Diesel wont rev

[CapnSantiago]

1982 Islander 30 13hp 3 cylinder diesel intermittently wont rev when in gear (forward or reverse). Increase throttle and engine continues to just idle. Shift to neutral and engine will usually go ahead and rev although with significant delay from throttle input. Shift back into gear and sometimes will go ahaed and rev but delayed from input. Seems if revs are kept up a bit from idle it revs more normal to throttle input. Sometimes do that in neutral and then shift with engine slightly revd but concerned with clutch/transmission damage from that too much.

Of course this usually happens at the most inopertune time such as leaving the dock/slip or returning. Other times revs normal.

Any experienced input will be appreciated.

[Faster]

Fuel filters checked/cleaned/changed???

[CapnSantiago]

All seems ok there but will double check. BTW its a Volvo Penta MD7B.

[SloopJonB]

Are your throttle & shift cables (cable?) properly adjusted?

[PaulfromNWOnt]

Sounds like a cable/linkage issue. Under no load when in neutral, the engine will rev higher at the same throttle input then it will under load.

With the engine off, have someone operate the throttle while you watch the movement of the linkage.

HTH

[CapnSantiago]

Thanks for the input. Checked out the cables and linkage as you described before I last left the boat. Everything seemed to be operating freely and properly. If it were a gasoline engine I would say it was almost acting as if flooded and therefor not giving any (or giving delayed) rev response with throttling up.

Any more ideas will be appreciated. I'll be checking it out more this weekend as I'm at a point where I just can't trust the engine power will be there when I need it.

[fryewe]

Santiago, your engine response sounds a lot like mine last month when I was motoring to the yard for haulout. Everything appeared normal with linkages and fuel system. I pulled the inspection cover on the governor and found that the rack on the fuel injection pump was sticking. That rack is supposed to move very smoothly in both directions, advancing with the pull of the throttle cable and returning with spring pressure when the cable is pushed toward idle. I had some minor corrosion in the groove the rack slides in. I pulled the pump and tried to correct it. Didn't work. Put in anew FI pump (618 bucks for two cylinder Yanmar).

[TropicCat]

You didn't mention how long you've had the boat or what kind of maintenance the engine has had, or when it was done.

First the throttle delay is normal for any diesel. It's written in my Yanmar manuals, and I would assume your diesel would be similar. Marine Diesels don't have a conventional throttle like a gas engine, they mechanically move the governor (rev limiter) instead.

As for the symptoms, I suggest checking the old standbys before spending money:

1.) clogged fuel tank pickup (disconnect the fuel line and blow into the tank)
2.) barnacles on propeller and shaft
3.) air in the fuel system (bleed the system)
4.) clogged fuel filters
5.) old diesel fuel (new low sulfur fuel needs a stabilizer additive) (toss in a few gallons of new fuel)
6.) exhaust elbow clogged
7.) adjust valves (usually a 30 minute job)
8.) air in fuel return line

My apologies if you've already done this check list. My money would be on a clogged fuel tank pickup. Common with old fuel tanks

[CapnSantiago]

That's a good list thanks...I'll run thru it and hopefully avoid the $$$ fuel injection pump.

Don't know much about diesels but I am familiar with the throttle response lag you mention. This is more than that and/or has developed to more than that. Sometimes I can throttle to max and the engine just continues to idle until I do the neutral shift thing and play with it a bit. Engines been getting a bit harder to start as well taking several turns at cranking and priming.

This is my fourth summer with the boat and have checked/cleaned/replaced filters annually (and changed oil). Lake Texoma so I don't think barnacles. Fuel has been a concern of mine since I've filled the tank once during my ownership (still has 3/4 tank) but add stabilizer when I winterize. Exhaust system is new (over the winter) so don't think it could be that. I'll have to read up on the valve adjustment process.

Thanks again and I'll post how it all turns out.