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BMC 1.5 fuel system plumbing


Grockle

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Firstly may I say hello and thank you all for the useful nuggets of info I've picked up on this forum.


Can I ask you fellow BMC owners out there If I'm on the right track regarding the fuel plumbing on my (plastic) boat:


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It seems to me that the DPA injection pump is receiving unfiltered fuel that has just passed straight through the filter head without actually going through the filter itself, the return from the pump then being fed back through the CAV filter the wrong way.


I have owned this boat for the last three years and only spotted this error as I was preparing the boat for this winter. Apart from occasional tantrums I've put down to air building up in the fuel system, the engine has been a good starter and has run fine with the demands we've placed on it so far. That's probably down to information freely provided by Tony Brooks on his website - I chose to follow his recommendation of installing a sedimentor and primary filter (agglomerator) before moving the boat from where we bought it. When we got the boat the injection pump did look suspiciously new and having had no other filtration on the fuel supply before my additions, I can now see why.


I'm also puzzled by the fitting on the filter head that is currently on the return port (but is connected to the pump inlet). It can't be a non-return valve because if it was, surely the engine wouldn't be able to run?


Having read previous topics on this forum and various manuals downloaded from the web, I think I have a better understanding of how things should be on my boat. I am now in possession of the appropriate CAV non return valve, a spill rail that connects to the banjo bolt on the filter head and the appropriate banjo bolt (with the 0.5mm orifice). The new spill rail also has a fitting on the end to connect up to the tank return pipe (hopefully sending any air that's found its way into the system back to the tank). Now all I need is time on the boat to re-plumb it all.


Anything I've missed?


PS: I can't make my mind up between getting a Pela type pump for engine oil changing via the dipstick hole or whether to fit a pump to the sump plug hole. Any idea what size thread the sump plug is?

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I'm pretty sure that the filter setup is all ok - the two ports furthest from the mounting bracket marked as inlets connect to one side

(outside iirc) of the filter element, the two ports marked as outlets connect to the other side of the filter element. I presume it has

previously worked in this configuration. The DPA pump has a feed & return.

 

I'm also pretty convinced that the "extra fitting" in the return line from the DPA pump (bottom right hand inlet to filter head) if

removed would prove to be a one way valve.

 

 

springy

Edited by springy
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On a DPA injector pump the connection furthest away from the engine block is the fuel inlet. This is because it has a strainer and regulating valve below the large flexible. The connection nearest the block is the return. This is needed because the transfer pump part of the assembly (together with the lift pump) always produces more fuel than the engine needs so the pressure build up inside the assembly is in some way proportional to speed.

 

Your engine seems to have been plumbed the wrong way round with the supply running to the pump outlet and the return to the filter outlet. The arrowheads plus the extra "hexagon thing" on one filter union gives the clue. The long hexagon thing is the non-return valve that is usually fitted in the return to the filter, not h supply so unless that valve is faulty I can not see how your engine runs properly, but I suppose it must - magic that.

 

You seem to have got it all covered but I would love to know why/how your engine runs.

 

It certainly seem that you are passing unfiltered fuel into the pump body.


On a DPA injector pump the connection furthest away from the engine block is the fuel inlet. This is because it has a strainer and regulating valve below the large flexible. The connection nearest the block is the return. This is needed because the transfer pump part of the assembly (together with the lift pump) always produces more fuel than the engine needs so the pressure build up inside the assembly is in some way proportional to speed.

 

Your engine seems to have been plumbed the wrong way round with the supply running to the pump outlet and the return to the filter outlet. The arrowheads plus the extra "hexagon thing" on one filter union gives the clue. The long hexagon thing is the non-return valve that is usually fitted in the return to the filter, not the supply so unless that valve is faulty I can not see how your engine runs properly, but I suppose it must - magic that.

 

You seem to have got it all covered but I would love to know why/how your engine runs.

 

It certainly seem that you are passing unfiltered fuel into the pump body.

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Springy,

I know what you mean about the plumbing on the filter head looking correct and I didn't think anything was amiss until I looked through a DPA pump manual. It was then that I realised, as Tony has said, that the inlet on the pump is the connection furthest away from the engine.

 

Tony,

thanks for your input. As mentioned in my original post, I am indebted to you for all the information I have gleaned from your website and as a result have only ever run my boat with the extra primary filtration you recommend.

 

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That's probably why I haven't written off the injection pump yet.

 

The fitting on the filter head has confused me as well. It will be interesting to see what it is when I get up to the boat to do the work. There's no rush as it's currently winterised.

Here is the Delphi non-return valve that I've got for the job (on the basis that if the device already on the boat is a non-return valve, it clearly isn't up to the task!) and they're different:

 

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Gentlemen, thank you.

 

Grockle

 

 

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That pump is actually built mirror image to mine, actually on a 1.8, although I thought they would be the same. The leak-off arrangement is also different. This means it appears to be connected correctly.

Arthur

 

Seeing the transfer pump and regulating valve are both at the end furthest away from the mounting flange on those DPA pumps I do not see how you could have the inlet closest to the mounting flange. However I suppose you may not have a DPA pump on it.

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  • 3 years later...

Hey guys, sorry to revive an old thread, but I think I have a related topic. My non-return valve is mounted on the main filter lift-pump inlet. Is there a reason for this, or is it incorrect? By the way, my vessel is ocean going, not a canal boat, but this forum seems the best place for info on my BMC 1.5. I have a photo, but not sure how to add it here.

 

Edit - she ran a few months ago, but with a low pressure problem, now she won't start. The spring in non-return valve was destroyed, I replaced it, but after reading this I realise that could be my problem. However, the valve in it's current position should allow fuel to flow in correct direction, but could restrict it's flow somewhat.

Edited by Captn Black
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Here is the Delphi non-return valve that I've got for the job (on the basis that if the device already on the boat is a non-return valve, it clearly isn't up to the task!) and they're different:

 

14ef768e-30c7-41f8-8678-d79969961e2b_zps

 

Gentlemen, thank you.

 

Grockle

 

Where can I purchase one of these please? Edited by Captn Black
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The lift pump works since I cleaned it. By low pressure I mean that the last time I ran it it was overreving significantly in neutral, which I was told is an issue with BMCs when air enters the fuel system, which I later found out that it was doing, through cracked injector pump return line. The line is now fixed, and through discussion on another forum I have narrowed down the main issue to the injector pump, probably caused by diesel bug.

Any tips on cleaning the injector pump gause without creating additional problems would be very welcome.

So I could potentially remove the non return valve? Does yours have two fuel filters? The valve is after the lift pump, which is after the secondary filter with water seperator.

Edited by Captn Black
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The CAV fuel system should have the non return valve is the flow back into the filter union but they usually work without it. Try your local diesel injection equipment specialist - ask as you usual garage.

 

The OUT pipe from the filter head runs into a large hexagon on the end of the injector pump. If you CAREFULLY undo the large hexagon (note spring loaded parts inside) you will find a plastic strainer. make sure this is clear.

 

I would be very reluctant to suggest that you remove the "turret" with the stop and speed lever on it so you can clean the governor valve but many have. Extreme cleanliness required for both jobs and w3ash in clean diesel before reassembly. I would rather the pump went to a specialist as timing the 1.5 is dead easy as long as the cam shaft and pump drive has not got too much wear.

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