Posted: Wed May 06, 2020 10:33pm

Hello, I have a Isuzu 4LC38 engine. I have had a problem with diesel bug which has been sorted out. Now when I try to start the engine it takes lots of cranking to start with lots of white/grey smoke. All the filters and fuel lines have been replaced. I have checked the heater plugs. When you undo the bolt on injector no 4 the engine starts straight away. When you tighten it up again. The engine runs fine but there is a slight hunt at idle. Do I need to have injector no 4 repaired? Or is there anything that could be wrong with the engine. Thanks for you time James.

Posted: Thu May 07, 2020 9:16am

This sounds to me like air in the fuel system. If it were an injector [problem which is unlikely anyway) you would be complaining about smoke when running, rough running and/or a proper misfire. As giving any air an "easy way out" by opening an injector pipe seems to allow it to start it suggests there is an air leak into the system and its so bad it is too much for the self bleeding capabilities of the engine. I suspect air gets in when its stationary. Do you really mean that you have had all the metal fuel pipes replaced. If so i would suspect a loose joint somewhere. Some Isuzus have an electric fuel lift pump and some mechanical but on a narrowboat typical tank heights means they will gravity feed to a degree so make sure if you have an electric lift pump a wire has not fallen off during the bug eradication work. I very much doubt its an injector fault, they are very simple devices.

Posted: Thu May 07, 2020 9:20am

A further thought. If you have any two or three part water traps/filters between the tank and lift pump make sure the sealing rings between the parts are properly located and not twisted.

Posted: Thu May 07, 2020 12:05pm

Hello thank you very much for your reply. I have replaced all the rubber fuel lines. The boat has a fuel guard filter with the kit for self polishing fuel. I can see no leaks in the fuel lines. The engine has a electric fuel pump. All the wires are on. Thanks for your time James.

Posted: Thu May 07, 2020 3:01pm

It is rarer for an air leak into the system to show as a fuel leak so having no visible fuel leaks proves nothing I am afraid. How are the flexible hoses clamped onto the pipes or end fittings. If Jubilee clips are used are they the correct size. If they are too large they may appear to clamp up but there will be two points either side of the screw that do not clamp properly. Occasionally a swaged clamp does not make an airtight seal. Are you sure the fittings in the new fuel guard are properly fitted/sealed. I think the unit also has an O ring to seal the bowl to the head. Silly thought - do you have at least 6" of fuel in the tank? The pickup is often 4" or more above the base of the tank.

Posted: Thu May 07, 2020 4:35pm

The fuel tank is full. All the fuel lines are clamped with jubilee clips. Could the air leak be in the fuel return pipe. The only thing that I have done from the engine working and not is clean out the fuel guard but all the seals seem ok none are bent or broken. I have changed the primary engine filter but not with a genuine isuzu filter. I have also fitted a new fuel isolator tap and I have re routed a fuel return pipe. Could any of these be a problem? Thanks James.

Posted: Thu May 07, 2020 4:57pm

As long as the pattern fuel filter is not a fake and is from a reputable supplier it is unlikely to be the problem as long as you lubricated the seal before fitting. So how long are the "tails" on the Jubilee clips (the bit that comes out of the clip as you tighten it). Up to maybe half an inch its probably OK but if its more the clip is probably too large for the hose. If the return pipe is kinked/flattened or is blocked then that would compromise the self bleeding. Anything could/might be the problem including the new fuel tap if it allows air find is way into the system, this includes the fuel guard seals and all the pipe unions. Have you tested the volume of fuel delivered from the lift pump. I have known the valves in lift pumps to be clogged by bug and/or dirt.

Posted: Thu May 07, 2020 5:26pm

There is lots of fuel coming from the fuel pump. I could try putting the fuel return pipe into a jug to see if there is a blockage in the pipe in the tank. All the jubelee clips have a very short tails. I can try re sealing the fuel tap because it's inline in the hose. Thanks James.

Posted: Thu May 07, 2020 5:36pm

Have you just pushed the hose over the pipes or have you fitted a proper barbed end to the pipe and pushed the hose over that. I am not sure how you can fit a tap into a run of hose unless you screw some form of hose barb into the tap threads. Yes it would be worth checking the flow in the return pipe. engine stopped, ignition on.

Posted: Thu May 07, 2020 6:35pm

The shut off tap has hose tail ends on the tap. There is fuel flowing down the return pipe. When the fuel pump is off and a lot more fuel when the pump is on. It feels like there is a small amount of diesel around the shut off tap.

Posted: Thu May 07, 2020 7:44pm

What type of tap? Is is a ball valve or a taper plug type. If the former and its leaking but not from the connections I fear its a faulty tap. If its the latter try turning it on and then using a smallish hammer driving the taper into its housing. This may make it more difficult to use but it may well seal better.

Posted: Thu May 07, 2020 8:11pm

I have attached a picture of the tap it has a stainless steel ball valve. The pipe fittings thread into the tap body. The thread looks tapered.

Posted: Thu May 07, 2020 8:22pm

That is a ball type valve. The spindle should be sealed with a small O ring. Did you fit the hose tails and if so what did you use to seal the threads. I would suggest washing the tap and close by pipes in something that will remove any diesel. Then carefully dry and dust with talcum powder and leave alone for a while. any darker talcum dust will show where the leak is. Incidently in my experience yellow tap parts usually indicates gas and that means a gas cap tap is primarily deigned to work with pressure and not a potential suction

Posted: Thu May 07, 2020 8:37pm

I originally sealed with ptfe tape but one side of the tap was leaking badly so I sealed with loctite 577. The other side is still sealed with ptfe tape.

Posted: Thu May 07, 2020 8:49pm

As long as you took care no to put the Locktite on the innermost couple of threads that side should be fine. I am not so sure about the PTFE tape, especially if you did not take exceptional care not to wind it onto the innermost threads. I would be concerned about scraps getting into the fuel system, however the Fuelguard and the engine filter should catch such scraps. Try turning the ignition on a few minutes before trying to start the engine. If it starts more easily it would tend to confirm its air in the fuel.

Posted: Thu May 07, 2020 8:55pm

OK thank you very much for your assistance. I will try to find the air leak and re seal the shut of tap. Thanks again James