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Don't worry about running out of fuel,if you do,just put some more in and turn the engine over on the starter and it will fire up again.If it won't start there is a pump on top of the fuel filter that you can manually pump to prime the system if required.Most definitley not a garage job!
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Ha! Funny you should say that Chris.
I had noticed that when "flooring" it (theres a particularly BAD roundabout where you have to dart out over 3 lanes to turn right or otherwise bring your jamas for the night) where it seems to loose power fully depressed but yet picks it up if I slightly decelerate (sp?). I noticed this as it lurched forward a few times when I'd got where I wanted to be and started to lift my foot back off.
Cheers!
Patricia
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Patricia,
So you can impress(?) your friends - petrols are spark ingnition and diesels are compression igniton. This means that a petrol engine needs a spark to ignite the fuel, whereas a diesel does it simply by heating the air in the cylinder, by compressing it, to a temperature which is high enough for the diesel to spontaneously ignite. When cold the engine needs a bit of help as all the heat leaks away into the cold engine - this is what the glow plugs are for - they glow red hot and the diesel is squirted over them, causing it to go bang! A modern diesel with glow plugs in good condition should start at the first cylinder over compression - ie almost as soon as you turn the key.
Modern diesels are almost all turbo charged (yours is!) This means the exhaust gases are used to drive a compressor that forces more air into the engine: more air = can burn more diesel = more go! Turbos require good oil, changed regularly as they run very hot (700+ deg C) and very fast (100,000 rpm)! When turning the engine off, make sure it has come to idle, and do not blip the throttle - this causes the turbo to spin up and then run down with no lubrication - bad! After a long hard run (eg coming off the motorway into the services) allow the engine to drop back to idle and leave it running for a while to cool the turbo down - this prevents the oil turning to 'coal' inside the turbo - bad again.
Peak torque is usually around 2,000 rpm, so select a gear to try and drive at this engine speed where possible - this will also give you maximum available acceleration to get out of difficulty if you need it (and probably minimum fuel consumption!). Every so often take it above 4000 rpm, this frees up the engine, and helps to dislosge any soot particles in the exhaust (which otherwise build up and come out in a BIG black cloud when you do give it some welly!)
Don't worry about running out of diesel - it's not the end of the world, just a bit of an annoyance! It might start again just by cranking, but needing to prime it is more likely - diesel do not have fuel pump at the tank end, so the fuel needs to be brought up to the injection pump before it will start.
I have noticed the speed up on lift off as well, but have no real explanation for it - maybe the pump is injecting too much diesel, and the engine is choked? If you want to make a quick getaway, rev it to about 3k then let the clutch in - this will spin the turbo up and make sure you get boost and therefore acceleration when you want to!
The useable rev range is more like 2000 - 4500 rpm, with most go above 3000 rpm - if you want to press on make sure you are in a gear that puts you in this range - and change up - do not be tempted to hang on to gears as you would in a multivalve petrol - it doesn't do any good!
When manouvering no revs are necessary - just treat the clutch gently and it will go along at tick over no problems - great in traffic jams - you can drive along, feet off the pedals, at 10 mph, even uphill - give it a try! Really annoys the petrol cars, 'cos they can't do it and have to slip the clutch all the time!
Enjoy the more relaxed driving experience once you have adapted (and find you can't drive a petrol anymore - they just stall all the time - last time I tried I stalled it 3 times - getting it out of the carpark!)
Richard
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RICHARD!!! That made SO much sense! Thank you very much. I actually understood about 99% of what you said and there was lots in there that I didn't know.
A few questions if thats ok?
"make sure it has come to idle, and do not blip the throttle " [b] What does "blip the throttle" mean? [/b].
What on earch is "Peak Torque"? Sounds like a ice-skating move to me? ;)
What do you mean by "do not be tempted to hang on to gears as you would ina multivalve petrol? I've always be taught to get into the highest gear as soon as possible (in relation to the speed you're doing) so that you're not over racing the car. Is that what you mean I should keep doing in the deisel?
I didn't know it would run so slow in traffic jams - I really do think I've been driving it like a petrol engine - will I have caused any damage? I do drive quite gently in residential areas. Im a bit of a speed-o on the m'way usually staying at 85-90 with the rev on about 3.5. However, I have found that if I do go too slowly for 2nd or 3rd gear, the red "stall" light comes on. So far, it hasn't actually cut out on me but I have changed down very quickly - hope thats ok.
Again, thanks so much, it was REALLY much appreciated!
Patricia
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>What does "blip the throttle" mean? [/b].
Pressing and quickly releasing the throttle - a few years ago it was common for people to do this as they switched off the engine - don't know why.
>What on earch is "Peak Torque"? Sounds like a ice-skating move to me? ;)
No, nothing to do with ice skating! It's the point in the rev range at which the engine is producing the most torque - in diesels this is typically around 2000 rpm and often coincides quite nicely with the lowest specific fuel consumption (unit of fuel burnt per bhp of power produced).
>do not be tempted to hang on to gears as you would ina multivalve petrol?
Holding onto gears when you accelerate and taking the engine all the way to the red line - multivalve (eg 16V) petrol engines often need revving to beyond 4000 rpm before you get any real power, so you hold the gear to the red line then change up so make sure you're still above 4k revs. Not necessary in a diesel as it will pull from 2000 rpm or so. Also diesels do not really like sustained very high revs as it tends to overheat the pistons (no cooling effect from the fuel evaporating as their is in petrol engines). Your technique sounds OK, but do not be tempted to 'labour' the engine, ie keep it going too slowly - anything below about 1500 rpm requires a down change.
3.5k on the m-way is OK, although I obviously can't condone speeding.... Getting the red lights on means you are asking too much of the engine - change down in anticipation!
Richard
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Excellent write-up, Richard. There is just one thing that doesn't look quite right and you may agree with me on this or, if I've got it wrong, you might like to explain why.
Diesel fuel, like all fluids, is virtually incompressible and this attribute is vital for injection to take place. Any air in the system acts like a cushion and prevents the fuel injecting.
Injection pressures need to be anything up to 30,000 psi, or 2000 bar, and this cannot be achieved if there is air in the system. This is why it is vital to exclude all air; nothing to do with having no pump at the tank end. Also I believe that the fuel needs to be brought right up to the injector, not just to the fuel pump.
I now have a question for T Lucas regarding his/her claim that running out of fuel is no problem because you simply fill up and turn the engine over on the starter, or otherwise just use the pump on the filter. Are you SURE that this applies to ALL diesel cars? It certainly doesn't apply to a lot of industrial & construction equipment diesels where the only answer is to slacken the injection pipe at the injector end to let the air out, and even then it can be quite a long job. I do know of injection pumps that are self-priming but you still need to get the air out of the injection pipe, otherwise it just compresses and decompresses without budging. Any comments welcomed -- I'm still not too old to learn!
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This is really interesting, as I am needing to learn more on diesel fuel systems.
Can anyone point me towards a website with explanations of the mechanics of a diesel engine, common-rail, HDi, PD and other diesel terms.
Thanks
Simon (Anne's Other Half)
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Can anyone point me towards a website with explanations of the mechanics of a diesel engine, common-rail, HDi, PD and other diesel terms.
www.howstuffworks.com/
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Dizzy,
Yeah, I agree with the incompressibility bit, but 2000 bar is reserved for the lateset common rail etc engines - 130 - 150 is more normal for an indirect engine. Now, as to the lift of fuel, my thought is that:
a) the Diesel injection pump is closed circuit - it only pumps what it needs, if you've got to fill the entire fuel system this takes a long time (On a petrol engine the pump is massively oversized so gets the petrol up quite quickly).
b) The injection pump is a precision machine, and needs good lubrication - cranking it for ages without diesel is not going to do it any good.
I reckon that eventually you will shift the air out of the injector pipes (it can't expand backwards because the new diesel is pushing it up the pipe again!), but agree it takes a while (starting my BX TD after I had the head off took A LOT of cranking!).
Richard
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