Universal M25 Diesel has "fuel system air leak"

[Tim S.]

My M25 started stalling yesterday. I thought it was the fuel or water, drained the separator and replaced fuel filter, then bled the line, and she started. Ran for 45 mins and stalled. So I bled her again, and she started and ran for 45 mins, etc. I saw small bubbles coming from base of Injector Assembly where it touches the block, so I'm thinking that might be it?

What to do? Any advice?

If it is the injector, can I just tighten it somehow, without removing it, replacing washer, etc?

 

[jssailem]

Hi Tim.
Welcome to the SBO Forum.
Thank you for the image.
What I see is dampness on the engine head. It can be oil or diesel fuel. I suspect the latter. The return line hose with the hose clamp also looks damp. I would suspect that is the source of the diesel fuel that is found on the head at the base of the injector. I would replace that length of hose. New clamps, and clean/wipe down the engine head surface so you can see if there are any more leaks.

Now for the bubbles. The injector at the base is inserted into the head at the top of the cylinder. Fuel comes out of your High Pressure Pump through the steel fuel line at the top. It is forced into the injector which meters the fuel into the cylinder. At the same time the fuel is injected, the piston in the engine is pressing up in the cylinder. The pressure rises until the diesel air mix combusts driving the piston down.

If you have bubbles from this process they would be under extreme high pressure. You may have some escaping partially combusted exhaust from a failed washer between the injector and the head. A little tightening will not resolve that nor will it address the behavior your engine is exhibiting. I would address the injectors when you do an engine service. I would not wait too long. These issues never resolve themselves.

The description of your engine running, racing, stalling then being resolved for a short time by bleeding the engine sounds like "FUEL STARVATION" . Start at the tank and follow the fuel lines to the engine. Make sure the tank is clean and the pick up tube is clean and clear. At each connection remove/clean/ replace or reconnect the hose. Clean the connections on the fuel filter. Install a clean filter. Check the pump that the connections and any filter is clean. Connect and assure that all connections are firmly tight / NOT strangling tear through the hose tight.

Bleed the system and then see if that resolves the issue.

Read about and inspect the hidden filter connection check valve that @Stu Jackson has posted here on SBO.

Clean and adequate fuel flow is what your engine wants. If this is limited or stopped the engine reacts by racing RPM's, Coughing, then stalling. It will not restart till you feed it what it wants.

Good luck.

 

[Ralph Johnstone]

Mr. @jssailem most likely has the better (and simpler) idea that you are suffering from a lack of fuel rather than the presence of air.

If your fuel supply does pass the taste test and you are then looking for air ingress, one of the first things to remember is that air requires a NEGATIVE pressure to enter the fuel system. Initially, don't bother to look at any joints AFTER your lift pump. They are all under positive pressure while the engine is running. After that, it just gets time consuming.

 

[Stu Jackson]

Read my answer to your identical question with a different title:

Possible Air leak in M25 fuel line?

My M25 started losing RPM's, recovered for a while, then stalled yesterday. I thought it was water in fuel, drained the separator, bled the line, and she started. Ran for 45 mins and stalled (again preceded by losing rpm's, and some power, some recovery, then a full stall). So I bled her again...

forums.sailboatowners.com

 

[rgranger]

Read my answer to your identical question with a different title:

Possible Air leak in M25 fuel line?

My M25 started losing RPM's, recovered for a while, then stalled yesterday. I thought it was water in fuel, drained the separator, bled the line, and she started. Ran for 45 mins and stalled (again preceded by losing rpm's, and some power, some recovery, then a full stall). So I bled her again...

forums.sailboatowners.com

Oh... and then there is this one..

A gentle reminder about duplicate threads and selling.

Folks, Just a gentle reminder about selling items in the forums. Forum rules prohibit advertising in the forums. SBO provides a free classified section for gear, a free "Digital Dumpster Dive" for items being given away, and a modestly priced classified section for boats. Please use these...

forums.sailboatowners.com

 

[Tim S.]

[B]jssailem[/B] and others, thank you. After trouble-shooting virtually everything, it came down to a built-in filter in the the fuel lift pump (which I didn't even know was there!). This explains the sporadic nature of the stall. Apparently, sometimes enough fuel would get through the clogged filter. And other times, it just became too clogged for the pump to push the fuel through the clogged filter screen. I swamped in an entirely new electric fuel pump, and she is now running fine. Thank you all again. Jsasilem's advice to begin at the fuel tank, pick up tube, etc is the right methodical approach. I used a try this, now try this, hmm maybe this approach, which took much longer to find the problem. My learning? Fuel Starvation was indeed the symptom. And there are several logical places the clog could happen (since we determined no leak early, it had to be a clog). The tank lift tube. The lift pump and its filter. the right-angle connections to water separator. The filter in the water separator. The main fuel filter. Hope this helps a future reader with similar engine symptoms!

 

[Stu Jackson]

@Tim S.

Thx for reporting back. Do you understand now why we keep saying that the fuel lift pump should be after the primary filter?

 

[Tim S.]

@Tim S.

Thx for reporting back. Do you understand now why we keep saying that the fuel lift pump should be after the primary filter?

Yes. And low and behold, they had the lift pump BEFORE the separator filter. Neither I nor the previous owner realized there was a filter inside the lift pump - which was then the FIRST filter catching debris from the fuel tank for 15 years!!!

 

[Ralph Johnstone]

Do you understand now why we keep saying that the fuel lift pump should be after the primary filter?

It filters out the loose nuts and bolts as they come down the fuel line ?

 

[odaydokay]

O'day ( at least on the 28's and probably others) plumbed tank to lift pump to engine with its screw on filter. Some of us added a Racor. No problems for me ever as I am religious about cleaning the filter (which is really just a plastic circular fine screen) with a magnet inside the cap below it. Not doing that for year after year almost has to bring an issue. Won't matter what order the filters are in.

 

[Stu Jackson]

Not doing that for year after year almost has to bring an issue. Won't matter what order the filters are in.

No, it won't. The primary (usually a Racor) will filter out way more than that stupid little screen will. Our C34 skippers have been urging boat owners to correct the flow

from the factory tank>>pump>>Racor
TO tank>>Racor>>pump

for 3 bloody decades!!! With good reason.
All 1,801 C34 hulls simply disagree with your conclusion.

Once you make the correction, there will be nothing for the pump's screen to filter. You can ignore it.

 

[Ralph Johnstone]

from the factory tank>>pump>>Racor
TO tank>>Racor>>pump

Can't quite follow your flow diagram. Can you explain to my rain sodden brain why the fuel goes from the factory tank to the pump ?

And on the next line, what does it mean when the fuel is heading back to the tank, but first goes through another Racor filter and then through some additional pump ?

Too many filters and pumps for me to follow. I guess I just don't get out enough .

 

[Stu Jackson]

Sorry, you're right. Here's the clarification:

from the factory: fuel tank>>pump>>Racor
change this TO: fuel tank>>Racor>>pump

A : goes a long way these daze...

 

[Ralph Johnstone]

B

change this TO: fuel tank>>Racor>>pump

Behold, for I have seen the light and it is good.

.................... or about as good as you're gonna get around here.

 

[odaydokay]

I was talking about O'Day boats as sent from factory. No C-boats in that family. No Racors on O'Days of that generation unless you add one. As I said, no issues for me with tank to Facet pump (with screen) to engine spin on filter. I did have a Racor added later, just before engine filter. Never an issue, but maybe I am just lucky.

 

[Davidasailor26]

Never an issue, but maybe I am just lucky.

Yep, I think that’s what it comes down to. Our 28 had the Facet screen clog during a thunderstorm from waves and powerboat wakes stirring up the tank. The telltale sign is that the pump will only click once very few seconds when clogged. With the modification to move a filter before the pump you don’t need to rely on luck.

 

[odaydokay]

I see your point but if you have so much junk in the tank won't it clog up the filter before the pump all the same result in the end?

 

[Davidasailor26]

I see your point but if you have so much junk in the tank won't it clog up the filter before the pump all the same result in the end?

Eventually, yes, but the advantage of a “real” filter is that it’s designed with a lot more surface area of the filter media. The extra surface area means it can hold a lot more junk before being clogged. That gives a lot more opportunity to recognize a problem during a routine filter change rather than having a sudden stop.