Yanmar 4LHA-STZP engine troubleshooting question

salar

salar

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I'm tapping into the huge pool of knowledge on this forum! My relatively young engine has behaved very well until last weekend. After running for about 15 minutes at 3000rpm it suddenly lost power and stopped. I did all the usual checks, and tried to start again. After a lumpy couple of seconds it settled down. I ran it up to 2000 rpm and after about five minutes it lost power again. This time I caught it and nursed it home at 1500rpm. Back in the marina it had a thorough look over and nothing obvious came to light, no dirt in the fuel filters. Thinking it may have been gulping air in a low tank I filled right up and this weekend took her out again for a test run. Exactly the same happened. I had debris in the fuel tank once before on a different boat and that time the symptoms were different, it simply would not rev above a certain point. It still may be dirt in the tank, but can anyone with experience of these engines suggest anything else we could look into? Thanks in advance.
 
Air leaks in the feed pipes or filters or debris in pick up tube causing a decrease in fuel supply
these engines seem to suffer if there is the slightest problem in the fuel supply system
Just double check everything from tank to engine.

possibly even run a temporary supply line from tank to engine filter with a clear hose so you can look for air ingress from the pick up pipe
 
An old style diesel like this requires two things to run, fuel and air at the correct ratio so I'd say you have a fuel problem and by the sounds of it it's near the tank pick up pipe.
 
salar said:
Thanks, that confirms what I suspected, now to find the culprit...
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If it has the hand primer above the fuel filter on the engine , run up the engine at full throttle , watch it, if it falls down then it's a fuel blockage towards the tank, it won't fall if it's an air leak, they also fail and let air in so bypass it with a piece of pipe for a short while.
 
I have removed the dip pipe and sucked 20 litres of fuel out of the bottom of the tank by the pickup with a high speed pump. There is no evidence of any blockage and no debris of any kind seen. We can't replicate the problem at the berth so I took the boat out for a run in the harbour. It was an exact repeat of the problem: after running for about ten minutes at 2000rpm then after about three minutes at 2500rpm the engine started stuttering. This time I couldn't catch it, it just died. Nervous moment. I restarted OK and crept home below 2000rpm. Volvopaul - the manual fuel pump is by the fuel pump which is below the fuel filter, will this type behave in the same way? Now for some serious air leak detection. Any likely trouble-spots to look for?
 
I would say don't look for an air leak, look for a blockage. When there is a blockage the lift pump sucks like mad and creates a vacuum in the pipe, a joint that ordinarily would be fine starts to let air in.

Hence a blockage manifests itself as an airleak.
 
If you have a clear fuel filter you may see air bubbles being pulled through, in which case tighten up joints.

Alternatively you sometimes get swarf or debris obstructing the pickup line, disconnect at the fuel filter and blow back with an air line or dinghy pump, then re prime fuel and run up and see if any difference.
 
You do not mention it but is this engine turbo'd and intercooled? also any black smoke as the power drops off, if so then clean out the charge air can. Remove the end caps then remove the matrix, if it is anything like my mates 6 cylinder job it will be full of muck.
 
Good suggestions, thank you. I assume air leaks can only occur before the pump, i.e. when the fuel is being sucked, not afterwards where it is under pressure, or am I wrong? Some of the hoses on top of the filter look a bit dated, although the feed from the pump and the return to the tank look ok. I'm not sure what the others do! I also heard somewhere that the inside of hoses can delaminate and create a blockage, is this true?
 
omega2 said:
You do not mention it but is this engine turbo'd and intercooled? also any black smoke as the power drops off, if so then clean out the charge air can. Remove the end caps then remove the matrix, if it is anything like my mates 6 cylinder job it will be full of muck.
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Yes to both. I'll try that too (when I can find it) - thanks.
 
omega2 said:
You do not mention it but is this engine turbo'd and intercooled? also any black smoke as the power drops off, if so then clean out the charge air can. Remove the end caps then remove the matrix, if it is anything like my mates 6 cylinder job it will be full of muck.
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4 cylinder turbo charged with intercooler.

I had the STP version on our last boat which came with this primary filter http://separfilter.com/fuel-water-separators/swk-2000-5-50-single-clear-bowl-copy

It was awkwardly placed and not easy because of the four screws to seat the top plate after a filter change accurately without a poor seal. I had occasions when it łet air in causing issues so changed for a Racor FG500 on the basis I did not want this issue if the need arose to change filters at sea.

may be nothing to do with your issue but it took a while to track down my issue.
 
On the six cylinder job, the air cleaner (a circle of black foam rubber) on the intake side of the turbo was clogged, but worse still is the method of crankcase breathing, i.e. a pipe coming off the rocker cover straight into the air intake, so the engine is breathing it's own ****.
 
There are two bolts holding the starter to the motor. They are on opposite sides from one another.
Depending on accessibility to the motor, doing the starter can be very difficult or a breeze. It depends on if you can get down to the rear lower side of the block back by the flywheel. If you can, it is a simple matter of disconnecting the battery cable and a couple wires, the two bolts and done.
 
mtb said:
time for a new lift pump
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You might be right there. The engineers have checked the hoses with a vacuum gauge and all looks fine. Next step is to run the engine from an independent fuel tank to finally prove it is not something in the tank, although I cant see how a lift pipe with two side holes and an end hole can get blocked by a lump of something and there isn't any loose debris in there.
 
salar said:
You might be right there. The engineers have checked the hoses with a vacuum gauge and all looks fine. Next step is to run the engine from an independent fuel tank to finally prove it is not something in the tank, although I cant see how a lift pipe with two side holes and an end hole can get blocked by a lump of something and there isn't any loose debris in there.
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it could be as simple as one of the non return valves in the lift pump sticking with the gauge connected the pump should show between 1.3/4 to 2.1/4lb pressure ish, but a sticking valve might not present its self at the time of checking
Is the fuel tank vent clear ? have you tried seeing if a vacuum is building up in the tank
Mind you an electrical fault could cause it re the wirering to the stop solenoid or fuel cut off valve in the pump, intermittent faults can be hard to pin down its only checking it over with the fault present that you might find out whats causing it
If it was an air leak starting from cold would be a problem this was not indicated per the post
 
your right to a point but whose to say if you've had a mechanic check it then it wont be / might not be obviouse
if it starts ok after being left then rule out air leaks as you'd find it has to self bleed before starting, this could also be the case if fuel is not getting to the engine due to a vaccuum
If after you run the engine it stops then after a while you can re start it check the tank vent I'd even try leaving the fuel filler off if possible to rule out a vaccuum build up in the tank, re this as soon as it stops undo the fuel filler if it sucks then you might find your fault is a simple blocked vent
electrics
check the electrical connections and also the stop solenoid if the solenoid has gone out of ajustment it may cut out due to vibration the same with any of the connections
with the engine running check each connection on the engine also all the main loom connections
a simple wiggle of the wire will soon stop the engine if its the actual fault
 
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