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BMC 1.5 Fuel Delivery System


Freedom21Foot

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Hi Folks.

First post in here. Actually first boat I've owned, and first engine I've attempted to fix. So appreciate all the help I can get.


I have 3 out of 4 working injectors. I also have fuel being delivered to all 4 fuel lines by the fuel pump. But for some reason, I have no fuel coming through the injectors.

I've put a video here to demonstrate: https://youtu.be/8Df_UCQf6T8

I can think of a few reasons why this might be, including no lack of pressure from the fuel pump. But before I go taking the fuel pump apart or replacing it, are there other reasons this might happen?

Many thanks in advance.

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Interesting but as the open injector pipe should have bled the pump the only other thing I can think of is air trapped in the injector pipes. What was the break pressure when you were testing the injectors on a rig? In case the injectors have been set too high.

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4 hours ago, Boater Sam said:

If you have not bled the nipple on the injector pump body, you will never get any injection pressure.

1.5D engine injector pump will NOT self bleed from the injector pipes.

Thanks for your input Sam. I followed this video for bleeding. Which one of the nipples are you referring to? The one on the top or the side?

 

Edited by Freedom21Foot
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The one on the round barrel side, but you can do both anyway. The one near the injector pipe union is  supposed to avoid having to slacken any injector pipes but it only bleeds one injector, better to bleed the lot. Open and prime with the lift pump hand lever or crank if you don't have one.

The nut  with a lock nut on the pumps NOT a bleed nipple! It controls the stall rate.

 

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19 hours ago, Freedom21Foot said:

Hi Folks.

First post in here. Actually first boat I've owned, and first engine I've attempted to fix. So appreciate all the help I can get.


I have 3 out of 4 working injectors. I also have fuel being delivered to all 4 fuel lines by the fuel pump. But for some reason, I have no fuel coming through the injectors.

I've put a video here to demonstrate: https://youtu.be/8Df_UCQf6T8

I can think of a few reasons why this might be, including no lack of pressure from the fuel pump. But before I go taking the fuel pump apart or replacing it, are there other reasons this might happen?

Many thanks in advance.

What's wrong with the 4th injector?

 

My experience is if I crack open a high pressure pipe to just one injector, whilst running, the engine will die.

 

So perhaps I'm not that surprise that with one open pipe there is sufficient leakage in the pump such that it won't build up to the 'opening' pressure for the other injectors.

 

As another poster has asked, what were the opeing pressures on your test rig?

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1 hour ago, Mikexx said:

What's wrong with the 4th injector?

 

My experience is if I crack open a high pressure pipe to just one injector, whilst running, the engine will die.

 

So perhaps I'm not that surprise that with one open pipe there is sufficient leakage in the pump such that it won't build up to the 'opening' pressure for the other injectors.

 

As another poster has asked, what were the opeing pressures on your test rig?

 

1. The engines usually misfire on the open injector unless there is something very wrong. Its a very common way of determining which cylinder may be suffering a misfire.

 

2. Once the element on an in-line pump has risen and close the ports or the inlet port in rotor shaft in the DPA pump has turned past the mating port in the body then fuel will be trapped in the pumping chamber. When the element rises or the DPA plungers come together there is no way out for the fuel apart from via the injector port so whatever any other injector or injector pipe may be doing it can have no effect on teh fuel delivered to that one injector.

 

If the pump is well worn then some fuel may be able to pass back and leak from the rotor shaft inlet port back into the body but the governor should cause more fuel to be driven into the plunger chamber to compensate. In any case at cranking the DPA should set itself to maximum fuel.

 

Sorry to say this Mike but I suspect you have a sick engine and injector pump. Just in case your problem is related to insufficient fuel pressure in the pump body (not injector pipes etc.) once you are sure your filters and lift pump stainer are clear try removing the big hexagon where the fuel inlet connects to the pump. There is a nylon strainer (plus springs and a plunger) in there that may be partially blocked. Observe extreme cleanliness and swill the parts min clean diesel as you reassemble.

 

Re your last comment. the OP has had plenty of time to tell us and as he seems to have chosen not to I suspect he may have done a DIY injector overhaul and set the pressure too high which he now realises and maybe has put it right.

Edited by Tony Brooks
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1 hour ago, Tony Brooks said:

 

Sorry to say this Mike but I suspect you have a sick engine and injector pump. Just in case your problem is related to insufficient fuel pressure in the pump body (not injector pipes etc.) once you are sure your filters and lift pump stainer are clear try removing the big hexagon where the fuel inlet connects to the pump. There is a nylon strainer (plus springs and a plunger) in there that may be partially blocked. Observe extreme cleanliness and swill the parts min clean diesel as you reassemble.

 

 

I was wondering the state of my pump. Things is it seems to work very well in every other apsect so reluctant to change it. I do have a spare for that time when all goes pear shaped.

 

Perhaps I have injectors with well-matched opening pressures!

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1 hour ago, Mikexx said:

 

I was wondering the state of my pump. Things is it seems to work very well in every other apsect so reluctant to change it. I do have a spare for that time when all goes pear shaped.

 

Perhaps I have injectors with well-matched opening pressures!

No. As I said once the fuel is in the high pressure pumping chamber it is trapped so can't affect other injection pulses. The DPA could leak fuel past worn plungers or worn rotor shaft or body but unless it was really bad the engine would slow down because of the lost fuel so the governor would allow more into the pumping chamber to make up for the leaking fuel. The DPA fitted to the 1.5 and probably the 1.8 has just one pumping chamber with two opposed plungers in it. These are operated by two sets of opposed "bumps" in the cam ring so even if one set of "bumps"/cams were worn it would only affect two cylinders. Once the fuel is trapped in the pumping chamber and fuel compression starts the pressure will rise until either any air bubbles in the fuel are compressed or the injector opens. If the air is of sufficient volume the bubble will never be compressed enough to allow the pressure to rise sufficiently to open the injector. If the plungers run out of movement before injection pressure is reached then no injection will take place. Internal fuel leakage might allow this but then you would probably lack maximum power.

 

If you can get the maximum power you need I very much doubt there is much wrong with your injector pump. However if loosening just one injector stops the engine its not normal. If it starts easily from cold then it is unlikely to be a compression problem unless the valve clearances are too tight so hold valves open when hot. It could be pump timing I suppose but its hard to get that wrong on these engines unless the pump and/or cam drive is worn.

 

If it does what you what reliably then put it down to juts one of those things and enjoy boating, certainly do not go spending time or money on trying to find out what is going on.

Edited by Tony Brooks
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On 24/06/2018 at 15:29, Tony Brooks said:

No. As I said once the fuel is in the high pressure pumping chamber it is trapped so can't affect other injection pulses. The DPA could leak fuel past worn plungers or worn rotor shaft or body but unless it was really bad the engine would slow down because of the lost fuel so the governor would allow more into the pumping chamber to make up for the leaking fuel. The DPA fitted to the 1.5 and probably the 1.8 has just one pumping chamber with two opposed plungers in it. These are operated by two sets of opposed "bumps" in the cam ring so even if one set of "bumps"/cams were worn it would only affect two cylinders. Once the fuel is trapped in the pumping chamber and fuel compression starts the pressure will rise until either any air bubbles in the fuel are compressed or the injector opens. If the air is of sufficient volume the bubble will never be compressed enough to allow the pressure to rise sufficiently to open the injector. If the plungers run out of movement before injection pressure is reached then no injection will take place. Internal fuel leakage might allow this but then you would probably lack maximum power.

 

If you can get the maximum power you need I very much doubt there is much wrong with your injector pump. However if loosening just one injector stops the engine its not normal. If it starts easily from cold then it is unlikely to be a compression problem unless the valve clearances are too tight so hold valves open when hot. It could be pump timing I suppose but its hard to get that wrong on these engines unless the pump and/or cam drive is worn.

 

If it does what you what reliably then put it down to juts one of those things and enjoy boating, certainly do not go spending time or money on trying to find out what is going on.

 

Perhaps there's an issue with the governer? I had assumed the clearance in the pump might be increased so the 'distrubutor' might leak fuel badly enough to divert fuel to the other fuel lines.

 

It starts easily with a modest time on the glow plugs. There is an occasional misfire when cold as indicated by the subsequent puff of smoke.

 

It revs and provides sufficient power for my needs. There is a tinge of blackness to th smoke at full throttle.

 

The pump was timed to minimise smoke!

 

As you intimate, I am reluctant to make any changes!

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The tinge of black smoke at full throttle is more likely to be a slightly oversized prop than a fuel system fault but a fuel fault can not be completely ruled out. If the smoke goes when you ease the throttle back a little it is likely to be an oversized prop.

 

I am not going to keep on saying this but the bit about leaking fuel to the other fuel lines is twaddle. It really can't happen. Any fuel lost would leak back into the pump body and it it raised the pressure then back to the tank via the pipe that is closest to the engine block. for more info look here but you need the hydraulic DPA pump part. http://www.tb-training.co.uk/CIsys.htm

 

I agree about not spending any money if its working well enough for you although I don’t like the sound f the misfire. It might be an injector is sticky but check the valve clearances first because its cheap to do.

 

 

 

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