cant bleed the fuel lines - normally no problem

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Airscrew

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MD11c.
Had the injectors serviced.
They were off the boat for 4 weeks.
I cant bleed the lines to the injectors using the lift pump.
Pumping many times (say over 100), and with the crank/flywheel in various positions, produces no fuel from the (cracked) injector nuts.
I've changed both filters and bled through without problem before.
Filters were changed and bled, and engine oil changed in January, and engine ran fine after that.
Re-bled both filters today, OK, but to no effect.

The odd thing is, when the injectors were out, and also today with the injectors in but the decompression levers 'open', turning the engine over by hand DOES produce a short 'pulse' of fuel from both injector nuts at the appropriate point of the cycle.
But Then immediately trying the lift pump produces nothing.
Spinning the engine on the starter, with the injector nuts well cracked is not conclusive, as singled handed I c ant turn the key and see the engine. However, kitchen paper did NOT reveal a soaking of diesel.


For the hell of it, I connected it all up and cranked it over for 10 or 15 secs, a few times with gaps inbetween.
No joy, and time to return for supper.
Battery is nearly new, and 13.2.
Starter motor speed and engine rotation were good and normal.

Nothing else has changed since it last ran, other than injectors serviced.

Do I suspect the lift pump or injector pump?
Or do I just take a booster battery down and have more patience on the starter??
 
Airscrew said:
MD11c.
Had the injectors serviced.
They were off the boat for 4 weeks.
I cant bleed the lines to the injectors using the lift pump.
Pumping many times (say over 100), and with the crank/flywheel in various positions, produces no fuel from the (cracked) injector nuts.
I've changed both filters and bled through without problem before.
Filters were changed and bled, and engine oil changed in January, and engine ran fine after that.
Re-bled both filters today, OK, but to no effect.

The odd thing is, when the injectors were out, and also today with the injectors in but the decompression levers 'open', turning the engine over by hand DOES produce a short 'pulse' of fuel from both injector nuts at the appropriate point of the cycle.
But Then immediately trying the lift pump produces nothing.
Spinning the engine on the starter, with the injector nuts well cracked is not conclusive, as singled handed I c ant turn the key and see the engine. However, kitchen paper did NOT reveal a soaking of diesel.


For the hell of it, I connected it all up and cranked it over for 10 or 15 secs, a few times with gaps inbetween.
No joy, and time to return for supper.
Battery is nearly new, and 13.2.
Starter motor speed and engine rotation were good and normal.

Nothing else has changed since it last ran, other than injectors serviced.

Do I suspect the lift pump or injector pump?
Or do I just take a booster battery down and have more patience on the starter??
Click to expand...

Th lift pump doesnt pump fuel through the injectors, it lifts it to the injection pump which then pumps it under high pressure to the injectors! So pumping the lift pump, you wont ever see any coming out of the injector pipes!
 
Firstly make sure there are no air leaks. Its easy if you have changed filters to not have seated the seal properly so that operating the pump just sucks air. Crack the bleed screw on the primary filter. If in doubt remove it completely. Then when you pump you should get fuel out of the screw hole. If you don't you probably have a problem between tank and engine. If you do replace screw and turn over engine. Only when you turn engine over will you get fuel to the injectors. Unless the fuel pump is turning over you won't by just operating lift pump. The lift pump delivers fuel to the fuel pump. The fuel pump delivers to the injectors. Hope this is clear.
 
Thanks to all for this.

I can (and do) read the workshop manuals, and search online, but just a couple of paragraphs from you good people, and I now have a clear picture of how things work, and what to do.

Once this gale has blown through, I will go down tomorrow, and work through all those tips.
Thanks again.
 
Have now looked closely at the schematics on marinepartseurope.
https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742230-23-15118.aspx

You will know or understand that on a Centaur, the ability to clearly see all the components in situ is reserved for very small people or contortionists.
For me and others, most of this work is done by touch not by sight :)

So the flow goes from tank, primary filter, lift pump, secondary filter, injection pump (HP), injectors.
Also, I didnt realise that there is a HP bleed screw on the injector pump.
Part 21 on the injector pump schematic
https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742230-23-15122.aspx
I guess I hadnt needed it previously.

Q.
Can the lift pump lever bleed the HP injector bleed screw, or can I only do that with the engine turning?.
That would require two people...
 
On my MD7 the lift pump pushes fuel as far as the bleed screw on the injector pump, but no further. As with any mechanical injection pump, any air in the pump body will simply be compressed rather than pressurising the fuel. Self priming pumps (I have one in my van) have an internal lift pump which expels air via the injector leak off line. Volvo didnt make anything so clever sadly. Would have saved a few boats over the years if they had!
 
Airscrew said:
Have now looked closely at the schematics on marinepartseurope.
https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742230-23-15118.aspx




Q.
Can the lift pump lever bleed the HP injector bleed screw, or can I only do that with the engine turning?.
That would require two people...
Click to expand...
Yes, operating the lift pump lever will bleed the fuel to the bleed screw on pump. This should be the last place you bleed with the lift pump. Once all air is expelled, turn the engine over on starter with injector unions loosened until you see diesel spitting from the pipes. Tighten unions and see if it starts.
 
Airscrew said:
Q.
Can the lift pump lever bleed the HP injector bleed screw, or can I only do that with the engine turning?.
That would require two people...
Click to expand...
A
HP bleed is for what it says HIGH pressure so you have to bleed with the engine.
I manage mine on my own by wrapping toilet paper around the bleed point so I can see when fuel is coming out, then I nip it up and move on to the next point.
 
LadyInBed said:
A
HP bleed is for what it says HIGH pressure so you have to bleed with the engine.
I manage mine on my own by wrapping toilet paper around the bleed point so I can see when fuel is coming out, then I nip it up and move on to the next point.
Click to expand...
Blue paper towels make an even better indicator. Can also be used to detect leaks aroud skin fittings. Find some place that fill their towel dispensers with blue towels and purloin a few.
 
Strange, looking at the previous comments, but I have no problem pushing fuel and air through to the injectors with the lift pump lever on my Sole Mini 34. I'm starting to feel inadequate now.
 
I believe some people are mistaking the injection pump with the injectors. You bleed with the lift pump to the injection pump, after that it is high pressure (hence the steel pipes and unions) to the injectors. To bleed to the injectors you need the engine turning over with the injector pipe union slackened at the injector until you see the fuel spitting from the pipe. If on your own you will have to wrap a cloth or towels around the injectors until the towel is wet with diesel. The delivery valves in the injection pump should prevent any diesel from passing the pump when using the lift pump, you can't generate the pressure needed.
 
black mercury said:
I believe some people are mistaking the injection pump with the injectors. You bleed with the lift pump to the injection pump, after that it is high pressure (hence the steel pipes and unions) to the injectors. To bleed to the injectors you need the engine turning over with the injector pipe union slackened at the injector until you see the fuel spitting from the pipe. If on your own you will have to wrap a cloth or towels around the injectors until the towel is wet with diesel. The delivery valves in the injection pump should prevent any diesel from passing the pump when using the lift pump, you can't generate the pressure needed.
Click to expand...

I know the difference between the injector pump and the injectors.
 
Have been away for a number of weeks.
Was on the boat today, and I believe I still have a problem bleeding the system.

I have easily bled the primary filter, and the secondary and top of the injector pump (part 21 here) https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742230-23-15122.aspx
And bled at the injectors with a cloth and spinning the engine.
I also bled the return side, which did produce air and bubbles, and then was completely bled successfully (I have learnt that on an MD11 the return is back to the 2nd filter, not to the tank).

But I found something that I think is a surprise to me.
After still not starting, I rechecked the return side. On cracking one return union at the injector (engine NOT spinning), there was a quantity of fuel released under pressure, spraying more than a foot. I could repeat this on the other injector after spinning the engine again.
But if I crack either injector union on the supply side (again engine NOT spinning), I do NOT get this pressure spurt.

This appears to suggest there is pressure on the return side but not the supply side...???

Is this right/normal, or is this indicative of a/the problem?

Many thanks for any guidance here...
 
Airscrew said:
Have been away for a number of weeks.
Was on the boat today, and I believe I still have a problem bleeding the system.

I have easily bled the primary filter, and the secondary and top of the injector pump (part 21 here) https://www.marinepartseurope.com/en/volvo-penta-explodedview-7742230-23-15122.aspx

But I found something that I think is a surprise to me.
After still not starting, I rechecked the return side. On cracking one return union at the injector (engine NOT spinning), there was a quantity of fuel released under pressure, spraying more than a foot. I could repeat this on the other injector after spinning the engine again.
Click to expand...
This would lead me to think that there was a bubble of air in this part of the circuit.

Ash
 
Seems like you have almost tried everything. I have in the past experienced a similar problem and one that doesn't happen very often. This is the failure of the fuel pump itself to free the trapped air in the barrel . The solution to this is to loosen the delivery valve on each pump just a turn or so after first loosening the attached injector pipe and then pump the lift pump a few times before winding the engine on the starter. You should see fuel coming from the loose threads of the delivery valve once the air is released and then tighten the delivery valve and injector pipe. Only one of my pumps needs this treatment from time to time but in your case both of the pumps may be airlocked.

Don't forget to have full throttle and cold start for this.
 
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