Strange...

[pos]

Evening,

Some of you may know about the recent problems I've been having with my 2.5 N/A climbing hills at ridiculously slow speeds (i.e. 15mph in 2nd gear max). Well I've just been to drop a paper bag off at a house on a slope a couple of miles away and the thing pulled really well in second. I don't push my foot down, I keep my foot as high off the gas as possible but I really lifted my foot and the old gal shot off. The strange thing is, I didn't adjust my foot position for about 100 metres and the car kept jolting off and then retarding a little bit as if it was charging off and then slowing right down.

What could be causing this? Knackered lift pump? Dirty fuel filter?
I must mention that I had a fiddle with the manual pump whilst the engine was off.

I'm baffled
-Pos

 

[stig]

does sound like your lift pump is on its last legs, I have just replaced mine what a difference it has made.

 

[pos]

I always thought the lift pump was a manual pump unit used only when changing the fuel filter or a fuel pipe. What other purpose does it serve and how can it be affected by my throttle which is connected to the injector pump?

Thanks again
-Pos

 

[CharlesY]

Good grief ..... the lift pump LIFTS FUEL from the tank, FORCES it through the filter, and feeds it to the Injection pump. The injection pump contains its own little pump inside to deliver the fuel to the high pressure side, but this little pump CAN NOT SUCK. So diesel fuel MUST be sent at a nice gentle pressure to the injection pump, or you're stuffed for power, and that is what the lift pump or FUEL DELIVERY PUMP does - if it works properly.

Over and above that, I suspect it sounds like you have an air-leak INTO the fuel system, more than the filter head's fuel/air separation device can handle. It is almost inevitable this will be between the tank and the lift pump as the pipes and joints there are under VACUUM, not pressure, so any holes or leaks or slack joints lets air IN.

What does a replacement lift pump cost? Fifteen pounds?

Good investment ... If the old is knackered, bin it. If it isn't keep it for an emergency spare.

 

[pos]

Alright cheers, I'll have a good look in the morning to see if I can tighten up any of the hoses or find any thing blatently obvious!

 

[dirty hands]

fuel travels from the tank to the filter to the lift pump to the injector pump on mine. Is the lift pump electric or driven by something mechanical? In fact don't answer I'll have a look myself...

 

[discomania]

The strange thing is, I didn't adjust my foot position for about 100 metres and the car kept jolting off and then retarding a little bit as if it was charging off and then slowing right down.

How big were the jolts? The 2.5NA will do that slightly pulling up a hill slowly in second gear with not much throttle, its just the engine working at fairly slow speeds, if you gave it a little more gas it would work fine.

So it could just be that and its nothing to worry about, OR it is a fuel related issue, I think your getting excited about nothing.

Disconnect the output from the lift pump, and give it a few strokes, does fuel spill out? If not turn it over on the key a blimp (get the cam in the right position to let the lift pump work) then try again does it pump? If not replace it.

 

[dirty hands]

Now thats got me thinking. When I start mine it runs on diesel through the normal land rover fuel lines. Main Tank->Filter->lift->injection and then return to main tank. When the engines warm it will switch to veg oil and use the following...Aux tank->filter->injection pump and return to aux tank. I don't have a lift pump in the veg line. The aux tank is raised up in the back of the land rover and i thought gravity would be enough. Am I putting a strain on the injection pump? It runs very well on doth diesel and veg, can't tell the difference really.

What do you think?

Bye

 

[CharlesY]

Quote .....
fuel travels from the tank to the filter to the lift pump to the injector pump on mine. Is the lift pump electric or driven by something mechanical? In fact don't answer I'll have a look myself...

Are you sure about that?
It is more usual that the fuel goes from the tank to the lift pump then to the filter and then to the injection pump.

There are ALSO some extra pipes because there is one return pipe from the injection pump to the tank, another from one if the injectors to the tank, and probably one from the fule filter head to the tank.

These can all be arranged in various ways, usually combined at the filter head. but the supply side (which might be your problem) is usually arranged

TANK >>>> LIFT PUMP >>>> FUEL FILTER >>>>>>INJECTION PUMP

in that order.

 

[CharlesY]

On re-reading your message, you seem to make if plain that when running on veg oil there is NO LIFT PUMP involved.


I suggest you start thinking that this pump is better known as FUEL DELIVERY PUMP, because your injection pump needs fuel to be DELIVERED quite positively, or it simply doesn't get enough fuel and runs out of puff.

DIESEL TANK

OR >CHANGEOVER VALVE >LIFT PUMP > FILTER >INJECTION PUMP

VEGOIL TANK


The Injection pump cannot SUCK enough fuel to make the engine develop full power or anything like it.

I suggest a little re-plumbing is called for!

 

[dirty hands]

Quote .....
TANK >>>> LIFT PUMP >>>> FUEL FILTER >>>>>>INJECTION PUMP

in that order.

I've just looked. Your quite right , it does. My mistake. Gotta stop snorting wax oil....

 

[pos]

I'll go out and investigate. Something worth noting is that I don't have a seperate tank for veg oil. It's just mixed in with my Diesel but it seems to run well enough. I have got about a 65/35 mix, diesel being the stronger of the two.

Right, off I go...
-Pos

 

[pos]

How does the lift pump actually work then? There's nothing more than two fuel pipes, one in, one out and absolutely no wires as far as I can see

 

[dirty hands]

Thats what was bafflin me. I cant see how it's powered either.

I'm gonna read some stuff....

 

[stig]

the lift pump is operated by a lever that is in contact with an eccentric lobe on the camshaft, which is why sometimes on bleeding the fuel system you have to rotate the engine slightly to have the lever at the "bottom" of the lobe otherwise the external lever will not be able to operate.

 

[pos]

Oh rite thanks! I'm gonna have a better look around the thing. It just looked like a freestanding block to me but there's obviously an arm somewhere that I didn't see. It might be worth my while replacing it afterall

-Pos

 

[tom69]

just check this; i recently sold my 90n/a diesel lukily to a friend who said it spent about a week getting slower and slower until it just stoped. and every so often it would pull like a train for a few hundred feet. turn out it had stripped about 10 teeth of the timing belt. no enough to kill it but enough to bend a valve and remove its self from use for a weekend. i dont feel to bad, the cheque bounced.

 

[dirty hands]

Does that mean it pumps faster with the engine's rev's or does it remain constant...? all that 'eccentric lobe on the camshaft' stuff?

Cheerio

 

[CharlesY]

Don't worry about mixing the fuel from the return pipe with either of the others. Very little goes back, and it mixes beautifully anyway.

Unless your car goes noticeably BETTER on hills when running on veg oil or BioDiesel, then it is suffering some degree of fuel starvation.

I think you have been fairly lucky so far that it goes at all, so when you have revised the plumbing a trifle it should be great.

 

[CharlesY]

The lift pump is quite clever.
It pumps AS REQUIRED.

The thing PUMPS fuel by the pressure of a spring shoving a diaphragm, so no matter what, the pressure OUT of the pump cannot exceed a certain level as pushed by the spring.

The eccentric lobe on the camshaft only DRAWS THE DIAPHRAGM BACK, and in the process SUCKS fuel from the tank. So, as the SUCK is powered by the cam and lever, it is a powerful sucker, and can suck soft fuel pipes flat. So we use tough semi-rigid fuel pipes.

The fuel delivery / lift pump is always a DEMAND pump - so it only sucks IN and pumps OUT as much fuel as the engine uses, plus a tiny bit more that is leaked back from the injection pump, the 4 injectors, and (if fitted) the automatic air-bleed in the filter head.

The fuel pump operating lever does not run in full contact with the eccentric of the camshaft all the time. In normal running it only gets a little nudge each two turns of the engine, just enough to deliver the fuel needed, and no more.

Clever, huh?

Does that help?

CharlesY