Engine misfiring, likely suspects list

[sarabande]

I understand that fuel is pumped through to Cyl 4, and reaching the injector, but is there any way that the valve spring is failing under load when the injector is tight into the cylinder ?

And as a a general question, is it wise to have a spare injector on board to react to a failure ? Low probability, but highish consequence.

 

[sailorman]

I understand that fuel is pumped through to Cyl 4, and reaching the injector, but is there any way that the valve spring is failing under load when the injector is tight into the cylinder ?

And as a a general question, is it wise to have a spare injector on board to react to a failure ? Low probability, but highish consequence.

In 30 years of driving diesel cars, i have yet to have an injector fail or have 1 serviced.
if there is compression, air & fuel it must run ???????

 

[PaulRainbow]

In 30 years of driving diesel cars, i have yet to have an injector fail or have 1 serviced.

They do fail though and sometimes need to be serviced.

if there is compression, air & fuel it must run ???????

Pretty much. Timing plays it's part but the other cylinders are running fine, so that pretty much rules that out. I say pretty much, but freak failures could still allow it to be a problem.

We know he has compression and he has fuel at the pump, and certainly enough volume of fuel for 3 cylinders. So the question is, is the fuel getting into cylinder 4 correctly ?

A couple of quick and cheap tests with the injectors are still worth trying. It's worth screwing the pipe onto injector 4 with the injector out of the engine and checking that it's spraying fuel correctly (as suggested by third engines).

If it is, then that may rule the pump out.

If it isn't, that could point to the pump, or the injector (despite it passing a check). Swapping this with another injector would verify which (again suggested earlier). If the problem moves to the other cylinder it has to be the injector. If it stays with cylinder 4 it's most likely the pump.

 

[<152587>]

I don't follow this Third Engines.

If there is fuel present at the injector but the 4th cylinder is not firing, what is the point of running the engine and slackening the fuel delivery pipe on the 4th cylinder?

Richard

Richard, when dealing with a problem like this it pays to eliminate possibilities one step at a time. Prudence suggests the checks outlined in another post should be carried out to ensure the fuel delivery to the injector is of sufficient pessure to lift the injector. If that proves succesful then best to run motor to check the performance.

 

[<152587>]

Tim, you stated the compression has been checked, how and can you quantify the pressure recorded please?
Second question, are you using low sulpher fuel?

 

[RichardS]

Richard, when dealing with a problem like this it pays to eliminate possibilities one step at a time. Prudence suggests the checks outlined in another post should be carried out to ensure the fuel delivery to the injector is of sufficient pessure to lift the injector. If that proves succesful then best to run motor to check the performance.

Does that mean that it's possible for the high-pressure pump to deliver fuel to three injectors at the correct pressure but to be delivering fuel to the 4th injector at too low a pressure to lift the injector? I don't know how these pumps work but that sounds as if there is a separate pump chamber + seals for each cylinder.

Richard

 

[earlybird]

Does that mean that it's possible for the high-pressure pump to deliver fuel to three injectors at the correct pressure but to be delivering fuel to the 4th injector at too low a pressure to lift the injector? I don't know how these pumps work but that sounds as if there is a separate pump chamber + seals for each cylinder.

Richard

That's correct. AFAIK it's a Bosch MD pump which has a cam operated plunger for each cylinder. They're very reliable but I believe that plunger return springs can break, perhaps giving the symptoms seen here on the affected cylinder

 

[RichardS]

That's correct. AFAIK it's a Bosch MD pump which has a cam operated plunger for each cylinder. They're very reliable but I believe that plunger return springs can break, perhaps giving the symptoms seen here on the affected cylinder

Interesting. That's not what I would have imagined so I've learned something. And you're right .... that diagnosis does indeed seem to fit with Tim's observed symptoms.

Richard

 

[<152587>]

Iniseresting. That's not what I would have imagined so I've learned something. And you're right .... that diagnosis does indeed seem to fit with Tim's observed symptoms.

Richard[/QUOTE

Thats exactly how a cam driven plunger pump works, however do not confuse that with common rail or rotary distributor pumps. Incidentally the plungers do not have seals, they rely on close tolerances to inhibit leakage.

One point I would contest is that the diagnosis fits with Tims symptoms, remember he reported fuel at the injector that is why I have asked him to do some further tests to elaborate on this.

 

[PaulRainbow]

One point I would contest is that the diagnosis fits with Tims symptoms, remember he reported fuel at the injector that is why I have asked him to do some further tests to elaborate on this.

This is still possible. If the spring has collapsed it may be returning the piston enough to deliver a small amount of fuel. Enough to leak at the union when slackened, but not enough to develop full power from cylinder 4.

I've had some odd things with broken springs in VW PD pumps in the past.

 

[RichardS]

One point I would contest is that the diagnosis fits with Tims symptoms, remember he reported fuel at the injector that is why I have asked him to do some further tests to elaborate on this.

But when Tim said "fuel at the injector" I think he meant "fuel at the injector pipe union" rather than fuel at the business end of the injector.

I might be mistaken though as it was some time ago since I read the whole thead.

Richard

 

[PaulRainbow]

But when Tim said "fuel at the injector" I think he meant "fuel at the injector pipe union" rather than fuel at the business end of the injector.

I might be mistaken though as it was some time ago since I read the whole thead.

Richard

Not mistaken, covered in post #6.

 

[Heckler]

Does that mean that it's possible for the high-pressure pump to deliver fuel to three injectors at the correct pressure but to be delivering fuel to the 4th injector at too low a pressure to lift the injector? I don't know how these pumps work but that sounds as if there is a separate pump chamber + seals for each cylinder.

Richard

If as some one else has said, it is a plunger type pump, this might be it http://apps.bosch.com.au/aaextranet_techsearch/docs/servicebulletin/si441.pdf
If a plunger spring has broken, I have seen this happen, then the piston wont be returning to get the full amount of fuel in to the chamber, the rack position adjuster on each plunger, one could be loose or broken, no full rack movement means not enough volume of fuel being pumped. Again, i have seen this happen as well. So Richard, to answer your question, it is possible on cam type pumps for 1 cylinder not to work. The good news is that usually the amateur can take the side plate off and see if anything is broken before going any further. The idea of attaching the injector outside the engine is good to see if it is actually breaking and squirting a generous amount.
Stu

 

[Tim O]

Thanks for all the discussion folks......All helps with my learning process.

As it happens, the engineer removed the pump to take away for inspection and test yesterday! Had to make a quick decision, and right now I just don't have the time to do anything myself so bit the bullet and decided to let him proceed. Hopefully it might be something reasonably simple to fix......Fingers crossed

 

[Tim O]

Ok!

Its been a while....but we now have a diagnosis.

Apparently, after extensive testing, the problem is with the pump which simply will not deliver fuel properly at number 4 cylinder. They have swapped various bits (valves?) around and what works fine in other cylinder positions wont work in number 4, while the bit from number 4 will work fine in other positions.

Their suspicion is that it may be a hairline crack in the actual pump body/casing which opens up or causes a problem when under load.

The bad news is that it is deemed non-repairable so we are looking at a new pump from Beta Marine at around £715.

Unless anyone else has any bright ideas?

I guess I could hold out and look for a second hand or recon pump....but at the minute I cant basically move my boat off the mooring...which is frustrating to say the least....spring is a coming in!

 

[parbuckle]

You can get exchange units but may have to find the manufacturers original part no maybe not so easy on a marinised engine

Try Ebay under Kubota Diesel pump you should get an idea of cost . Refitting another unit may require some knowledge setting it up .

 

[sarabande]

There's a very good Kubota/Beta man in Bristol, known to Bilbo.

If you hang on for a bit, I'll try and get the contact details for you. It's the same pump as used in tractors !

 

[Tim O]

There's a very good Kubota/Beta man in Bristol, known to Bilbo.

If you hang on for a bit, I'll try and get the contact details for you. It's the same pump as used in tractors !

Thanks Tim.....my engineer seemed to think the pumps are modified for marine use, but maybe not?

 

[aramis]

incorrect advice

 

[sarabande]

Info from Our Man in Bristol.

http://www.hurleyengines.co.uk