Inconsistent revs (BMC 1800)

[Mark R]

Hi all,

 

After changing the injectors on my BMC 1800 everything was going well.

 

After about 4 hours of use it’s now developed a new issue. The engine doesn’t seem to maintain consistent revs. I’ve ruled out the Morse control and cables. I’ve adjusted the idle and throttle adjustment screws without any improvement (unsurprisingly). The engine is slightly Smokey but I put that down to the high revs.

 

I’m thinking that the injection pump might be at fault. 

 

As always, any opinions would be appreciated!

 

Mark

[StephenA]

So the revs hunt up and down when its running - is it a slow or quick hunting? Does it make any difference if you're in or out of gear?

[Mark R]

Hi Stephen,

 

It does it in neutral, in terms of hunting it is indiscriminate. It can be 3-4 seconds or 7-8 seconds.

Edited September 2, 2023 by Mark R

[Tony Brooks]

The fact it does it in neutral, where the fuel flow at any revs will be the lowest, concerns me. Usually, when the BMCs with hydraulic governors start playing like this, it is related to a restricted fuel flow. As the fuel delivery drops, the pressure inside the pumps also drops, which in turn allows the governor to rise to maximum fuel. Despite the lower fuel pressure, you get an increase in fuel delivery, so the engine revs up.

 

It is elimination time, so:

 

When was the fuel filter and any water trap changed/drained?

What did the contents of them look like?

When was the stainer that is usually in the top of the lift pump cleaned?

When was the bottom of the fuel tank drained for water/muck.

 

Is the hole in the banjo bolt that holds the injector leak off pipe onto the filter head clean (0.5mm).

 

There is another strainer under the big hexagon where the fuel enters the injector pump, but I would not advise that you

 do not touch that for now.

 

It might also be a small   air leak into the system.

 

[john.k]

Hunting at one particular revs used to be common in 6/354 Perks in trucks with hydraulically governed DPA pumps .......on my little Inter ,it was undriveable at a certain throttle position.........which you soon learn to avoid .......In bigger trucks ,it didnt matter at you were either idling ,or flat to the floor...........The fault disappeared when hydraulically governed pumps were obsoleted ,and only mechanical DPA s or the Bosch VF pumps used.

Edited September 3, 2023 by john.k

[Tony Brooks]

A further thought. Is the engine oil level as it should be, or is the oil thin and badly over full?

 

And even more unlikely, has a can of something volatile fallen down and is dripping volatile  gasses into the engine room. I heard of one instance where a can of spray paint had been left on the uxter plate, and it had fallen down and wedged between swim and engine. Vibrations caused it to periodically spray into the engine bay and the butane propellant was feeding the engine.

Edited September 3, 2023 by Tony Brooks

[Slim]

Apart from swapping out the injectors exactly what else did you do? When my BMC 1.8 developed the same symptoms I spent months and months trying to track down the cause. In the end it turned out to be air getting into the fuel line between the tank and the lift pump ie on the low pressure side. Absolutely no hint of a leak. I found it by pressurising the fuel line using a tyre pump. Bubbles out of a fitting that had been checked many times and that had shown no hint of a leak.

[Tracy D'arth]

It must be fuel related.

Either its not getting a consistent delivery to the injection pump or there is air getting in somewhere on the low pressure side.. 

So check all filters are clear, not forgetting the one in the lift pump, and every union for air getting in,

[MtB]

5 hours ago, Tracy D'arth said:

It must be fuel related.

Either its not getting a consistent delivery to the injection pump or there is air getting in somewhere on the low pressure side.. 

So check all filters are clear, not forgetting the one in the lift pump, and every union for air getting in,

 

Out of interest, how does one check a union for air getting in? Is there a way to definitively prove it isn't, or does one just check the joints are nice and tight with no evidence of fuel leaking out?

 

 

Edited September 3, 2023 by MtB
Clarify.

[Tony Brooks]

13 minutes ago, MtB said:

 

Out of interest, how does one check a union for air getting in? Is there a way to definitively prove it isn't, or does one just check the joints are nice and tight with no evidence of fuel leaking out?

 

 

That is about it unless you seal the fuel filler cap and pressurise the tank via the breather and look for leaks or bubbles.

Otherwise, it is dismantle all the joints, change/anneal any copper washer, change any crushed olives and reassemble. Also check the O rings on any water trap between tank and lift pump and on the lift pump cap (AC type pumps).

 

In really difficult problems, I may insert a short length of clear plastic hose into each delivery pipe in turn and look for air bubbles.

 

In the case of these and similar engines, it is important to ensure the 0.5mm bleed back to the tank from the top of the filter is clear, because its job is to return small air bubbles in the fuel back to the tank.

Edited September 3, 2023 by Tony Brooks

[Slim]

4 hours ago, MtB said:

 

Out of interest, how does one check a union for air getting in? Is there a way to definitively prove it isn't, or does one just check the joints are nice and tight with no evidence of fuel leaking out?

 

 

Not definitive but one way is to apply positive pressure to fuel lines with some form of compressed air whilst using soap or similar on the joint. Shirley you've done that to a gas pipe any number of times.😶 

[MtB]

7 minutes ago, Slim said:

Not definitive but one way is to apply positive pressure to fuel lines with some form of compressed air whilst using soap or similar on the joint. Shirley you've done that to a gas pipe any number of times.😶 

 

Well that checks for air leaking OUT, I was asking about a method of definitively proving it isn't leaking IN. Stranger things have happened. 

 

 

[Slim]

Just now, MtB said:

 

Well that checks for air leaking OUT, I was asking about a method of definitively proving it isn't leaking IN. Stranger things have happened. 

 

 

Yes, but if gentle pressure one way on a joint shows a breach then it stands to reason pressure the other way (even mild) might find the same breach. 

[john.k]

An air leak would be quite obvious when the engine starts ,then stops after a few seconds ..........if you have an air leak,then using the primer on the lift pump will indicate air in the fuel system......as will disconnecting the bypass line back to the tank while the motor is running. It will have frothy fuel ,not a solid stream................having established that there is an air leak ,then the traditional method is to pressurize the line with low pressure air ,and spray detergent /soapy water over the line ......the  leak will make a mass of bubbles.

[Mark R]

Morning guys,

 

Thanks for all your advice. Apologies for the delay in replying. I did a few checked yesterday as Tony suggested, this included checking the lift pump filter (dirty, so cleaned). The fuel filter was changed a week ago (I did however remove and checked it and it appears fine).

 

The banjo bolt on top of the fuel filter doesn’t have a hole in it, I’ve added a picture to show the type of bolt that was attached. The boat has been running with this bolt in place so not sure that’d be the issue.

 

I couldn’t say 100% that the oil wasn’t thinner than expected but the oil level hadn’t appeared to move upwards (or downwards) so am assuming that there is nothing leaking into it. 

 

I’ve attached an image of a sample of the fuel, admittedly it’s not overly clean so I am going to drain the fuel tank, clean it out and add fresh diesel.

 

In reply to Slim, I didn’t change anything other than the fuel filter when I changed the injectors, however I had replaced the pipe leading from the lift pump to the fuel filter a month or too back. Given the pointers that Slim and Tracy have mentioned I shall get back to the boat and check for potential areas where air might be entering the low pressure side of the fuel system. I’ll be able to cap the fuel tank and attach an inflator to the fuel system to check for potential leaks.

 

Just to add to my previous comments I did notice that on two occasions the engine stopped after idling for a few minutes but I put this down to messing around with he idling screw on the injector pump.

 

Interestingly when I cleaned the fuel lift filter I thought I’d remedied the fault as the engine ran without issue for a good few minutes before it returned to the revving, I’ve a video of the engine revving but can’t add it on here.

 

Mark

 

[Tracy D'arth]

That is not a banjo bolt but the drain screw from the bottom of a fuel filter.

Which type of fuel filter head is it? Can we have a picture of it please?

That fuel is filthy and has water contamination.

 

 

 

 

 

 

 

[David Mack]

21 minutes ago, Mark R said:

I’ve a video of the engine revving but can’t add it on here.

Upload it to YouTube and post a link here.

[Alan de Enfield]

 

Is that glass that shape inside (ie is the diesel sittng on the bottom of the glass).

 

Ie a 'heavy bottomed glass'

 

 

If not then you have a serious case of water contaminated diesel - and, the diesel is filthy.

 

 

Mine when I had water problems ...................

Diesel sitting on water.

 

 

Edited September 4, 2023 by Alan de Enfield

[Tony Brooks]

22 minutes ago, Mark R said:

Morning guys,

 

Thanks for all your advice. Apologies for the delay in replying. I did a few checked yesterday as Tony suggested, this included checking the lift pump filter (dirty, so cleaned). The fuel filter was changed a week ago (I did however remove and checked it and it appears fine).

 

The banjo bolt on top of the fuel filter doesn’t have a hole in it, I’ve added a picture to show the type of bolt that was attached. The boat has been running with this bolt in place so not sure that’d be the issue.

 

I couldn’t say 100% that the oil wasn’t thinner than expected but the oil level hadn’t appeared to move upwards (or downwards) so am assuming that there is nothing leaking into it. 

 

I’ve attached an image of a sample of the fuel, admittedly it’s not overly clean so I am going to drain the fuel tank, clean it out and add fresh diesel.

 

In reply to Slim, I didn’t change anything other than the fuel filter when I changed the injectors, however I had replaced the pipe leading from the lift pump to the fuel filter a month or too back. Given the pointers that Slim and Tracy have mentioned I shall get back to the boat and check for potential areas where air might be entering the low pressure side of the fuel system. I’ll be able to cap the fuel tank and attach an inflator to the fuel system to check for potential leaks.

 

Just to add to my previous comments I did notice that on two occasions the engine stopped after idling for a few minutes but I put this down to messing around with he idling screw on the injector pump.

 

Interestingly when I cleaned the fuel lift filter I thought I’d remedied the fault as the engine ran without issue for a good few minutes before it returned to the revving, I’ve a video of the engine revving but can’t add it on here.

 

Mark

 

 

OK, so this is a non-typical BMC fuel system. By blowing up the filter head image one can see that the screw you show is conneted to a plastic paie that ihope runs back to the fuel tank:

 

 

As long as the flat on that screw ends up still inside the middle of the banjo I think it will leak air back into the tank, and I would be happy to rule that out as the cause for now.

 

If the sample you show came from the bottom of the tank you need to spend a bit of time trying to get all the water from the bottom of the tank, plus any other sludge. This tends to be confirmed as the problems because cleaning the filter sorted it for a short while.

 

Sort out the tank, if you have a water trap then clean it/replace its filter, and    change the fuel filter because I think it is soaked in water.

 

I suspect water on the filter paper is restricting the fuel flow, or droplets of water are causing the governor valve to stick.

 

Good Luck

 

 

 

 

 

 

 

[Mark R]

Thanks guys, attached is a picture of the top of the filter. That bolt has always been in there, I could remove the drain plug to see what that is like.

 

it makes me wonder, the boat was broken into a few weeks ago, during which they stole the knob of the Morse control and through my badge pole away. Might they have done something to my fuel? I have done about 10 hours of travel since then but had my injector issues since then too! 
 

 

[Tony Brooks]

1 minute ago, Mark R said:

Thanks guys, attached is a picture of the top of the filter. That bolt has always been in there, I could remove the drain plug to see what that is like.

 

it makes me wonder, the boat was broken into a few weeks ago, during which they stole the knob of the Morse control and through my badge pole away. Might they have done something to my fuel? I have done about 10 hours of travel since then but had my injector issues since then too! 
 

 

 

Did you read my reply. As long as the flat on that bolt ends up in the centre of the banjo it will still leak any air and a degree of fuel back to the tanks, so is 95% NOT the cause of the problem.

 

I listed what I think you need to do to solve this. Luckily, for now, there is no sign of bug, so get the bottom of the tank drained PDQ, before there is.

[Tracy D'arth]

That looks like a standard CAV filter head but the wrong banjo bolt for sure. The return tp the tank will be passing a lot more fuel than it should with that bolt with a flat on it. The hole in the correct banjo bolt is only 0.5mm to let air back to the tank.

[Mark R]

Cheers guys,

 

Sorry Tony I hadn’t seen your reply. There is no water trap. I shall get back to her in the next day or so and drain/clean it out. Should I replace the fuel filter again? I’ll look at the rubber pipe but I do believe it is a return to the tank.

 

Is there anywhere I can buy a banjo bolt or do I need to just buy a replacement filter head?

Edited September 4, 2023 by Mark R

[David Mack]

4 minutes ago, Mark R said:

Is there anywhere I can buy a banjo bolt or do I need to just buy a replacement head?

Google banjo bolt and you'll find loads. But you will need to know what thread and length to buy. Or take the existing bolt to a bricks and mortar seller and find one to match.

[Tony Brooks]

9 minutes ago, Mark R said:

Cheers guys,

 

Sorry Tony I hadn’t seen your reply. There is no water trap. I shall get back to her in the next day or so and drain/clean it out. Should I replace the fuel filter again? I’ll look at the rubber pipe but I do believe it is a return to the tank.

 

Is there anywhere I can buy a banjo bolt or do I need to just buy a replacement filter head?

 

 

1. Yes, replace the filter, 296 filters are not expensive. The filter card is probably soaked in water.

 

2.  The typical banjo and bolt is larger than the one you have, so if you replace it you will also have to replace the banjo itself and get the pipe fixed to it. Luckily, it seems that you have an adapter screwed into the filter head that your bolt screws into. I would want to see how large the hole is in that before saying your bolt is returning too much fuel. I am sure the lift pump will cope with supplying the extra fuel, especially at inland speed.

 

If you are intent on replacing them, I would suggest that you take the adapter (the larger hexagon your bolt screws into) and your bolt to a local diesel equipment specialist and see what they can supply. Otherwise, talk to Calcutt Boats, but the larger banjo and bolt they use is associated with the full injector leak off rail and has a thread to fix your rubber hose to.

 

Lots online, but you need to be sure of the thread and length, many seem to have holes in them that probably leak back similar amounts of fuel to what you already have.