Possible Air leak in M25 fuel line?

[Tim S.]

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, 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 a leak at the base of the injector, can I just tighten it somehow, without removing it, replacing washer, etc?

 

[Stu Jackson]

The very LAST thing you need to do with an M25 is to touch the injectors. You have the bleed screw or knurled knob for bleeding.

Read these:

Bleeding 101 Bleeding M25 Series Engines 101- A Summary of Links for You

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

********************

Engines 101 - The BIGGEST & BEST collection of M25 Series Universal Engine Information on the Internet, plus some M35, too This includes a link to the Critical Upgrades topic which has more engine information please read it too.

Diesel Engine - c34.org

 

[jviss]

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, 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 a leak at the base of the injector, can I just tighten it somehow, without removing it, replacing washer, etc?

Welcome to the forum! I hope you sort this out. The M25 is a wonderful engine. If it's an old installation, just replace ALL of the fuel lines.

(BTW, it's poor form here to post the same question in multiple forums.)

 

[capta]

Is your fuel/water separator empty when you go to check it? This would indicate the leak is tank side of the filter. If you are at your wit's end, you could try pressurizing the fuel line and see if the leak will show itself. If you don't want to do that, or it proves unhelpful, then all you can do is check every hose clamp and inch of hose very, very carefully, as an air leak will often not show itself as a fuel leak.
All that being said, most diesel fuel line air leaks are caused when the filter is reassembled after changing the element.

 

[LeslieTroyer]

Two things.
1). If you are getting bubbles from injector to block(and not fuel/bubbles dripping from hp lines) replace your copper washers under the injectors. I’d you’ve been bleeding from injectors (not a good idea as Stu says) replace copper there.
2) if you replace your soft fuel lines be sure to use Coast guard approved fuel lines… not automotive.
3) the 45 minute run time may be indicative of a clogged vent line - insects loveto build homes there.

 

[RitSim]

I have found it helpful to add a short piece of clear PVC tubing right before the feed to the injector pump. If you have a leak, you will see air bubbles in the clear line. Remove after testing.

 

[captcoho]

Is your fuel/water separator empty when you go to check it? This would indicate the leak is tank side of the filter. If you are at your wit's end, you could try pressurizing the fuel line and see if the leak will show itself. If you don't want to do that, or it proves unhelpful, then all you can do is check every hose clamp and inch of hose very, very carefully, as an air leak will often not show itself as a fuel leak.
All that being said, most diesel fuel line air leaks are caused when the filter is reassembled after changing the element.

Might also try just turning the key on and the fuel pump should slow or stop ticking completely.
You can then touch around the fuel line and wiggle it a bit and listen to the pump if it starts ticking faster.
A leak in the return line is not under as much pressure and will not cause the engine to stall.

 

[captcoho]

Is your fuel/water separator empty when you go to check it? This would indicate the leak is tank side of the filter. If you are at your wit's end, you could try pressurizing the fuel line and see if the leak will show itself. If you don't want to do that, or it proves unhelpful, then all you can do is check every hose clamp and inch of hose very, very carefully, as an air leak will often not show itself as a fuel leak.
All that being said, most diesel fuel line air leaks are caused when the filter is reassembled after changing the element.

This could be a possibility, I've seen the filter/separator not seal the best and allow it to create a small leak.
The old units had a plastic bowl that shouldn't have to be cranked for the o ring to seal. But being old, hot, and overtightened over the years can cause a small insidious leak and the old plastic racor filter bodies should be replaced.

 

[Davidasailor26]

3) the 45 minute run time may be indicative of a clogged vent line - insects loveto build homes there.

That was my first thought based on the regular timing too. Not really consistent with the bubbles, but I think it’s worth running the engine with the fill cap open, or at least cracking it open periodically as a test.

 

[jssailem]

worth running the engine with the fill cap open, or at least cracking it open periodically as a test.

A temporary test. Not a regular arrangement. Would permit water to enter the tank. Not a good practice.

 

[jviss]

A temporary test. Not a regular arrangement. Would permit water to enter the tank. Not a good practice.

Ya think?

 

[Tim S.]

UPDATE: After following much of the above advice, replacing all filters, professionally purging and "polishing" the fuel, draining separator and replacing element, etc. The engine continued to stall. But randomly or seemingly in waves/rocking boat situations. On flat water, it ran well for 14+ hours. (this is why I had to take the ICW vs ocean-route on my journey). The Final hypothesis is this...the LIFT PUMP works, but only intermittently. So that while it clicks when key is turned, it does not reliably provide a constant low PSI to the Injector Pump. HOWEVER, in calm conditions, the engine's injector pump is sufficiently strong to PULL the fuel forward - and keep the engine running (as long as the system is stable, flat, etc). I read online someone saying his engine did this. I believe this is most likely the problem, because after a stall I'd open the bleed screw and wait for fuel spurts. Sometimes the fuel would appear quickly. Sometimes it would take over a minute to arrive at the bleeder screw. Close the bleed screw, start the engine, and it would run for many, many hours. EVERY TIME, same thing. Long run. Stall. Bleed. Engine starts and runs well. Thank you all for your help. I have a purchased a new lift pump - which I will install prior to next voyage. If you don't see another update here, that was indeed the source of the problem. A very difficult diagnosis, because the lift pump clicks 100% of the time - and clearly does work, but only intermittently. The "occasional delay" in its ability to get fuel to the bleed screw is the indicator/symptom that I missed when trying to figure this out.

 

[Sinnerman]

If it stalls, try removing the deck fill cap to vent the tank and see if it comes back to life. If it does, it is the clogged vent line as one person already stated.

If not, clogged fuel line. Pull the fuel pickup tube out of the fuel tank and check for black slime/snot/snails ...blocking it.

If you have the cylindrical electrical fuel pump, there is a removable filter screen built into the bottom of it which may be clogged up as well.

The Unknown Filter

Catalina Direct, publishers of the Catalina 22 and Catalina 25 Owner's Handbooks and the largest supplier of parts and Lewmar winches for Catalina Yachts in the country

www.catalinadirect.com

cheers