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Fuel lift pump


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To the best of my understanding - and I'm happy to be corrected here, the main (injector) fuel pump is designed to deliver fuel at a high pressure and precise timings to the injectors, but is not designed to suck fuel from the tank, so the lift pump has the job of getting fuel from the tank to supply the injector pump.

If the lift pump is "dodgy", I would suggest starting or running at any speed where the fuel demand is higher may be a problem.

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the lift pump gets the fuel from the tank to filter/FIP, the FIP is a very higher pressure unit & not designed to lift fuel from the tank, it's there to feed the injectors at high pressure, a 200tdi FIP rworks at around 280 atmospheres aka [bar]

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You definatly know when your lift pump is on its way out - amongst many symptoms some are, doesn't rev, lots of black smoke, uneven iddleing, engine "hunting"...

I belive its as crwoody described.

I also have a smoking problem and am working my way through the possibilities.... but, how does a failing lift pump lead to lots of black smoke? I thought that black smoke was caused by incompletely burnt fuel/excessive fuel, but a failing lift pump should give you less fuel shouldn't it? I am not doubting the statement. My understanding of what's going on is clearly over-simplistic!

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I also have a smoking problem and am working my way through the possibilities.... but, how does a failing lift pump lead to lots of black smoke? I thought that black smoke was caused by incompletely burnt fuel/excessive fuel, but a failing lift pump should give you less fuel shouldn't it? I am not doubting the statement. My understanding of what's going on is clearly over-simplistic!

Black smoke, blue smoke, white smoke... if your lift pump is failing it can cause intermittend fuel flow that can draw air into the system and it messes up the whole combustion process, but yes, black smoke is usually associated with overfuelling of one sort or another (faulty injectors/injector pump), blue smoke is burnt oil and white is steam implying water in the system.

If you have a lift pump problem you will find the engine will not run smoothly (even rev's) as the lift pump is purely mechanical its speed is adjusted with the engine speed, if its not syncronised as the diaphgram in the pump has ruptured then it wont supply enough fuel when you try and rev it so you engine rev go all over the place as the flow of fuel is not constant. IMHO!

Fuel problems are always quite difficult as some of the symptoms above can also happen if your fuel filter is ready for a change i.e.(full of water and gunk) or if you have a split fuel pipe thats sucking in air...

The ultimate problem is its usally undrivability!

Excessive smoke, but still drivable sounds more like injector problems, piston ring oil leakage... timing out... the list goes on... there are loads and loads of topics on people problems with fueling etc. Best thing to do is try and list the symptoms as best you can and what you have checked already.

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Many thanks for the comprehensive reply. I see what you mean. Thanks for taking the trouble to explain it to me.

I am having a bad year for smoke and bad running. Earlier in the year the Defender failed the ITV (Spanish MOT) on the emmisions test. It turned out that the timing tensioner (300tdi) had failed and the belt had slipped. I had that sorted (new belt etc.) and passed the test, but a couple of months later the running deteriorated so much that it had to be taken by breakdown truck to my local LR expert. It was just before a long holiday, but he checked the injectors, found them coked up, put a good set in and all seemed well. The only problem I then had was white smoke when the engine was cold. He fixed that by tweaking the timing. Now the Defender was running well - no smoke and plenty of power. Then last week it was time for another ITV test - 6 monthly here for 4x4s over 10 years! So, to make sure it would pass the emissions test I added some MOLY "Stop" to the fuel. It passed the test - better than the opacity reading last time, but I now have whitish smoke, with excessive black when working hard. I wish that I hadn't added the MOLY stuff, because it is probably giving confusing symptoms. I am now hoping that by flushing out the tanks (by using up the fuel) and using good quality diesel and an injector cleaner I may get away with not having to switch injectors again. Because the engine is running reasonably I may be able to "drive" the problem away! But, perhaps I should just take a look at an injector to see if they are partially coked?

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