1.5 bmc over revving.

[Lochwarden]

My 1.5 BMC is revving too hard. I’ve checked for leaks, replaced the fuel filter nearest the engine with new o rings fitted. Checked the small filter under the large hexagon on top of the injector pump, it was totally clean. Slackened the idle screw right off. Removed and replaced the governor body, everything good in there. Engine oil level is normal. Engine doesn’t smoke, just the normal blue smoke at start up. The only way I can bring the revs down to a usable level is to have the engine stop half way out. Any ideas would be very welcome. 

[Tony Brooks]

Assuming the pump has an idle damper try unscrewing it one turn and see what happens - any chance you have been bleeding from the top of the pump?

 

What about the strainer in the lift pump?

[magnetman]

Is this the same engine from the other thread ? 

 

It seems to have the wrong fitting. 

 

[Tony Brooks]

5 minutes ago, magnetman said:

Is this the same engine from the other thread ? 

 

It seems to have the wrong fitting. 

 

 

If it is I have no idea what the OP is playing at, asking the same question again is only likely to get the backs up of those who had been trying to help.

 

Perhaps he should get the pump tested and overhauled. No mention of him looking at the actual governor valve as per the other thread..

[Lochwarden]

7 minutes ago, magnetman said:

Is this the same engine from the other thread ? 

 

It seems to have the wrong fitting. 

 

It is indeed. It is the wrong fitting, with no locknut. That’s how it was when I got the boat last year. 

[Tracy D'arth]

You have been told to get a longer screw and a locknut.   Have you?

 

Or are you just wasting our time?

[David Mack]

Fuel starvation. Stops the hydraulic governor working. Check and recheck there is nothing blocking the filters and the pipework between the fuel tank and the engine. If you have already checked the filters I would suspect there may be a big mass of debris on and in the end of the pickup pipe in the fuel tank.

Edited September 19, 2023 by David Mack

[Tony Brooks]

39 minutes ago, David Mack said:

Fuel starvation. Stops the hydraulic governor working. Check and recheck there is nothing blocking the filters and the pipework between the fuel tank and the engine. If you have already checked the filters I would suspect there may be a big mass of debris on and in the end of the pickup pipe in the fuel tank.

 

But from the other thread, the OP did not complain about a lack of high speed/power or revving itself up at high speed, only not idling slow enough. If it is a blockage, then surely the problem will be worse at high revs and better at low revs.

 

However, thinking more, I wonder if the lift pump is compromised so it does not deliver enough fuel at idle, but as the engine speed goes up can supply enough fuel.  I think Trevor at RCR told be about a 1.5 that would not idle until the lift pump was changed.  It might be a good idea to check the delivery volume per two cranking revolution (2 @ the crankshaft = 1 @ the camshaft).

Edited September 19, 2023 by Tony Brooks

[Lochwarden]

50 minutes ago, Tracy D'arth said:

You have been told to get a longer screw and a locknut.   Have you?

 

Or are you just wasting our time?

I’m certainly not trying to waste anybody’s time, apologies if it seems that way. I was just asking the question again, but listing the things I had done to try and fix the problem, after taking advice from my earlier question. I certainly don’t want to upset anybody. 

Just now, Lochwarden said:

I’m certainly not trying to waste anybody’s time, apologies if it seems that way. I was just asking the question again, but listing the things I had done to try and fix the problem, after taking advice from my earlier question. I certainly don’t want to upset anybody. 

Yes i have tried a longer screw with a locknut, no difference. 

[Tracy D'arth]

I considered the lack of lift pump pressure but then discounted it as I have had 1.5D engines running on gravity fed day tanks without a lift pump.

 

I would change the injection pump, or get it rebuilt by a reputable diesel shop.  I am sure that would solve the issue.

[Lochwarden]

52 minutes ago, David Mack said:

Fuel starvation. Stops the hydraulic governor working. Check and recheck there is nothing blocking the filters and the pipework between the fuel tank and the engine. If you have already checked the filters I would suspect there may be a big mass of debris on and in the end of the pickup pipe in the fuel tank.

That would make sense, thank you. I only recently added more diesel as I’ve only had the boat a year and it’s been on a marina for most of that, so perhaps adding new fuel could of stirred up muck and transferred it to the pick up pipe?   

1 minute ago, Tracy D'arth said:

I considered the lack of lift pump pressure but then discounted it as I have had 1.5D engines running on gravity fed day tanks without a lift pump.

 

I would change the injection pump, or get it rebuilt by a reputable diesel shop.  I am sure that would solve the issue.

Thank you, I will look at doing that if all else fails. 

[Tracy D'arth]

Thinking, have the return fuel pipe from the injection pump, the spill rail return and the fuel filter banjo return to the tank all been eliminated for blockage?

I had an engine where someone had used a metal braided gas hose to return fuel to the tank. It perished internally and closed completely. That engine exhibited some odd running problems until the hose was replaced.

Edited September 19, 2023 by Tracy D'arth

[Lochwarden]

2 minutes ago, Tracy D'arth said:

Thinking, have the return fuel pipe from the injection pump, the spill rail return and the fuel filter banjo return to the tank all been eliminated for blockage?

No they haven’t. I think the way forward is to start at the tank, work my way to the injectors then back again, making sure everything is leak free and unblocked. 

[David Mack]

39 minutes ago, Tony Brooks said:

But from the other thread, the OP did not complain about a lack of high speed/power or revving itself up at high speed, only not idling slow enough. If it is a blockage, then surely the problem will be worse at high revs and better at low revs.

In my case, about 40 years ago, the boat had just been craned over the then long term closed Blisworth Tunnel. On being craned back in at Gayton the crane driver swung the boat rather violently, and I later reckoned that stirred up the muck in the fuel tank. On setting off again, initially all was well, then I started to get short random bursts of high revs. These got more and more frequent until eventually the engine revs were up and down all over the place, regardless of the speed lever position. If I took the engine out of gear it screamed, and I daren't put it back into gear like that. I worked up Buckby and down Braunston racing between the locks and turning the engine off actually in the locks. I had to start it in gear again each time. Left the boat at Napton and returned a week later with my father, a decent toolkit and another BMC injector pump borrowed from someone who happened to have a spare engine. My Dad suspected a governor problem, and without much prior knowledge looked over the engine then dismantled enough of the injector pump to see how it worked and how the engine was governed. The inlet filter was full of muck. That was carefully cleaned, rinsed in petrol, dried and reassembled. Looking back along the fuel line the only other filter was a basic small inline one - the sort you might find on a small outboard or lawn mower. That was also full of crap, so much so that the moulded plastic filter in the middle had split, allowing muck through to the engine. We cleaned that, and reassembled it with a bit of the lining material from one of my mother's old skirts (just brought along in a bag of rags) clamped between the two halves of the casing. There was quite a lot of muck in the fuel tank which we couldn't do much about, but the tank contents had settled during the week, so we chanced it. On restarting the engine ran like a dream, and continued to do so until the engine was removed some time later.

In the fuel pump assembly there is a rotary pump which pressurises a chamber full of fuel, with a small hole which allows excess fuel to leave the chamber and return to the tank via the leak off pipe. On the side of the chamber is a diaphragm, which controls the stroke of the injector pump part which pumps fuel to the injectors. The speed lever also acts on this diaphragm via a spring. The faster the engine rotates the more fuel is pumped into the chamber, so the pressure in the chamber necessary to force the excess fuel out increases. The diaphragm responds to both the chamber pressure and the speed control and adjusts the amount of fuel injected accordingly. If the engine is going too fast the amount of fuel injected is reduced and vice versa. But if you starve the engine of fuel, the pump on the inlet can't pressurise the chamber, and the governor interprets this as the engine going too slowly, so increases the amount of fuel injected. That causes the revs to rise. That rise in revs in turn increases the pump speed and the amount of suction applied to the fuel inlet pipe. And as long as the pipe isn't completely blocked, that sucks a bit more fuel through, the pressure in the chamber rises, and so the fuel injected reduces and the engine slows down. All of this is then more controlled by how the debris blocking the filters or whatever behaves, and much less on what the speed lever is set at. Hence the randomly varying and generally high revs. 

Of course if the blockage is 100% complete, no fuel can get through and the engine stops. But any blockage much less than 100% can give rise to the behaviour described.

[Tony Brooks]

No diaphragms in those DPA pumps, just a piston and dashpot. I don't dispute your findings, but this problem has not been described as random, it seems to be consistent high revs at idle.  That is the differences, not random, not at high revs but consistent at idle.

[Lochwarden]

23 hours ago, Tony Brooks said:

Assuming the pump has an idle damper try unscrewing it one turn and see what happens - any chance you have been bleeding from the top of the pump?

 

What about the strainer in the lift pump?

The lift pump is only a few months old, with very very few hours use, so am assuming it’s ok.

[Tony Brooks]

2 minutes ago, Lochwarden said:

The lift pump is only a few months old, with very very few hours use, so am assuming it’s ok.

 

Did you compare the operating lever and when you fitted it did you feel the diaphragm spring trying to push the body about before you tightened it up.

[Lochwarden]

4 hours ago, Tony Brooks said:

 

Did you compare the operating lever and when you fitted it did you feel the diaphragm spring trying to push the body about before you tightened it up.

The operating lever was identical to the old one, and it fitted perfectly. I did partially refit the old one to make sure the new one felt and fitted the same. The old one was replaced as it was leaking fuel. 

[Tony Brooks]

7 hours ago, Lochwarden said:

The operating lever was identical to the old one, and it fitted perfectly. I did partially refit the old one to make sure the new one felt and fitted the same. The old one was replaced as it was leaking fuel. 

 

So unless there was a manufacturing fault that rules the lift pump out. I think it would be worth taking the "turret" with the throttle and stop levers off, so you can have a look at the actual governor valve. Just observe extreme cleanliness, and don't pull the stop or throttle spindle out of the housing, but by all means twiddle them so you can see how they move the governor.

[Lochwarden]

2 hours ago, Tony Brooks said:

 

So unless there was a manufacturing fault that rules the lift pump out. I think it would be worth taking the "turret" with the throttle and stop levers off, so you can have a look at the actual governor valve. Just observe extreme cleanliness, and don't pull the stop or throttle spindle out of the housing, but by all means twiddle them so you can see how they move the governor.

That sounds like a good idea, I will have a look today. Thank you.