Surging Universal diesel

[pullark]

Hi All,
I've just purchased a Catalina 30 with a M25XP diesel. The motor has an uneven idle and the revs tend to surge( go up and then go down in a continuous cycle). It has the same issue at low revs but is less noticeable at higher revs say up to 2200. The motor has 1000 hours on it and has been well looked after. It has never stalled and doesn't seem to have any problem running at cruising speed. I'm wondering what might be happening here. I'm thinking there is no issue with fuel supply but maybe there's a dirty or partially blocked injector? Anyone experienced these symptoms?
Speaking of injectors I see new ones can be bought for around $70 each. Is this a cheaper or similar cost to getting the old ones serviced or rebuilt (assuming I removed them myself)?
Appreciate your thoughts..
Kevin

 

[Anonymous 121765]

Pull,

Diesels are pretty simple. all they require is clean fuel & oil. You should troubleshoot first from the fuel tank back on to the engine. I don't know the year of your boat, but fuel tanks need cleaning from time to time.

Hope you have a primary & secondary filter setup and always carry extra filters. By your surging problems, I would suspect the fuel system first.

The pickup tube has a screen bottom, that always clogged up for me. I removed it and only use diesel fuel that is as clear as water. I cut a 6x6 access in my tank and cleaned it. There was alot of grey sludge. I never fuel up at dockside, but carry my fuel to the boat.

You can get your fuel "polished", but I don't know how really well it cleans your tank bottom. My sludge was pretty thick. Or find a local authorized marine engine rep. and talk to them and come up with a plan.

CR

 

[Stu Jackson]

Kevin, CR pretty much described what i would do. Sounds like fuel system issues. You may be interested in the trove of M25 engine information on our C34 website Tech wiki: http://www.c34.org/wiki/index.php?title=Diesel_Engine

If you back up to the main wiki page, there's another whole page on fuel.

Same engine, different boats, many other systems are exactly the same.

 

[DanM]

Kevin,

This would be a longshot but it's easy to check.

I had a surging problem on my M18 of about 75 - 100 RPM and while I was looking at every part of the fuel system for an air leak or something like that I happened to notice that the alternator field wire was mostly broken and was making intermittant contact. The surging I was getting was actually the alternator load coming on and off the engine when the field wire would make or break.

Weird and random, and probably old boat related, but easy to check just in case.

Good luck, and let us know what you find.

 

[pullark]

Feedback

Thank you guys for your thoughts,
Dan I think you might be onto it. The motor has a high output alternator and I've noticed all the instruments also flicker as the motor surges. It seems like an on load/off load type cycle. Could well be a bad connection somewhere. I won't be near the boat for a couple of weeks but when I get to it I'll go thru all the wiring connections. I'll let you know how I get on. Thanks for the input.

Regards
Kevin

Kevin,

This would be a longshot but it's easy to check.

I had a surging problem on my M18 of about 75 - 100 RPM and while I was looking at every part of the fuel system for an air leak or something like that I happened to notice that the alternator field wire was mostly broken and was making intermittant contact. The surging I was getting was actually the alternator load coming on and off the engine when the field wire would make or break.

Weird and random, and probably old boat related, but easy to check just in case.

Good luck, and let us know what you find.