A "bleeding"problem

[Jim@sea]

Normally I am quite good at bleeding Diesel engines and getting them running.
But the engine in the boat I have recently bought has me beaten and I have run out of ideas.
It is a BMC Diesel 2.5l. 1984.
There was a problem when I bought the boat as on a sea trial the engine broke down and we had to be towed back.
But for the 5 minutes it did run it sounded fine. (I did have a garage for 25 years and listening to engines was part of my job)
I bought the boat and have probably done things the wrong wayround, I had a "cold" compression test and the compressions were very good, but instead of getting the engine running properly then improving it I have had the injectors serviced and new glow plugs then tried to start it.
I can get it running, then after 5 minutes it stops. Slacking off the injector nuts and turning the engine over shows not enough fuel.
I have fitted 2 new CAV filter housings and a new Lift Pump.
Should I now buy an Electric Pump and plumb it in, as then the pressure is constant and should there be the slightest gap which would allow air to be sucked in it would leak out.
To get the injector pump out requires an engine removal so that is my last resort.
The only other thing that I can think of is that although I drained both tanks I only refilled one, but they share the same on/off switch, I had assumed that by filling one it would drain down to the on/off switch and continue upwards filling the empty tank until both tanks are at the same level.
BUT if this was the case why would there be 2 fuel gauges, as, if by filling one it filled both, then the gauges would read the same. So at the moment when I start the engine when running the pump could be sucking from both tanks, ie one with fuel in and one which has been emptied so its getting air in from an empty tank.
What would a professional do next,
ALL SUGGESTIONS GRATEFULLY RECEIVED.
PS. 30 years ago I had a boat with 2 tanks but you could choose which one to use by a switch on each tank. this one only has a single on/off switch. fed by 2 pipes.

 

[Graham_Wright]

This might help;-
http://www.ybw.com/forums/showthread.php?395208-Engine-YAPP

 

[fisherman]

Install a separate ball valve for each tank.

 

[Jean]

Think I'd want independant control of each tank feed rather than a common valve, but of course need to check where the diesel return feeds back in relation to tanks first. Presume lift pump has manual operation lever too, in which case, with injector end of pipe loosened, or injector bleed opened, and lift pump operated, will indicate if enough fuel getting through, in which case no gain from an electric pump. Just been working on daughters BMC 1.8 boat engine, same vintage, and a new (exchange) CAV injector govenor has made a world of difference in performance (old one was leaking).
Are you sure it is an on/off switch and not a tank selector switch without an off position as sounds a bit odd?

 

[Daydream believer]

Part fill both tanks then see what happens as the pump will not suck air from either tank. Or if it does there is an issue in the tanks - like pipe end dropped of so not sucking from low down

 

[bikedaft]

Jerry can, hose to filter, as a temp tank?

 

[vyv_cox]

If it runs well for five minutes and stops you can rule out the injection pump and almost certainly the lift pump. One possibility is that the tank(s) is not venting - this would be a very typical symptom. Can you rig a temporary tank, just a plastic bottle, to identify tank problems?

 

[fisherman]

So you are drawing fuel from two tanks, if one tank has different pressure or lack of it then it will empty and air will draw, and when you stop the engine fuel will drain to it from the other and fool you into thinking it's not been empty. Run the engine with a syphon from a bottle above it, or an outboard tank, if it runs OK this is the problem.

And, (edit), if the return goes to one tank the other will empty first, as above.

 

[bikedaft]

And, (edit), if the return goes to one tank the other will empty first, as above.

Good point, where does the return go? How does that "normally" work with a two tank set up?

 

[Caer Urfa]

Hi Jim

I think the clue maybe in that you say you have fitted new filters and pump.

I did that years ago and suffered the consequences for months when my engine would run for 8 hrs then stop dead.

Cutting a very long sad story short have you got the filters below the level of the tanks, ie so they are gravity fed??
Have you increased the distance from the filters to your lift pump??

Thats the mistake I had made, the filters I had re-mountd were 'above' the bottom of the tanks, and further away from the pump.

The results was the pump just could not pump enough the distance of the new pipework and the filter position did not help.

I then remounted the filters BELOW the level of the tanks AND moved them towards the lift pump, never had a problem since!!

Hope this might be 'food for thought'.

Regards
Mike

 

[Jean]

One option for 2 tank systems is for the return to go into a common feed point, like the water seperator/course filter.

 

[fisherman]

One option for 2 tank systems is for the return to go into a common feed point, like the water seperator/course filter.

Oh no. Been there done the whole day trying to get back home. You get an air leak in the return, air straight back to the injector pump, even if your engine is self purging you have an endless feed of air. Return to the tank, no problem.

 

[Jim@sea]

Think I'd want independant control of each tank feed rather than a common valve,
Are you sure it is an on/off switch and not a tank selector switch without an off position as sounds a bit odd?

I enclose a photo of the switch which shows the two incoming supply fuel lines with one leaving.
The lever is either on or off. If I slacken off a filter connection when switched "on" I get fuel coming through. I suppose really I should have slackened both pipes off at the switch to ensure that fuel was flowing. its hard to reach, it must have been installed before the engine.
Could this fuel switch have "non return valves" as that would explain why the fuel was not going from 1 tank to the other and when running the pump was then sucking air from the empty tank.

Fortunatly both tanks are above the switch and filters etc.
The diesel return goes back to the top of the second filter.

 

[bikedaft]

plenty compression fittings there to loosen just slightly - enough to let in air.

 

[vyv_cox]

Don't make any assumptions about that type of valve. I have one on my water heating system and it does not do what might be expected from the handle position.

There is no check valve in your photograph.

 

[Graham_Wright]

Hi Jim

utting a very long sad story short have you got the filters below the level of the tanks, ie so they are gravity fed??
Have you increased the distance from the filters to your lift pump??


The results was the pump just could not pump enough the distance of the new pipework and the filter position did not help.

I then remounted the filters BELOW the level of the tanks AND moved them towards the lift pump, never had a problem since!!

Hope this might be 'food for thought'.

Regards
Mike

That's interesting. My filters are high (tanks are in the keels so no alternative). But the engine lift pump is only around 300 mm above the tank fuel level. Does that not reduce the head to 300 mm rather than the 700 mm to the filter height?

 

[vyv_cox]

That's interesting. My filters are high (tanks are in the keels so no alternative). But the engine lift pump is only around 300 mm above the tank fuel level. Does that not reduce the head to 300 mm rather than the 700 mm to the filter height?

I guesss that the majority of cars on earth have the fuel tank lower than the lift pump and the filter above the pump. A diaphragm lift pump will easily cope with a couple of metres of lift.

 

[Bilgediver]

I enclose a photo of the switch which shows the two incoming supply fuel lines with one leaving.
The lever is either on or off. If I slacken off a filter connection when switched "on" I get fuel coming through. I suppose really I should have slackened both pipes off at the switch to ensure that fuel was flowing. its hard to reach, it must have been installed before the engine.
Could this fuel switch have "non return valves" as that would explain why the fuel was not going from 1 tank to the other and when running the pump was then sucking air from the empty tank.

Fortunatly both tanks are above the switch and filters etc.
The diesel return goes back to the top of the second filter.

That looks like a selector valve. Possibly can select either tank or both and off. Sometimes the end of the spindle shows how the port is arranged. This could be a 90 degree port or a Tee shaped port in the valve plug. It could be you have just been turning one of the tanks on and off.

How many degrees does the handle swing through???

Which pipes go where ? Normally the side pipes would be to tanks and the lower one to engine.

If the spindle is tee ported then in the position shown if pipes as I indicated then both tanks are selected. IE

Handle down selects both tanks

Handle to left selects left tank.

Handle to right selects right tank

Handle up turns fuel off engine but balances tanks.

 

[Caer Urfa]

That's interesting. My filters are high (tanks are in the keels so no alternative). But the engine lift pump is only around 300 mm above the tank fuel level. Does that not reduce the head to 300 mm rather than the 700 mm to the filter height?

Hi Graham

I think my problem was apart from originaly mounting the two filters 'too high'(above the bottom of the fuel tanks I also moved them away from the lift pump (about another 300mm) my idea was for easier access to them but assume now that the lift pump could not cope with the extra distance and maybe the re-positioned filters were also adding to the problem, as said I moved them lower and closer to the fuel lift pump.

As you can see in the picture attached I have the filters as low as possible and the lift pump is in line with the top yellow fuel hose (starboard side)..

You can also see my changeover fuel valve is also in line with the filters (just above the gearbox) BUT, I do not leave the handle on as it once came off at sea and thank heavens it missed the spinning flexable coupling, never had any problems with the system now and can run off 'either' tank, or 'both' tanks, I also 'if necassary' can divert the return fuel to either tank.

Mike

View attachment 42241[

 

[Jim@sea]

That looks like a selector valve. Possibly can select either tank or both and off. Sometimes the end of the spindle shows how the port is arranged. This could be a 90 degree port or a Tee shaped port in the valve plug. It could be you have just been turning one of the tanks on and off.

How many degrees does the handle swing through???

Answer: The handle only swings 90 degrees.
Which pipes go where ? Normally the side pipes would be to tanks and the lower one to engine.
Answer: The side pipes are from each tank and the lower one feeds the lift pump.

If the spindle is tee ported then in the position shown if pipes as I indicated then both tanks are selected. IE

Handle down selects both tanks

Handle to left selects left tank.

Handle to right selects right tank

Handle up turns fuel off engine but balances tanks.

Answer: With this handle (in the position shown on the photo) the valve/switch is "off" (which hopefully explains why on a sea trial the boat broke down as the person who took me out may have thought that in this position the fuel valve was open) (And it only takes a second with a marker pen to mark the position)
When the handle is turned to the right I have fuel. The switch does not turn to the left.
Hopefully later in the week I will have fitted a switch for each tank leading to a single "off switch" I will have cleansed and blown through each pipe and re-located the switches to where they can be reached. And established if there is a Non Return Valve preventing one tank from gravity feeding the other.
Its a bit like the Mensa challenge.