engine over revs at idle

[RAD]

I have a Westerbeke W30 and over the summer while cruising it would race up for 10 seconds and go back to normal.....and I was afraid it would get worse :cussing: so todays problem while running it in the slip to get the oil warm for an oil change it would slowly creep up in RPM's without me being near the throttle and if I shut it down and restart it would idle fine and do the same thing
I'm thinking bad injectors or one out of the four......me thinks it might be dribbling fuel and not spraying
anyone been through this?

 

[Don12364]

If you have any engine oil 'blow by' getting past the piston rings it could well be running on this.
Under these conditions the faster it runs the more oil gets past the rings so - it runs even faster.
Ultimately there could be complete runaway until the engine self destroys.
It has happened many times.
With any luck it could just be the result of having overfilled it with oil.
Alternatively it could be fuel leaking from the lift pump diaphragm into the sump and this being vaporised and getting past the pistons.

Nothing you do with the throttle will stop the engine so you need to put your hand completely over the air intake and smother it. Not without risk to life and limb on an engine running flat out.

Don't want to worry you unnecessarily but I suggest checking the oil level as a first step and, if okay, then a compression test before running it again.

 

[RAD]

Checked the oil level and all was good and did an oil change and the right amount came out....that was the first thing I thought of ......I can stop the engine with the fuel shutoff cable which is connected to the injector pump.
I either have an issue with the injector pump or the injectors......forturnly I found out that this engine is the same as the British Leyland BMC 1.5 and found a supplier in the UK that has parts at a decent price but the injector pump might have to be rebuilt if that the problem cause that cannot be found too easy and this engine doesn't have a ton of hours on it so I'm thinking the IP might be ok

 

[Maine Sail]

RAD,

Try holding the throttle arm in the idle position manually and see if this still occurs. Sometimes the cables become stiff and can do this. If holding the throttle arm solves it replace the throttle cable or adjust the tension at the pedestal or place a U-Bolt around the cable and gently tighten it to get some resistance.

Check the easy things first. Ruling out throttle creep is easy just hold it in idle with your thumb....

 

[RAD]

I tried keeping the throttle back at the idle position at the engine and had no change, I'm starting to think that the over rev problem and this is all related to last summers problem the boats ready to get hauled for the winter so I'm hoping to get some direction soon......I cannot spend too much time down at the boat cause I'm an electrician and the most popular guy these days restoring hurricane damaged homes

 

[Chris Patterson]

It sounds to me like it's trying to run OUT of fuel. A diesel will do that with a too lean mixture, ie: more air, less fuel. The injectors letting fuel "drip" into the chambers more often than not will shut down the engine. If the fuel is too much to the excess, the combustion process is inefficient, as it generally needs the sprayed/atomized structure to detonate properly.

Just a wild shot without looking at it of course..

 

[Dan Hill]

Diesels don't have lean or rich mixtures. More fuel....more rpms, less fuel.....less rpms. This is why diesels don't have a throttle plate and don't create vacuum, they don't need them. Your issue is with fuel delivery control. Start simple with external controls and work inward. Personally I would investigate your governor system, if it has one. Good luck with your search!

 

[petersea]

OK one more thing to check ............make sure your fuel return line is clear.....years ago in a effort to get faster (more rpm) trucks we used to intentionally restrict the return fuel line and increase fuel pressure thus put more fuel in cylinders. High idle was a common problem with doing this, shutting engine down would reduce pressure until it built up again....may not be your problem but can't hurt to check it. I don't think a injector that is bad would make your engine act like this, more likely pump issue

p.s. I would not advise anyone to intentionally restrict the return line

 

[RAD]

UPDATE
I had posted this on another forum and a real nice fellow from the left coast gave me some insight on the problem.....Peter is right on the nose where I should be looking, all this started back in the summer when I decided to change the CAV fuel filter to a spin on type adapter and the engine ran fine till half way through my trip so I put it all back the way I found it (thankful I saved all the old parts and had a new filter) and old Westy was happy again till later in the season when it acted up again, now the only items that got touched was the normal gaskets and O rings associated with a filter change but I had to loosen a return banjo fitting that returns from the injectors and the the fuel tank (both under the same banjo)to remove the center bolt when I did the adapter change. so I'm going to start all over with fresh gaskets,filter,copper banjo washers,check return line and hope for the best

 

[RAD]

********UPDATE***********
found the problem and solution
this spring when I launched I had the engine racing to a higher RPM as soon as I started the engine and the problem seemed to have gotten worse so after looking around EBay and finding a used and obsolete ejector pump and looking at what kind of a project it is to change I realized that although the manual says to only bleed up to the filter head when changing filters that maybe there's air in the injector pump so lets do a complete bleed and then after finding air at the filter head I thought about my fuel lines from the tank to the first filter and the emergency electric pump were braided stainless steel lines leftover from my Chris Craft renovation back in the eighty's......those lines were hanging around in a box in the shop attic for decades and although they worked for a few years I figured that the rubber under the braid could be rotting and decided to buy new Coast Guard approved fuel lines and fittings and change it all out and now my old Westerbeke has been running great