Odd Idle Speed Issue

[jviss]

It's always something!

Westerbeke 38B-FOUR in my Tartan 3800. It's a four cylinder, 38HP diesel based on a Mitsubishi engine.

This weekend, when I tried to bring the engine back idle to cool down before shutting it off, it would only go down to 1000 RPM. Idle is usually around 700.

Next time it worked fine, went down to a shuddering 700 RPM.

Time after that, 1000.

What's going on? I've never experienced this before. It seems the speed control lever was making the full travel.

Any ideas?

Thanks,

jv

 

[Michael Davis]

I had a similar sounding problem with my Perkins 4-108. The RPM would jump several hundred revs at the oddest times. All went back to normal when I changed out the fuel filters. I’ve been more diligent with filter changes since then and have not had the problem again. Maybe??

 

[jviss]

Interesting, Michael. Worth a try. So far the only filters I can find are my Yanmar 4230B, which looks like a Racor. The element is supposedly a 30 micron one, p/n 4230-0100. The other filter is on the engine, a really small housing with a replaceable element.

I was assured when I bought the boat that the yard had fully serviced it, but who knows? That was Sept. 2017, and I haven't changed fuel filters yet. I have the small Weterbeke element on hand.

Any idea for an economical substitute for that Yanmar element?

 

[Michael Davis]

Interesting, Michael. Worth a try. So far the only filters I can find are my Yanmar 4230B, which looks like a Racor. The element is supposedly a 30 micron one, p/n 4230-0100. The other filter is on the engine, a really small housing with a replaceable element.

I was assured when I bought the boat that the yard had fully serviced it, but who knows? That was Sept. 2017, and I haven't changed fuel filters yet. I have the small Weterbeke element on hand.

Any idea for an economical substitute for that Yanmar element?

I’ve always had good luck at Napa or Lordco up here. I think any automotive or marine place could cross-reference it for you. I know the cost of factory parts can be pretty high compared to aftermarket.

 

[Mark Maulden]

Do you have an electronic tach? And is your alternator regulated externally with the tach signal going through the regulator? Mine is and sometimes my tach goes a little bit “off” and is attributable to the regulator shutting things down when the batts are fully charged. For me, I think this happens when the refer is off and there is no load being drawn except for plotter/AIS..Also, by ear, can you tell the difference?

 

[jviss]

Thanks, Mark, but I can hear it, regardless of what the tach says, sometimes it idles all the way down, and sometimes it doesn't.

 

[jviss]

Reflecting on this, it seems so weird. Can't be filters, can it? I was thinking it's something funny with the linkage. Will investigate Friday.

 

[SailormanDan]

I was thinking it's something funny with the linkage.

I don't have them same engine, but I've had issues with my linkage. I would rule out the linkage first, before I spend money and time on fuel filters. Good luck with it.

 

[dLj]

I would agree with making sure the linkage is working correctly as the first step. Are there electronics in the control system of this engine for the fuel injection? I am not familiar with that engine.

dj

 

[jviss]

I would agree with making sure the linkage is working correctly as the first step. Are there electronics in the control system of this engine for the fuel injection? I am not familiar with that engine.

dj

No, it's a conventional engine, all mechanical. It's a Mitsubishi, probably a tractor engine.

 

[Mark Maulden]

Does it do it at the dock? If so, take the linkage off the engine governor lever and change engine speeds down below..

 

[jviss]

Does it do it at the dock? If so, take the linkage off the engine governor lever and change engine speeds down below..

The thing is, that sometimes it works correctly, as it used to. If I lower the speed when it's running fast, it might stall out when it decides to run slow.

 

[Mark Maulden]

Then you know its probly not the linkage

 

[jviss]

Then you know its probly not the linkage

I guess I don't know enough yet to rule out anything!

 

[dLj]

It almost sounds like a timing issue - how is the injection timing controlled in this engine?

dj

 

[jviss]

It almost sounds like a timing issue - how is the injection timing controlled in this engine?

dj

I think it's geared off the camshaft, 'though not sure.

 

[kloudie1]

Yeah, disconnect at the engine and see if the lever at the helm works smoothly without sticking... Then check the engine lever to see if it is sticking (engine off) then make sure the outer cable cover clamps are not loose..