Fuel Pump

[WJM]

I have questions regarding fuel pumps generally. I am asking so that I can better understand a problem that I had with my Isuzu engine. 

 

If the fuel pump is is not working at all will the engine still run, albeit run badly or intermittently?  And building on that question - if the ignition key is accidentally knocked to the off position  would that have the same effect as a failed fuel pump - ie: the engine will still run, but badly because there is no electrical power going to the fuel pump?

[Boater Sam]

All depends on whether the engine can get enough fuel by gravity which depends on physical layout and tank levels.

 

You ask - Why? Do you have a fuel problem? Check all the fuel filters including the one in the pump.

[Horace42]

24 minutes ago, WJM said:

I have questions regarding fuel pumps generally. I am asking so that I can better understand a problem that I had with my Isuzu engine. 

 

If the fuel pump is is not working at all will the engine still run, albeit run badly or intermittently?  And building on that question - if the ignition key is accidentally knocked to the off position  would that have the same effect as a failed fuel pump - ie: the engine will still run, but badly because there is no electrical power going to the fuel pump?

As Boater Sam says, the pump is to get the fuel to the engine....and once running the engine will keep going until the fuel supply valve (mechanical or electrical) on the injector pump is shut.... or worse if the fuel tank empties - the engine sucks in air and stops.  You will then have to go through a messy procedure to 'bleed' the air from the injector pump to get the engine to start again.

 

[BEngo]

What sort of fuel pumps are we talking about?.  There are lift pumps, which supply fuel from the tank to the engine and injection pumps which take the fuel from the lift pump and provide the high pressure  at the exact timing necessary for the engine to fire.  Not all engine installations need a lift pump,- if the fuel tank/level is high enough the fuel will get to the injection pump by gravity.

 

N

[Boater Sam]

From your reference to ignition switch I assume you are talking about an electric fuel lift pump. They have a filter in the bayonet end cap.

 

Edited March 5, 2019 by Boater Sam
duplicated

[WJM]

Thank you for the responses - which generally go far beyond answering my original question.

 

So to be clear, the consensus here is that an engine fuel pump that is disabled (through a fault or through a loss of electric power) will not immediately and definitively cause the engine to stop? The engine can keep running, the fuel can still make it's way through to the injectors? Or to phrase it differently - a dead pump does not necessarily mean a dead engine?

 

 

 

 

[Horace42]

34 minutes ago, WJM said:

Thank you for the responses - which generally go far beyond answering my original question.

 

So to be clear, the consensus here is that an engine fuel pump that is disabled (through a fault or through a loss of electric power) will not immediately and definitively cause the engine to stop? The engine can keep running, the fuel can still make it's way through to the injectors? Or to phrase it differently - a dead pump does not necessarily mean a dead engine?

Can't answer with a definite yes or no. The engine needs fuel and will run without a pump if the fuel can reach the engine without a pump... in which case the engine will run when the pump fails

If a pump is needed to get fuel to the engine, then at some point in the operation cycle the engine will stop if the pump is fails.

[Detling]

mine goes into lumpy mode after about 20  seconds and goes back to normal when you put the key in the right place. I have never had it actually stop but it has only been in lumpy mode twice first time perhaps for two minutes before we worked it out, second time we spotted it straight away.  I blame my son by the way.

[WJM]

It is a very standard narrowboat layout. The rear end of the hull is partitioned off to form a diesel tank, the engine is mounted conventionally beside it. The pump is a small and simple looking device mounted on the side of the engine just downstream of the fuel filter so it must be a lift pump. I had an intermittent problem where the engine would run very irregularly for brief periods and then recover and run normally.

 

After much messing about with filters and other ideas which did nothing to solve the problem, I eventually replaced the pump and the problem disappeared. But it occurs to me now that the problem was identical to what is experienced when the ignition key has been accidentally knocked to off, the engine runs but struggles intermittently. The knocked key is easy to spot - all the instrument dials flop to zero so presumably all the electrics are unpowered - including the lift pump.

 

I generally tend to travel with my diesel tank very full and I carry a set of full jerrycans too. Every time I had this problem of the engine starting to struggle one of the many things I did to recover was to fill the diesel tank back up to full. On reflection, I think the lift pump must have totally failed but as long as the tank was full the pump was not needed. Only when the level in the tank fell to a point about level with the pump did the problem occur. The engine ran at idle but could not accelerate. 

 

I am just trying to get my head around what actually happened. And this thread might help others - a temporary fix for a failed lift pump may be to keep the tank full?

[Jen-in-Wellies]

Worth checking any engine wiring plugs and sockets. These are notorious for bad electrical connections, or just coming apart while underway. If your boat has an electrical lift pump, then a bad connection here could be a cause. My boat has a mechanical lift pump and on the couple of occasions that the engine wiring plug and socket have come adrift the engine just carries on running. The electrical stop solonoid won't work, so you have to know exactly where to poke it to stop the engine.

 

Jen

[RLWP]

Do Isuzu engines have an electric fuel pump?

 

Richard

[WJM]

My  Isuzu has an electric pump. 

 

The fault has been fixed - and has been for some months now. But since it developed I had stopped going out on the tidal Thames. On my last run up to Teddington it did it's frightening thing and I have not been out there since. But I have had months of reliable canal running now so I am getting ready to go back out. But I wanted to fully understand what I was dealing with in case anything flared again.

 

I have now added an extra tideway safety check to my list. A full fuel tank provides safety cover for a failed fuel pump. It seems that on my boat, the fuel pump is only required when the tank level falls below the level of the pump. 

[Tony Brooks]

15 minutes ago, RLWP said:

Do Isuzu engines have an electric fuel pump?

 

Richard

A I understand it some do and some don't and I don't think it is like the "Vetus" style pump Sam is talking about with the filter in the end.

 

I would expect a typical narrowboat with a full tank to gravity feed enough to keep the engine running without a  working lift pump but probably with reduced power and performance.

[RLWP]

6 minutes ago, Tony Brooks said:

I would expect a typical narrowboat with a full tank to gravity feed enough to keep the engine running without a  working lift pump but probably with reduced power and performance.

 

There are plenty of SR engines in canal boats with no lift pump at all

 

Richard

[Mike55]

Presumably out on the tideway you're running at higher revs than on a canal, so using more fuel so the limitations on fuel flow rate due to relying on a gravity feed will be more likely to restrict engine performance/running.

[RLWP]

2 minutes ago, Mike55 said:

Presumably out on the tideway you're running at higher revs than on a canal, so using more fuel so the limitations on fuel flow rate due to relying on a gravity feed will be more likely to restrict engine performance/running.

I doubt it. Say 2 litres an hour, 33 mil a minute. It's not much of a flow rate

 

Richard

[Chewbacka]

My engine (beta 43) is just gravity fed, no electric lift pump.  Going against the flow on the river Severn I reckon to use more like 5 or 6 litres per hour, but that is still not a lot of ml per min.

[ditchcrawler]

If an electric lift pump fails then surly parts of the fuel system that are normally pressurized will now be under vacuum so the slightest leak could allow a small amount of air in even if the injector pump can drag the fuel from the tank. Thinking about it when the electric pump is running any air drawn into the system between the tank and the pump would be discharged through the filter vents under pressure.

 

[RLWP]

7 minutes ago, ditchcrawler said:

If an electric lift pump fails then surly parts of the fuel system that are normally pressurized will now be under vacuum

 

 

Not necessarily. It depends how much head of fuel there is and how much resistance to flow through the pump. For a diaphragm pump wit flap valves, I doubt you'd get below atmospheric pressure

 

You could make a similar argument about the fuel pump 'sucking' fuel from the tank

 

Richard

[Mike Adams]

On my Isuzu55 as soon as you turn the ignition switch on the electric pump starts running and pumps fuel back into the tank. You can hear it running in when the tank is near empty. As the tank is above the level of the injection pumps it makes no difference if you turn the ignition and pump off, the engine just keeps running. It is good to know it will still run if the electric pump packs up - probably the most unreliable thing on the engine.

[ditchcrawler]

56 minutes ago, RLWP said:

 

Not necessarily. It depends how much head of fuel there is and how much resistance to flow through the pump. For a diaphragm pump wit flap valves, I doubt you'd get below atmospheric pressure

 

You could make a similar argument about the fuel pump 'sucking' fuel from the tank

 

Richard

I did and said any small amount of air would be pushed out through the bleeds in the filter heads

[RLWP]

1 minute ago, ditchcrawler said:

I did and said any small amount of air would be pushed out through the bleeds in the filter heads

Which side of the pump is the filter?

[BruceinSanity]

1 hour ago, Chewbacka said:

My engine (beta 43) is just gravity fed, no electric lift pump.  Going against the flow on the river Severn I reckon to use more like 5 or 6 litres per hour, but that is still not a lot of ml per min.

Come to think of it, so is mine. Not on the boat at the mo to check exact heights, but presumably as long as the injector pump is more or less at or below the level of the uxter plate, once you’ve got fuel through to it, it will continue to syphon up out of the tank and down to the engine.

[Tacet]

16 hours ago, Chewbacka said:

My engine (beta 43) is just gravity fed, no electric lift pump.  Going against the flow on the river Severn I reckon to use more like 5 or 6 litres per hour, but that is still not a lot of ml per min.

Yes.

 

And if you're running with the tide (as is conventional) up to Teddington, you don't need any more power beyond that required to make good steering.  If you go any faster, you shoot through central London so fast there is no time to enjoy the sights.