Izuzu Engine - Strange running

[WJM]

I am having an ongoing problem with my Izuzu engine:

 

Engine starts normally and runs well, sometimes for hours. Then suddenly for no reason the revs drop right down. So I push the throttle fully forward and the engine continues to run but only at very low revs. It continues to run like this for a long time, enough to get me to a safe mooring. It never actually stops but the revs rise and fall with no pattern. There is no smoke from the exhaust although the exhaust note sounds different. The engine is not consuming oil or water any more than it usually does. The fuel-line water-trap is totally free of water. I moor up, stop the engine and wait a few minutes and it fires up and runs normally again.

 

Something that may or may not be relevant - the Aux light on the control panel lights up continuously when the engine is running. This may or may not be normal, I have no idea. Something tells me the problem may be electrical. But I am definitely no expert!

 

If anyone has any thoughts on what might be causing this I would be pleased to hear them!

[Stilllearning]

Two immediate thoughts occur to me: 

1  the aux light may have something to do with battery charging, can you check the voltage at the batteries with the engine running.

2  the engine will have an in-line fuel pump either an electric or mechanical one running off the engine, have you looked at the filter that will be inside it.

 

[Alan de Enfield]

Assuming your oil pressure gauge is working correctly have you checked the oil level in the sump ?

 

The reading looks to be considerably higher than it should - I cannot imagine any installer using a gauge that is pegged at the top of its range at 'normal' pressures, otherwise how would you know when its too high ?

[WJM]

1 minute ago, Alan de Enfield said:

Assuming your oil pressure gauge is working correctly have you checked the oil level in the sump ?

 

The reading looks to be considerably higher than it should - I cannot imagine any installer using a gauge that is pegged at the top of its range at 'normal' pressures, otherwise how would you know when its too high ?

The oil pressure gauge has aways read like that - for twelve years now. I agree with what you say though. But I don't think oil pressure would cause this problem.

[Chewbacka]

8 minutes ago, WJM said:

The oil pressure gauge has aways read like that - for twelve years now. I agree with what you say though. But I don't think oil pressure would cause this problem.

As it's been like it for 12 years I guess it does not bother you.  But if you would like it to work, something to think about - Pressure gauges go full scale when the sender signal is no good.  So you probably have a good +12v and negative (earth on a car) to the gauge head, but the sender is not giving the correct 'signal'.  It could be that the sender wire is either disconnected or broken or poor connection or the sender itself is duff.

 

 

[Onewheeler]

Blocked vent causing partial vacuum in the fuel system maybe? Doesn't sound like an electrical problem.

[mrsmelly]

4 hours ago, WJM said:

I am having an ongoing problem with my Izuzu engine:

 

Engine starts normally and runs well, sometimes for hours. Then suddenly for no reason the revs drop right down. So I push the throttle fully forward and the engine continues to run but only at very low revs. It continues to run like this for a long time, enough to get me to a safe mooring. It never actually stops but the revs rise and fall with no pattern. There is no smoke from the exhaust although the exhaust note sounds different. The engine is not consuming oil or water any more than it usually does. The fuel-line water-trap is totally free of water. I moor up, stop the engine and wait a few minutes and it fires up and runs normally again.

 

Something that may or may not be relevant - the Aux light on the control panel lights up continuously when the engine is running. This may or may not be normal, I have no idea. Something tells me the problem may be electrical. But I am definitely no expert!

 

If anyone has any thoughts on what might be causing this I would be pleased to hear them!

Try changing the spin off fuel filter that is screwed upside down in to the shiny housing just in front of the oil extraction hand pump.

The aux light is showing a fault on domestic battery bank charging.This works independant of the water pump that one shows charge on the voltage gauge for the engine start battery.

Many Isuzu set ups read high on the oil pressure gauge and I expect your hours gauge is about to pack up soon as most of them do.

Your engine temperature is spot on.

Edited May 4, 2018 by mrsmelly

[Boater Sam]

Blocked outside fuel tank vent, the gauze gets blocked especially if you Brasso it.

If its an electric fuel pump it will have a small filter in it behind the cap at the end. If mechanical it could have a gauze under the top if its detachable.

Air getting into the fuel line before the injection or lift pump.

Rubbish slopping around in the fuel tank blocking the pickup pipe.

If the engine runs badly without smoke, it is being starved of fuel one way or another.

 

 

[Flyboy]

Sounds like fuel starvation to me. I'm pretty certain the Isuzu has a Chinese electric fuel pump.  I'd start looking at this by taking off the outlet pipe, put it in a container (jam jar) and switching on the ignition. the pump will click as it pumps.  Also I would replace the fuel filters as a matter of course. If the pump is faulty I would recommend you fit a Facet Posiflow pump. (about £35)

[WotEver]

1 hour ago, Flyboy said:

Sounds like fuel starvation to me. 

Me too. In order of likelihood imho...

 

1. Fuel filter blocked, especially if it’s one of those tiny bayonet fitted ones on the fuel pump. 

 

2. Crud in the tank blocking the outlet. 

 

3. Faulty pump. 

[mrsmelly]

9 hours ago, WotEver said:

Me too. In order of likelihood imho...

 

1. Fuel filter blocked, especially if it’s one of those tiny bayonet fitted ones on the fuel pump. 

 

2. Crud in the tank blocking the outlet. 

 

3. Faulty pump. 

As I suggested replacing the spin off filter the size of an   oil filter which the op didnt mention,  1 minute job and self bleeds via lectric pump so a complete doddle.

[MtB]

Sounds like no air getting into the diesel tank to me, to replace diesel used. The longer the engine runs the harder the fuel pump has to suck. If it was a blocked fuel filter I’d expect the problem to surface quickly, not take several hours of running. 

[dccruiser]

3 hours ago, Mike the Boilerman said:

Sounds like no air getting into the diesel tank to me, to replace diesel used. The longer the engine runs the harder the fuel pump has to suck. If it was a blocked fuel filter I’d expect the problem to surface quickly, not take several hours of running. 

I agree its a strong possibility ... if it happens i would take the fuel filler cap off ... you will probably hear it suck as you release the pressure .... and it should then run as normal, easy check just to rule it out.

Rick 

[Detling]

You have a dirty great multi plug and socket in the electrical harness between the engine and the instrument panel. These cause no end of interesting faults, sounds like yours is cutting off the fuel pump and the alternator exciter wire. Mine often cuts the stop button as well. You need to open the connector and clean the contacts, coat in suitable waterproof grease, gently squeeze or bend the connector bits so they make good contact and you should have no more trouble for a few days even weeks. They can go for years I have been told but in my experience I have never gone for more than 18 months. I keep saying I will replace it with something better but never done it.

Problems it can cause

      Glow plugs not working

      Rev counter not working or jumping all over the place.

      Turning the key does nothing (same as a blown fuse)

       Stop button does nothing

       Alternator light flickers doesn't go out or come on

       Spluttering running slows down speeds up on it's own

That's all I can remember for now, it is the first thing I wiggle and frequently the answer.

[MtB]

57 minutes ago, Detling said:

You have a dirty great multi plug and socket in the electrical harness between the engine and the instrument panel. These cause no end of interesting faults, sounds like yours is cutting off the fuel pump and the alternator exciter wire. Mine often cuts the stop button as well. You need to open the connector and clean the contacts, coat in suitable waterproof grease, gently squeeze or bend the connector bits so they make good contact and you should have no more trouble for a few days even weeks. They can go for years I have been told but in my experience I have never gone for more than 18 months. I keep saying I will replace it with something better but never done it.

Problems it can cause

      Glow plugs not working

      Rev counter not working or jumping all over the place.

      Turning the key does nothing (same as a blown fuse)

       Stop button does nothing

       Alternator light flickers doesn't go out or come on

       Spluttering running slows down speeds up on it's own

That's all I can remember for now, it is the first thing I wiggle and frequently the answer.

 

None of this quite explains why the engine runs fine for several hours before the fault presents itself. 

[Tony Brooks]

Vibration and expansion due to heat but although it needs checking I also suspect the tank breather or muck floating in the tank.

[WJM]

Thank you for all the inputs on this topic. 

 

A detail I omitted earlier - when the problem first occurred I opened the fuel filler cap in case a partial vacuum was causing fuel starvation. There was no noticeable pressure difference and the engine continued to struggle.

 

I have decided to have the fuel pump replaced. This in itself may solve the problem or possibly the whole process of fitting a new pump may flush out the problem.

 

 

[ditchcrawler]

7 minutes ago, WJM said:

 

I have decided to have the fuel pump replaced. This in itself may solve the problem or possibly the whole process of fitting a new pump may flush out the problem.

 

 

What has made you come to that decision?

[WJM]

39 minutes ago, ditchcrawler said:

What has made you come to that decision?

An overview of all the pointers offered here. It is a low cost simple approach that covers the majority of the suggested causes. 

Edited May 9, 2018 by WJM

[WotEver]

28 minutes ago, WJM said:

An overview of all the pointers offered here. It is a slow cost simple approach that covers the majority of the suggested causes. 

It’s an expensive way of replacing a little filter...

[WJM]

3 minutes ago, WotEver said:

It’s an expensive way of replacing a little filter...

Peace of mind has no price!

[WotEver]

1 minute ago, WJM said:

Peace of mind has no price!

Do you also replace your car when it needs an oil change?

[WJM]

4 minutes ago, WotEver said:

Do you also replace your car when it needs an oil change?

Each to their own. Thanks for your input.

[cuthound]

49 minutes ago, WotEver said:

Do you also replace your car when it needs an oil change?

 

No, he doesn't wait that long, he changes is when the ashtray is full ?

Edited May 9, 2018 by cuthound
To add a missing worm

[WotEver]

6 minutes ago, cuthound said:

 

No, he doesn't wait that long, he changes is when the ashtray is full ?

I was gonna write that but expected “I don’t smoke” as a response