b.m.c. fuel supply

[robmilton]

Hi all, does anyone know if a b.m.c 1800 needs a lift pump in marine use ? or will a gravity feed supply enough fuel to the injector pump to suffice ?

i ask this as i suspect my lift pump may be drawing in air and making the motor missfire, any help appreciated.

[alan_fincher]

Hi all, does anyone know if a b.m.c 1800 needs a lift pump in marine use ? or will a gravity feed supply enough fuel to the injector pump to suffice ?

i ask this as i suspect my lift pump may be drawing in air and making the motor missfire, any help appreciated.

I don't think I'd want to try operating without one.

 

That's not to say it will not, but usually engines with no lift pump use a raised "day tank" to give a better gravity feed of the fuel.

 

If you are suspicious of the lift pump, why not just replace it.

 

New ones don't cost the earth......

 

ASAP Supplies - Possible Replacement Linky

[Slim]

Hi all, does anyone know if a b.m.c 1800 needs a lift pump in marine use ? or will a gravity feed supply enough fuel to the injector pump to suffice ?

i ask this as i suspect my lift pump may be drawing in air and making the motor missfire, any help appreciated.

 

Don't know the answer to your question but why not try and sort out the root problem? If you KNOW it's the lift pump then replacement, as suggested by Alan, is the obvious route.If you're unsure where the air is getting in I suggest you disconnect the supply at an appropriate (upstream) point, shut off the tank outlet tap and gently pressurise the system with compressed air from a bike pump or similar. it helps if you can include a one way valve off an old bike inner tube. With any luck you should see bubbles even where there was no sign of fuel leakage. Had I tried this sooner it would have saved me a new lift pump, an injector pupmp and injector overhaul and who knows how many hours of work. In another situation it would have saved me lugging a new oil pump for a large Ford engine out to the Med for a friend when the problem was a leaking (internal) leakoff rail.

 

 

 

 

 

 

Frank

[musicman]

. . . and the lift pump is VERY helpful after you have changed filters etc and need to bleed the system to get the engine going again. For the sake of a few quid, I would say, change it and fit a new one.

[RLWP]

To make it more interesting, if the lift pump has failed, and you don't intend to use it, I would make plans to remove it by repiping the fuel line and blanking off the side of the engine. Otherwise, you could leave a broken pump to damage your camshaft

 

Richard

[Geoff Taylor]

Hi

 

Your BMC 1800 engine has a CAV DPA rotary injector pump and it relies on fuel pressure from either a mechanical or electric fuel pump to make it work.

 

I guess you have the mechanical lift pump fitted as standard and it may have failed,usually it will either leak diesel out of the bleed hole by the priming lever or leak into the oil sump raising the engine oil level (check dipstick).

 

A replacement part is quite inexpensive and easy to fit. Before jumping to the pump failure conclusion I would thoroughly check the fuel lines and replace the fuel filters as dirty filters can cause air to be drawn in by loose pipe joints that do not appear to be faulty. Some lift pumps have a removable lid on the top of them that have an internal gauze filter fitted ,this must be checked also. If you remove the suction side fuel line going to the lift pump and place your finger over it and press the primer lever, a definate feeling of suction should be observed for a while,if this is not felt, then the pump may well be suspect.

Hope this helps you with your problem.

[David Schweizer]

Hi

 

Your BMC 1800 engine has a CAV DPA rotary injector pump and it relies on fuel pressure from either a mechanical or electric fuel pump to make it work.

 

I guess you have the mechanical lift pump fitted as standard and it may have failed,usually it will either leak diesel out of the bleed hole by the priming lever or leak into the oil sump raising the engine oil level (check dipstick).

 

A replacement part is quite inexpensive and easy to fit. Before jumping to the pump failure conclusion I would thoroughly check the fuel lines and replace the fuel filters as dirty filters can cause air to be drawn in by loose pipe joints that do not appear to be faulty. Some lift pumps have a removable lid on the top of them that have an internal gauze filter fitted ,this must be checked also. If you remove the suction side fuel line going to the lift pump and place your finger over it and press the primer lever, a definate feeling of suction should be observed for a while,if this is not felt, then the pump may well be suspect.

Yes, I have had the engine racing phenomenon on a couple of occassions on our BMC 1.5, and each time I had left too long a period between fuel filter changes. A new filter cured the problem both times.

Hope this helps you with your problem.

 

At the time it was suggested to me that the racing might be caused by water in the filter, but when I poured the filter contents into a jar, there was no eveidence of water, so I guess it must have been caused by air being drawn in.

Edited July 18, 2011 by David Schweizer

[Tony Brooks]

Yes, I have had the engine racing phenomenon on a couple of occassions on our BMC 1.5, and each time I had left too long a period between fuel filter changes. A new filter cured the problem both times.

Hope this helps you with your problem.

 

At the time it was suggested to me that the racing might be caused by water in the filter, but when I poured the filter contents into a jar, there was no eveidence of water, so I guess it must have been caused by air being drawn in.

 

 

Don't know if this helps but the 1.5 & 1.8 use a hydraulically governed injector pump. The injector pump has it's own "intermediate pressure pump" (transfer pump) in it plus a regulating valve. As far as I can see the pressure in the pump is proportional to pump shaft and thus engine speed.

 

The governor itself consists of a spring that is preloaded by the throttle lever trying to open the governor valve and a small piston that is subject to the pressure in the pump body trying to close the governor valve.

 

In operation the governor valve is held in a particular position by the interaction of the hydraulic and spring pressure.

 

It seems that if there is ANY form of fuel supply restriction the transfer pump pressure drops, allowing the spring to open the governor valve. Providing there is still some transfer pressure in the pump this seems allow more fuel to "get through" governor valve allowing the engine to rev.

 

It is probably more often a matter of blocked filters than anything else but remember ANYTHING that causes a drop in transfer pump pressure seems to allow the engine to rev.

[robmilton]

Thanyou for all the replies, i have ordered a new lift pump and filter and will pop them on at the weekend and give it a run, fingers crossed .

Rob.

[Tony Brooks]

Thanyou for all the replies, i have ordered a new lift pump and filter and will pop them on at the weekend and give it a run, fingers crossed .

Rob.

 

 

Make sure that you slide the operating lever up the inside face of the engine block. It is all too easy to get it on the wrong side of the camshaft and then use a bit of force to tighten the fixing nuts home - this wrecks the new pump!

[robmilton]

Make sure that you slide the operating lever up the inside face of the engine block. It is all too easy to get it on the wrong side of the camshaft and then use a bit of force to tighten the fixing nuts home - this wrecks the new pump!

 

 

Thanks Tony, will do.

[bizzard]

To make it more interesting, if the lift pump has failed, and you don't intend to use it, I would make plans to remove it by repiping the fuel line and blanking off the side of the engine. Otherwise, you could leave a broken pump to damage your camshaft

 

Richard

Also some of those engines have the Lucas DPA rotary injector pump which are quite fussy about being run other than the standard set up,Temperamental,and they're expensive. If you have the older CAV inline pump,much more robust and forgiving,so would be worth a try at gravity feed,but i'd keep tank as close to the injector pump as pos,higher of course and no loops or U bends,just straight down to the engine from bottom of tank. bizzard

[robmilton]

Well !!!! i ran the boat for about an hour on gravity feed and it was fine but still missfiring and a little smokey, i have now fitted a new lift pump and the difference in both starting and running is very noticeable, the missfire and smoke have completely dissapeared.

So.... a bmc with c.a.v rotary pump WILL run on gravity feed to get you home but DOES need a lift pump to perform at its best, hope this may help someone for future reference, thanks all for your replies.

[alan_fincher]

And thank you for closing off the story.....

 

It is always good to hear both a successful outcome, but also to learn whether the theory proved right in practice!

[Tony Brooks]

And thank you for closing off the story.....

 

It is always good to hear both a successful outcome, but also to learn whether the theory proved right in practice!

 

 

Well, I think we were fed a bit of dodgy theory. The DPA pump relies on pressure from the transfer pump to operate. This pump is in the end of the injector pump so is not dependant upon the lift pump. I accept it may not self bleed very will but as long as there is minimal restriction in the gravity feed and the pipes allow a sufficient flow of fuel I am not surprised it worked under gravity. The regulating valve which sits between the inlet and transfer pump may make it difficult to get fuel into the pump if the head is insufficient but it is designed to "get out of the way" when bleeding via the lift pump. If there is a gravity problem my suspicion is that the head would be insufficient to push the valve out of the way.

[RobinJ]

Well, I think we were fed a bit of dodgy theory. The DPA pump relies on pressure from the transfer pump to operate. This pump is in the end of the injector pump so is not dependant upon the lift pump. I accept it may not self bleed very will but as long as there is minimal restriction in the gravity feed and the pipes allow a sufficient flow of fuel I am not surprised it worked under gravity. The regulating valve which sits between the inlet and transfer pump may make it difficult to get fuel into the pump if the head is insufficient but it is designed to "get out of the way" when bleeding via the lift pump. If there is a gravity problem my suspicion is that the head would be insufficient to push the valve out of the way.

It will not be something you can rely on too much...

There will be sufficient pressure on most systems with a full tank as there is likely to be at least a foot of head (possibly?), but if the tank is low or there is an old filter which reduces flow etc., then the pressure may not be sufficient?