Yanmar 4LHA-STZP engine troubleshooting question

salar said:
Could a faulty lift pump allow air in? The engineer claims to have done a vacuum test on the hoses. The odd thing about this is that it will run for a few minutes fine, then it all goes wobbly. I would have thought a leak was a leak, or a blockage was a blockage.
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Not refering to air in the fuel, I mean make sure the engine is getting enough air into the cylinders, the "experts" had my mate remove the injector pump and re calibrated injectors overhauled, and all of it to no avail, I kept shouting AIR AIR, when he eventually removed the charge air can and removed the cooling matrix it was blocked, therefore reducing the amount air able to get into the cylinders. Think of it as a water tank and the cylinders as basins, the water is under pressure and wants to get out, the valves is opened and the pressure forces water into the basin, but if the pipes are clogged up the force is reduced, substitute this for a turbo pushing air into a tank which is pressurised, and the only was out is via the valves in the cylinder head, the cylinder is expecting a large inrush of air to match the fuel input but does not get enough because the "tank" has little or nothing to give, hence the engine loses power. Are you sure you do not have any black smoke?
 
No black smoke seen either before or at the time of the fault. The problem cuts in quite suddenly, but the engine starts again ok if a bit lumpy initially. We'll go through a process of elimination by looking at those suggestions, thank you!
 
omega2 said:
Not refering to air in the fuel, I mean make sure the engine is getting enough air into the cylinders, the "experts" had my mate remove the injector pump and re calibrated injectors overhauled, and all of it to no avail, I kept shouting AIR AIR, when he eventually removed the charge air can and removed the cooling matrix it was blocked, therefore reducing the amount air able to get into the cylinders. Think of it as a water tank and the cylinders as basins, the water is under pressure and wants to get out, the valves is opened and the pressure forces water into the basin, but if the pipes are clogged up the force is reduced, substitute this for a turbo pushing air into a tank which is pressurised, and the only was out is via the valves in the cylinder head, the cylinder is expecting a large inrush of air to match the fuel input but does not get enough because the "tank" has little or nothing to give, hence the engine loses power. Are you sure you do not have any black smoke?
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Good point.

Page 51 details washing the turbocharger blower at 250 hour intervals - http://global.yanmar.com/product/ma...ion/operationmanual/4LHA_OPM_49961-205434.pdf
 
Check the obvious first, fuel filter condition, inspect for air being pulled in, obstruction in the pick up line, dirty air filter etc.

I had a similar one on my port engine normal rpm 2500 running fine, then it would drop to 1500, surge to 2000 and then after a while clear itself, I had one of these miracle bug buster inline gadgets basically an aluminium cylinder in the fuel line before the Fuel filter with a spring in it holding several disc magnets, the cylinder/spring/magnets were blocked with a bit of fuel bug, some hair, swarf and other debris.
 
Thanks for that, and we will look at the air intake. Fuel pipes are airtight according to a vacuum test, and filters are pristine. No evidence of gunge in the tank, and in fact the pickup tube has side holes as well as an end hole so it would be difficult to block with a lump of debris. The odd thing is the problem cuts in suddenly but not predictably, so it is as if something sticky gives way at a pressure point. I will check the tank vent but it did the same thing at the same time after starting when the tank was a quarter full as when brimming full. I would expect a breather problem to kick in very quickly on a brim full tank but it is definitely worth checking, thanks.
 
salar said:
Thanks for that, and we will look at the air intake. Fuel pipes are airtight according to a vacuum test, and filters are pristine. No evidence of gunge in the tank, and in fact the pickup tube has side holes as well as an end hole so it would be difficult to block with a lump of debris. The odd thing is the problem cuts in suddenly but not predictably, so it is as if something sticky gives way at a pressure point. I will check the tank vent but it did the same thing at the same time after starting when the tank was a quarter full as when brimming full. I would expect a breather problem to kick in very quickly on a brim full tank but it is definitely worth checking, thanks.
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It stops because it has run out of breath!!
 
Well I think we have found it. The boat ran fine with hoses direct to a can of fuel so the engineers decided to replace the hoses. As they uncoupled the hose, a long string of what they describe as a silicone type substance came out, which sounds a lot like a length of PTFE tape to me, which was blowing straight when the pipe was blown through but bunching up when the pump sucked fuel. I hope a serious sea trial at the weekend will prove conclusively that all is now well. Thanks everybody for all the suggestions, I will certainly bear them all in mind if I ever have another similar problem.
 
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salar said:
Well I think we have found it. The boat ran fine with hoses direct to a can of fuel so the engineers decided to replace the hoses. As they uncoupled the hose, a long string of what they describe as a silicone type substance came out, which sounds a lot like a length of PTFE tape to me, which was blowing straight when the pipe was blown through but bunching up when the pump sucked fuel. I hope a serious sea trial at the weekend will prove conclusively that all is now well. Thanks everybody for all the suggestions, I will certainly bear them all in mind if I ever have another similar problem.
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Sounds like most fuel problems designed by poor builders when they seal sender units and tank hatches using too much sealant , it falls off into the tank. The last sealine sc29 I had the same problem with I found a half meter long piece inside the tank pick up pipe. Endless dealers miss diagnosed fuel related and turbo problems on this engine when in the end it was a simple installation issue and nothing more. Glad to hear you are at the bottom of this issue.
 
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