spilling out. I am under the impression that the knurled knob on the injection pump doesn't let any fuel out. Perhaps you are talking about fuel coming out of the top of the Racor vent. You can avoid this by using the lift pump.

Here's a discussion about how your boat is most likely (only you'll know for sure) wired: pump comes on when glow plugs are engaged (not when the key switch is just ON) AND when the oil pressure comes up after the engien starts running.

Good luck. A bunch of reading, but worth it to find out how stuff works.

http://c34.org/bbs/index.php/topic,5078.msg41829.html#msg41829

 

[c130king]

There is a bleed valve (knurled nut) near the injector pump. Open the nut a few turns to expose a hole in it. As you pump the handle on top of the Racor fuel/air bubbles out but eventually all the air is pushed out of the lines and fuel filters and fuel will spray out. Quickly screw the nut back down tight. A little fuel spray will need to be wiped up. I guess one could hold a rag there and catch most of it. But I am not that smart.

Cheers,
Jim

 

[c130king]

And I do understand about lift pump working with key in "glow plug" position and then will run when the oil pressure switch keeps it running with oil pressure.

I guess the theory is that if the oil pressure drops then fuel pump will stop running and the engine will stop before too much damage occur.

That is why I suspected oil pressure sender and/or connections. But now I suspect air leak up stream of the fuel pump and it sucks air/cavitates or something like that.

Will keep investigating.

Cheers,
Jim

 

[RichH]

Your symptoms are consistent with an air leak or blockage in the fuel lines.

Id recommend that that you:
1. install a vacuum gage either ON the 'secondary' Racor (on its 'outlet' side) ... What I mean by 'secondary' is: Fuel Tank --> primary filter ---> SECONDARY filter ---> engine mounted 'guard filter' ---> engine lift pump.
2. Reinstall NEW gaskets/Orings on all fuel filters that you recently changed, and use fuel oil to 'lubricate' the new o-rings/gaskets when reinstalling.
3. check all tube connection fittings for small cracks.

With the vacuum gage installed and the engine 'stumbles', note if the vacuum reading on the gage is 'high vacuum' (blockage in the fuel delivery system, including a 'crudded up' filter) or 'Low' - indicating an air leak.

After you find out your 'fuel problem or air leak problem' and fix it ..... To establish the maximum vacuum value at which the engine will stumble ... with the engine running near wide open throttle and trans in forward, have an assistant slowly close the tank valve & watch the vacuum increase on the gage and note where the engine begins to stumble ... immediately open the tank valve. This will be your maximum vacuum value at wide open throttle. Multiply that number by .8 - this will be your 'change out' value for your filters.

If with 'clean/new' filters & the system at near WOT remains high vacuum .... check all the hose/tube for obstruction or debris (fungus or bacteria 'wads') between the filters and the tank .... including the 'teeny screen' at the entrance of the 'dip tube' inside the tank.
If with clean/new filters and with new Orings etc. installed, the engine a near WOT, and with a LOWER than normal vacuum reading - check for air leaks. This includes scrutinizing especially the 'nuts' on all compression fittings for cracks, etc.
Normal reading (for future reference) is developed by recording history of fuel system vacuum value of the engine running at 'cruising rpm' (with new/clean filters.)

 

[malcs2010]

I had a similar problem with a Hunter 41AC. I finally chased it down to be a booked filter on the fuel pick up in the tank. There is a fine wire filter on the Hunter tank pick ups and mine was blocked with goop and this effectively starved the engine. I caught on to it as my tank was filled with pink foam from the fuel being foamed in the fuel pump and injection pump. See my post on Fuel starvation dated 27/10/2014. Cleaned out the wire filter, dosed up the tanks with fuel conditioner as I did not want to have to clean out the tank - (lazy but no easy inspection hatch and tank full of fuel) and off I went. If you still think it is an air leak, try putting in a piece of clear plastic hose into the fuel line and look for bubbles. If bubbles look ahead of the clear plastic. If no bubbles - no problem. Obviously enough, start at the fuel pump end and work back towards the tank.
Good luck, but check the fuel pick up.