Anoying fuel problem...Grrrrr!

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The Dogs Pollacks Brother

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Can't fathom this one out so will throw it to you guys.
We have an old BMC 1.5 engine on the Grumpy Uncle, but since we are back in the water after winter we have had a problem starting her. Last season she would start a treat but this year.........not so. We give the engine some heat as we have always done and she winds over and trys to start. Just another 3 or 4 seconds and she would normaly be away, but it just trys to fire then stops trying and just winds over. It appears as if we use up all the fuel in the injection pump then she is trying to start on fresh air. We then have to bleed at the banjo on the pump as we pump the plunger on the cav filter. We then loosen off an injector nut and crank again and off she will go. It will then start ok for the next 24 hours over any period of time...i.e....in the next hour, or 4 hours later, 12 hours later ect, but after a full 24 hours we have to do it all again, but not as drastic as to crack off the injector nut. Leave it a week and its the full job again.
I am guessing...rightly or wrongly...that the issue is not on the high presure side of the pump as surely we would see or smell fuel squirting somewhere?
Also, when we bleed at the banjo on the pump we see air in the system so the problem must be between the fuel tank and the injection pump?
The system is as basic as it can be.... fuel tank.......cav filter with plunger on top........pump on side of engine with little primer rod......filter.....injection pump.
All we have done is change the 2 filters so the finger points here but I am at a loss as to where exactly. O rings seem ok and fitting nice, and the fact that she does'nt draw in air or cough and splutter while under way just makes it all the more confusing.
Over to you guys....and thanks for reading.
Jeff
TDPB.
 
Air in fuel from the filter change is likely often copper washers don't like being disturbed

Also worth checking that the start plugs don't have a carbon build up requiring reaming out with drill bit 9/32 maybe check this size .
 
Thanks for the quick reply Scottie..........the fact that we have to bleed it AND see the air we are bleeding makes me think the problem is here and not at the heater plugs. Having said that, if its an easy job to do, it may well be worth looking at them too?

Mmmm...copper washers....will check next time we are there.

Thanks again.
 
We had v similar symptoms although not quite as severe - in our case we had to have been at sea for a few days before it wouldn't start without re-priming / bleeding.

The cause turned out to be a small leak after the lift pump, ie on the secondary filter. This allowed air to get back into the fuel system when the engine was stopped, but wasn't sufficiently severe for fuel to be seen leaking out. If only a bit of air had got in then the lift pump was still primed and the engine would start and run, but if the fuel level had fallen below the lift pump then the system would need bleeding again before it would start. This was time dependent.

The leak was not actually from the seating of the filter element but the small 'O' ring (~6mm ID) on the bleed screw. There is also a similar 'O' ring in the CAV filter's central bolt. Neither seem to be supplied new with replacement filter elements so are often not changed during a service, but should be imho.
 
The Dogs Pollacks Brother said:
Can't fathom this one out so will throw it to you guys.
We have an old BMC 1.5 engine on the Grumpy Uncle, but since we are back in the water after winter we have had a problem starting her. Last season she would start a treat but this year.........not so. We give the engine some heat as we have always done and she winds over and trys to start. Just another 3 or 4 seconds and she would normaly be away, but it just trys to fire then stops trying and just winds over. It appears as if we use up all the fuel in the injection pump then she is trying to start on fresh air. We then have to bleed at the banjo on the pump as we pump the plunger on the cav filter. We then loosen off an injector nut and crank again and off she will go. It will then start ok for the next 24 hours over any period of time...i.e....in the next hour, or 4 hours later, 12 hours later ect, but after a full 24 hours we have to do it all again, but not as drastic as to crack off the injector nut. Leave it a week and its the full job again.
I am guessing...rightly or wrongly...that the issue is not on the high presure side of the pump as surely we would see or smell fuel squirting somewhere?
Also, when we bleed at the banjo on the pump we see air in the system so the problem must be between the fuel tank and the injection pump?
The system is as basic as it can be.... fuel tank.......cav filter with plunger on top........pump on side of engine with little primer rod......filter.....injection pump.
All we have done is change the 2 filters so the finger points here but I am at a loss as to where exactly. O rings seem ok and fitting nice, and the fact that she does'nt draw in air or cough and splutter while under way just makes it all the more confusing.
Over to you guys....and thanks for reading.
Jeff
TDPB.
Click to expand...

Sounds familiar http://www.ybw.com/forums/showthread.php?355548-Diesel-engine-slow-to-fire
 
Hi Jeff

I spent hours and hours one year trying to find the problem, may be a wild guess but is your starter motor ok? it was the problem on mine and the last thing I would have thought of checking !!

Also have you moved the fuel filters when ashore??

Also check all your fuel joint connections as you may be sucking in air just from one joint.

Mike
 
jdc said:
The leak was not actually from the seating of the filter element but the small 'O' ring (~6mm ID) on the bleed screw. There is also a similar 'O' ring in the CAV filter's central bolt. Neither seem to be supplied new with replacement filter elements so are often not changed during a service, but should be imho.
Click to expand...

I changed the elements on both my cav filters with really cheap mann elements from the motor factor (circa 2 quid each) and each element still came with a complete new set of seals including the O ring. what brand of filter are you using and where are you getting them from? you should always change the seals when you change the element.

back to the OP, it does sound like shes sucking air in. I had an old diesel volvo v40 that would die under load. took it to volvo no idea they wired up all the diagnostics. finally called the RAC and the guy knew what it was before he even saw it. common fault on the V40 was a hairline crack in the fuel filter housing, somehow small enough to let air in but no fuel leaks out. new housing and hey presto-fixed. If you could substitute a clear length of fuel hose downstream of your filter but before the HP pump just for diagnostics I'll bet you'll see tiny bubbles. then when you stop it these pool to form an airlock.

as for finding the leak. thats a bit of detective work on your part! good luck! but for the cost I'd start with a new set of filters WITH new seals. some new copper washer on the banjos wont hurt either ;)
 
perhaps it is the fuel lift pump either the diaphragm or the none return valves, I don't think it's an obvious leak as you know what your doing

mick
 
Make sure your fuel pipes are not restricted and do you have a fuel return to tank or back to filter housing.make sure the pipe is not restricted as these can have hard to find faults otherwise i would put a better set of filters in.
 
Thanks for all the replies guys....plenty of good input and much appreciated.

Chaktoura.....very similar symptons indeed...thanks for the heads up!

Caer ....starter is A1 and the engine turns over fine, especialy when we "combine" the 2 batteries so happy with that. Also no pipes were removed or filters moved.

Contessaman.....will be changing the filters when I am there next and will be inspecting ALL the washers/o rings ect on the old and new.

MTB.....never thought of the lift pump being the problem as it will run and start faultlessly when bled.

Dingdongs...fuel pipes are all unrestricted and fuel is returned via the top of the tank.

Just to re-cap then..........on first cranking it almost starts,i.e,its fireing up a bit(as a cold old bmc does!) but stops fireing after a few seconds as the fuel in the injector pump and lines has been replaced by too much air. We 100% see air bubbles from the banjo bleed screw on the pump when we pump the plunger on the cav filter. It DOES NOT suck air in when running and runs as sweet as......over 3 hrs run at 5-7kts and didnt miss a beat.....which is the baffling bit to me. Leave it a day or 2 and we have to re-bleed, but ok within a 24-48 hr period.....

Many thanks again

Jeff
TDPB
 
The Dogs Pollacks Brother said:
We 100% see air bubbles from the banjo bleed screw on the pump when we pump the plunger on the cav filter.
Click to expand...

That doesn't necessarily mean the leak is in the filter - it could easily be leaking air in at the banjo. A tiny leak wouldn't be noticeable in normal running, but would allow enough air in over 12-24 hours to make starting difficult. In general, you should only bleed where there's a bleed screw; does the fuel filter on the engine have a bleed screw? Banjo bolts are best left undisturbed.
 
Not 100% sure re the bleed screw on the engine mounted filter...will check.
Perhaps I am getting my terminology confused pvb.........it is a small (6 or 8mm I think) screw we undo on the side of the injector pump I am calling a banjo? There is no pipe work connected to it, just this small screw with a little hole in it that lets air and fuel out when we bleed? **** desription I know sorry!
So it is quite possible then that a small leak wouldnt show up under running pressures or indeed suck air in under running presures but may let air in when stood for a period of time?
 
The Dogs Pollacks Brother said:
Not 100% sure re the bleed screw on the engine mounted filter...will check.
Perhaps I am getting my terminology confused pvb.........it is a small (6 or 8mm I think) screw we undo on the side of the injector pump I am calling a banjo? There is no pipe work connected to it, just this small screw with a little hole in it that lets air and fuel out when we bleed? **** desription I know sorry!
So it is quite possible then that a small leak wouldnt show up under running pressures or indeed suck air in under running presures but may let air in when stood for a period of time?
Click to expand...

What you describe sounds like a standard 'bleed screw' I would look at the connections of your pipework that delivers the fuel to the pump especially any 'jubilee clip' connections and the connection to/from your fuel filter.

Other food for thought is :
Is your fuel pump gravity fed? IE is it lower than your tank?? is the filter a long way from the fuel pump, as if it is the fuel pump may not be big enough to suck the fuel through and you may need to consider moving it nearer the lift pump.

I assume you have clean internal pipework and nothing starving fuel by blockage.

Mike
 
Ok thanks again everyone. This is pointing more and more at a dodgy filter replacement I think......after all, they were the only things in the whole fuel system changed or touched. I didnt see them changed myself as I was away at the time so cant comment on the job done, but the same guy has done them all before with no such issues a few times. For the sake of the few quid they cost I think I will make this my first point of investigation and replace them both.
Jeff.
 
The Dogs Pollacks Brother said:
So it is quite possible then that a small leak wouldnt show up under running pressures or indeed suck air in under running presures but may let air in when stood for a period of time?
Click to expand...

I suspect the leak is there all the time. I think the tiny little bubbles that the system copes with when running will be 'pooling' once stopped to form a larger bubble big enough to form an airlock. Think of a pint of guiness settling and thats what I think is causing you the trouble when you stop it.

In fact thats a great excuse for you to go to the pub tonight and have a pint of guiness! keep ordering more pints and contemplate your fuel system as you watch the tiny bubbles.....
 
Sounds similar to a problem I once had, the problem only showing after a rest. I traced it to two leaks between the lift pump and the injector pump. One let fuel out, one let air in. Once running there was no problem because the pipe was under pressure.
 
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