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Izuzu Engine - strange behaviour


WJM

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I had a strange experience with my Izuzu engine recently. On three occasions over two days it suddenly dropped revs. I was cruising along and suddenly the revs dropped and the engine seemed to be about to stop. I pushed the morse lever fully down, which would normally produce over 2000 rpm and the engine kept running at around 800 rpm. Then I pulled the lever to idle and the engine ran very slowly, much slower than normal idle but it never actually stopped. After a few minutes, on each occasion it recovered and carried on as normal.

 

Does anyone have any thoughts on what might have caused this? It has been running perfectly since these three odd occurrences. 

 

 

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2 minutes ago, WJM said:

I had a strange experience with my Izuzu engine recently. On three occasions over two days it suddenly dropped revs. I was cruising along and suddenly the revs dropped and the engine seemed to be about to stop. I pushed the morse lever fully down, which would normally produce over 2000 rpm and the engine kept running at around 800 rpm. Then I pulled the lever to idle and the engine ran very slowly, much slower than normal idle but it never actually stopped. After a few minutes, on each occasion it recovered and carried on as normal.

 

Does anyone have any thoughts on what might have caused this? It has been running perfectly since these three odd occurrences. 

 

 

I have had a couple of blocked filters and this sounds similar. Boat fuel tanks can be pretty awful inside with rust, water and slime inside and my first thought would be to change the filters then shine a torch into the tank to see what it looks like.

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OK - I have a fuel filter with a bolt on the bottom so I opened that and drained some liquid from it. I half expected some water but I got only water. 

I have run about 40 hours since the problem last occurred and it has been running perfectly. 

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If the prop is clear then it sounds fuelish or mechanical drag.

Was the slowing accompanied by clouds of black smoke? If not, drop and examine all the fuel filters. There may be ones in the lift pump and or fuel pump inlets as well asthe obvious.  Blow out the fuel feed back to the tank.  Examine a fuel sample taken from the bottom of the tank with a dip tube. 

Fit clean filters, bleed through and start.

 

N

 

Start with the dip tube sample above and get all the water out of the tank before doing the rest. Leaving water in the fuel system on the engine is a really bad idea.

N

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Thanks for the responses . things seem to be pointing to fuel supply.

 

The exhaust smoke remained clear through all of this.

 

It may be unrelated but... around the same time the Hours Counter (small LCD display in the centre of the RPM dial) began so display a scrambled display ie: just random lines, not proper numbers. There were many hours of this where the engine was running perfectly but this was the condition during the problem. The display has now corrected itself and is displaying normally again. 

 

Edited by WJM
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If the filter was full of water it was probably gobs of water getting through to the injectors. If you have a drain cock on the bottom of the tank, lean the boat over to the sides its on and drain some off. Also a small pump like a Pela pump with a thin probe tube poked down the filler and moved around the bottom of the tank to suck up any water. Check any seal on the tanks filler cap, a common cause for rain water entering the tank.

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It is essential to get rid of all the water and grot in the tank or you are likely to suffer from diesel bug.  It's also important to prevent water getting into the tank, for example through a deck filler.  The seal should be in good condition and the cap tightened down.  Even a poorly sited vent can allow water to enter a fuel tank.

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Water in the fuel can be a proper sod. I scrapped a large amount of diesel and water mix ( probably 30 - 40 gallons, and road diesel as well, not red) ) that I got from my fuel tank, it was so thoroughly mixed and sludged that I gave up any thought of salvaging it. After that the tank itself took a couple of days to clean as the access was so difficult through a small hatch. I really would try to get the contents out and get to grips with the problem. I suspect that the fuel additive I had used might not have helped either and caused the fuel / water to mix, when I read the label it seemed to say that small amounts of water in the fuel would mix and be consumed by the engine, maybe but large amounts from a leaky deck filler just made an awful mess.

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16 minutes ago, WJM said:

Thanks for the responses . things seem to be pointing to fuel supply.

 

The exhaust smoke remained clear through all of this.

 

It may be unrelated but... around the same time the Hours Counter (small LCD display in the centre of the RPM dial) began so display a scrambled display ie: just random lines, not proper numbers. There were many hours of this where the engine was running perfectly but this was the condition during the problem. The display has now corrected itself and is displaying normally again. 

 

That could tie up with the water in the tank. Rain!!  If the gauge is out in the weather unprotected from rain and damp. Half those VDO hour counters on boats don't work properly for that reason.

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23 minutes ago, WJM said:

Thanks for the responses . things seem to be pointing to fuel supply.

 

The exhaust smoke remained clear through all of this.

 

It may be unrelated but... around the same time the Hours Counter (small LCD display in the centre of the RPM dial) began so display a scrambled display ie: just random lines, not proper numbers. There were many hours of this where the engine was running perfectly but this was the condition during the problem. The display has now corrected itself and is displaying normally again. 

 

Fuel filters as others have said and then find source of water etc. The lcd reading is unrelated 99 percent of Isuzu displays fail.

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2 hours ago, WJM said:

OK - I have a fuel filter with a bolt on the bottom so I opened that and drained some liquid from it. I half expected some water but I got only water. 

I have run about 40 hours since the problem last occurred and it has been running perfectly. 

Apologies - I just noticed a typo - When I opened the fuel filter I got ONLY CLEAN FUEL - not water as I mistyped earlier. 

 

 

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4 hours ago, WJM said:

Apologies - I just noticed a typo - When I opened the fuel filter I got ONLY CLEAN FUEL - not water as I mistyped earlier. 

 

 

Sometimes the wholes inside the top of the filter get gunged up rather than water evident at the drain plug. I would change them all anyway and get a sample from the bottom of your tank to see if water is present. My boat has twin tanks both of which have built in drain taps to do the job easily but if not there are several methods such as a small electric pump or a pela pump to name but two ways of obtaining a sample.

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I was going to say "water in fuel", especially when you said, incorrectly, that you got water from the filter bowl.

However I think it is still a likely possibility; I have experienced something similar myself.

I would firstly check all the filters, but I would also check the bottom of the tank.  I do this using a piece of plastic tubing clipped to a wooden rod and then syphon out from the bottom of the tank.  With most tanks you can get a syphon going by holding the bottom of the tank near the bottom of the engine 'ole, i.e. below the bottom of the tank. Not possible of course if  you have an engine room with a baseplate tank.

In the case I mentioned above, the filter bowl has little water in it, but there was several litres of water in the bottom of the tank.  I suspect that because of some movement, the pickup dipped into the water, then went back to just above the fuel/water interface.

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Check the wiring connections to the electric fuel pump. I had something similar, the engine would start to stall, then the shuddering would move the wiring just enough to re establish connection. Took ages to trace. Although failing fuel pump is also a possibility.

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1 hour ago, mrsmelly said:

Sometimes the wholes inside the top of the filter get gunged up rather than water evident at the drain plug. I would change them all anyway and get a sample from the bottom of your tank to see if water is present. My boat has twin tanks both of which have built in drain taps to do the job easily but if not there are several methods such as a small electric pump or a pela pump to name but two ways of obtaining a sample.

My old Landrover use to get like that, no sign of any crud when you drained the bowl, but when you took the element out it was covered.

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Check the fuse in the loom near the starter solenoid, and any other connections including the multiplug in the loom. It sounds to me as if the power is being cut to the panel, and therefore the electric lift pump.

Some Isuzus will run all day with the lift pump off, other will start to run lumpy and stop very quickly.

A faulty starter switch can also have the same effect.

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I had almost exactly the same symptoms on our boat. It turned out to be swarf left in the tank when it was built being sucked into the fuel line. When the engine was stopped the flow through the fuel lines stopped and the engine would run fine again on start up, untill the next bit of swarf was sucked up.

 

Anth

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