Westerbeke Hunts-Misses at idle

[rlopatterson]

I have a Westerbeke 46 that is based upon a Mitsubishi block that hunts really bad between 600 and 1000 rpm in a Pearson 365. It also sounds like it diesels more than it should over idle.

- The engine does not smoke at all, and appears to run smartly above 11K rpm.

- The engine starts right away with no more than 10 seconds on the glow.

- The hunt or miss is constant with temperature and actually gets a little worse at op temp.

- There seems to be some flutter in the gauges, I suspect corrosion in the wiring or bad alternator. But most likely unrelated.

- Valves were adjusted

- Cold compression test showed #2 about 65# less and just under spec.

- Test bleed off each injector showed no noticeable fuel delivery issue. They all sounded the same.

- There does not seem to be any excessive blow by.

- The engine is a 1985 model and has 624 hours. The prior owner repowered with it in 1992 when it had about 250 total hours on it and stated it has always run that way. I have never seen one hunt and miss like this and actually noisier than a 4-108.

- No loss of antifreeze or oil mix.

- Replaced the motor mounts.


I am told that the most likely suspect would be a leaky valve or head gasket. Would a leaky valve not create more smoke? And where the head gasket was leaking would be a mystery since none in antifreeze, etc.

If the head gasket was leaking between cylinders, would that also be more indicative by noise/smoke and compression difference in the two?

I saw another post with someone else having issues like this, but never found what the resolution was.

HELP! It is driving me crazy.

[Stu Jackson]

Inital impressions:

fuel issues

too low idle speed

[rlopatterson]

Fuel is good.

Did think maybe pump is not creating good pressure at low RPM or the injectors not firing. Injectors were recently done. Don't want to go pump route until exhausted all other easy.

Checked idle with strobe. Throttle back setting is @ 850 and spec. I push it forward to 1000 to smooth it out.

I am not trusting of this engine for offshore running like this.

I thank you for ideas. keep coming

[sailorchic34]

As you already tested each cylinder with no change between cylinders we can generally rule out compression / head gasket fault.

As Stu said low idle. Try setting the idle to 800-900 and see how it runs.

Could also be loose governor spring/linkage which could cause hunting.

[rlopatterson]

Originally Posted by sailorchic34

As you already tested each cylinder with no change between cylinders we can generally rule out compression / head gasket fault.

As Stu said low idle. Try setting the idle to 800-900 and see how it runs.

Could also be loose governor spring/linkage which could cause hunting.

There was a 60# difference in #2 that was just under spec. We didn't think it was enough to cause too much panic or the cause?

Idle is currently set @ 850. 1000 is where it evens out. Set by light and not the tach. Both agree.

Can't find anything on governor spring/linkage. Have to believe that is internal to the Injection Pump as there is nothing outside except throttle linkage and shutoff valve. Only adjustments on pump are on linkage for idle and top speed adjustments.

[a64pilot]

Try running either Techron or Sea Foam in the fuel and see if it clears up in a few hours, the excessive "Diesel sound" at idle is indicative of dirty fuel injectors as well as an unstable idle. Basically varnish builds up on the injector tips and instead of a nice spray, you get streams , used to use automatic transmission fluid as a fuel additive to clean injectors back thirty or so years ago as it's a high detergent 10W oil I believe.
You could of course remove you injectors and have them tested / cleaned as well.

When you fix it, let us know what was wrong.

[rlopatterson]

Originally Posted by a64pilot

Try running either Techron or Sea Foam in the fuel and see if it clears up in a few hours, the excessive "Diesel sound" at idle is indicative of dirty fuel injectors as well as an unstable idle. Basically varnish builds up on the injector tips and instead of a nice spray, you get streams , used to use automatic transmission fluid as a fuel additive to clean injectors back thirty or so years ago as it's a high detergent 10W oil I believe.
You could of course remove you injectors and have them tested / cleaned as well.

When you fix it, let us know what was wrong.

Replaced engine mounted fuel filter and filled with Seafoam before installing. Ran it through and not different before/after.

Leaky injectors would usually get white smoke?

Yes, I am about to start pulling it all a part now. Parts are so expensive for this thing, I hate to tear anything down unless I really have to.

[a64pilot]

Real bad injectors would smoke, I think mostly grey, white would be pure un-burned fuel, I've never had an injector that bad, but maybe if one lost a tip?
I've never ran straight Sea Foam through a Diesel before, unsure how much that would clean or maybe just pass through too fast?
I've had in my past a couple of Mercedes Diesels that would pick up a knock at idle that running transmission fluid in the fuel was the fix for, now that was in the 70's, and I had an old John Deere 310 Backhoe that would only idle on two cylinders it's injectors were so varnished up. I was going to remove the injectors, but was talked into trying the Techron and it worked. None of these smoked, just sounded like crap at idle and idled rough, especially the JD, a three cylinder Diesel running on two is not very smooth.

[Saltyhog]

Originally Posted by rlopatterson

Replaced engine mounted fuel filter and filled with Seafoam before installing. Ran it through and not different before/after.

Leaky injectors would usually get white smoke?

Yes, I am about to start pulling it all a part now. Parts are so expensive for this thing, I hate to tear anything down unless I really have to.

Westerbeke parts are insanely expensive. See if you can find an industrial Diesel repair place. It's a Mitsubishi 4DQ5. Parts direct from Mitsu are far more reasonable. Don't mention it's a Westerbeke. The HP pump is the first place I'd look. Check closely for leaks and or weeping. Apparently these pumps, although very good pumps, are prone to problems with the new(ish) low sulfur fuel.

[a64pilot]

You can pull the pump and have it bench tested for not much money. My current Backhoe (a JD 410A) that I rebuilt twenty or so years ago when I had the pump re-built I was told the pump was so worn that pressures at starting RPM would be so low that it would be difficult to start. It's been starting fine for twenty years, but apparently a worn pump first shows up as hard to start due to low pressures, not a bad idle?

On edit, if your pulling the pump to have it tested, take the injectors too and have them "pop" tested at least, a leaker will do what your saying your does too, I think.

[rlopatterson]

Originally Posted by Saltyhog

Westerbeke parts are insanely expensive. See if you can find an industrial Diesel repair place. It's a Mitsubishi 4DQ5. Parts direct from Mitsu are far more reasonable. Don't mention it's a Westerbeke. The HP pump is the first place I'd look. Check closely for leaks and or weeping. Apparently these pumps, although very good pumps, are prone to problems with the new(ish) low sulfur fuel.

I called a couple of Mitsu parts dealers. The few that carried or could get parts for the 4DQ5 asked directly if it was a Westerbeke. I would have to lie to them in order to get real parts. One dealt with China parts that he claimed were the same as oem.... no thank.... but only had gaskets and lower end parts.

They said that if Westerbeke found them selling parts for a Westerbeke, they would get sued and Westerbeke is serious about it.

[tdoster]

WOW. I had a similar issue on my W46. My issue was a bad valve, but was down 100 psi on #3. Same issue, ran great at higher rpm, but idled like snot. Top end overhaul cost about $2K total.

We still plan to repower this fall or next spring because we plan to cruise for a couple years and would rather leave with a new motor. So, will have a W46 with 850 hours that spent half its life in fresh water to a good home at that time. Will pull the BCD5 genset out at the same time, don't need the genset - it has less than 500 hours. Both wont be ready until then since it is a pain to haul the boat where we are now.