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martynw
martynw

Posted: Sun Sep 01, 2019 3:36pm

Post Subject: Isuzu engine problem

I have an Isuzu 42 engine with less than 500 hours use. Very recently it has begun to cause problems. It starts absolutely fine but after a few minutes, it begins to “hunt” and then stalls. If you leave it for 15 to 20 minutes it will start and run perfectly normally. I have had an engineer to look at it and the fuel was flowing freely. Both it and the filter were clean and there were no obvious problems. The fuel pump appeared to be working correctly. In the end he thought it might be a very slightly loose crimp connection to the fuel pump and so this was replaced and the engine appeared to be back to normal. A week later the same problem has arisen. I can only assume that there must be a fault of some kind with the fuel pump but would welcome suggestions/advice before calling out another engineer. Many thanks, Martyn

Tony-B
Tony-B

Posted: Sun Sep 01, 2019 3:57pm

Post Subject: Isuzu engine problem

Some Isuzus have a mechanical fuel pump and some an electric one so the first thing to check if you have an electric pump is that its connections are clean and tight and also that any large multi-pin connectors in the main engine wiring harness are clean, dry and tight. Next try running it with the filler cap off. These are the classic symptoms of a bocked fuel tank breather. Drawing fuel from the tank gradually causes a vacuum in tank stopping the fuel flow. Then when left air manages find a way into the tank slowly so it will start and then the whole sequence starts again. I very much doubt its an injector pump problem because you have four of them and if one stopped working the other three would keep the engine running but roughly. It might be a lift pump problem but narrowboat fuel tank fuel levels are usually higher than the engine so it will gravity feed to a degree. This does not rule a faulty lift pump out but makes in unlikely. As both the fuel and filters were clean I very much doubt you have a fuel contamination problem and or that muck has caused problems in the lift pump. If the fuel return to the tank is blocked it could allow air to build up in the system and stop the engine but then it would still be there after teh 20 minutes.

martynw
martynw

Posted: Sun Sep 01, 2019 5:31pm

Post Subject: Isuzu engine problem

Thank you for your suggestions. Both I and the engineer checked the wiring connections and all seemed fine, but will check again. Your suggestion about a blocked breather pipe is interesting, but I don’t understand how when it does eventually start that it will run for hours without a problem and then the next day it all starts over again. Martyn

Tony-B
Tony-B

Posted: Sun Sep 01, 2019 6:25pm

Post Subject: Isuzu engine problem

I have no idea how old the engine is or how many hours it has done but if either are considerable and you have an electric lift pump then the contacts inside it could be burned/worn. Try rigging a temporary gravity fuel feed or fit a temporary Facit type electric fuel pump.

martynw
martynw

Posted: Sun Sep 01, 2019 8:12pm

Post Subject: Isuzu engine problem

The engine is 10 years old but has less than 500 hours of use. It has an electric fuel pump which you can feel pulsating rapidly, so I assume it is working. There is absolutely no problem with the fuel flowing to the fuel filter. Martyn

Tony-B
Tony-B

Posted: Sun Sep 01, 2019 8:59pm

Post Subject: Isuzu engine problem

It is not unknown for electric fuel pumps to become very erratic, sometimes running for days or weeks before stopping then vibration or a knock would allow it to start again and run for more time. However this is very far from definite and is why I suggested rigging a gravity fuel tank or fitting another electric to see if it stops the problem. There might be something floating about in the tank that floats to the intake and blocks the pipe but as you say the filter is clean its not so likely. Sometimes the dip pipe in the tank splits or perforates so in effect it runs out of fuel with lots in the tank but that does not accord with the symptoms you gave me. I can't think of anything else that will help you.

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