HFM??

brake assistance is either not there as standard (not very common these days) or is provided by a vacuum powered booster (servo) or an electrically pumped system particularly on many ABS cars . Many diesels use an engine driven pump, often on the back of the alternator or elsewhere depending on maker.

Yes, hence why they used to be called 'Servo Assisted Brakes'.

There must be something there amplifying whatever pressure it is you're applying to the pedal, especially on a hefty car like an E Class.

No negative inlet manifold pressure hence no vacuum to operate the servo.

It's a hydraulic pump instead. A la Citroen.

It's brake by wire - SBC.

Yes, but the pressure's generated by an electro-hydraulic pump, not a vacuum servo.

All, afaik.

Nedavno Duncan Wood napisa:

???? This is interesting. I thought it's the same as petrol engine. Any links explaining this?

And Happy New Year to you all.

diesels work by compressing air to make it hot so that when fuel is injected into the hot air it will start to burn. The air intake is usually open or only partially throttled (otherwise insufficient air would get in to be squashed and get hot) The power is varied by the quantity of fuel injected.

Nedavno Mrcheerful napisa:

This I did not know. And what happens when you turn the key in ignition to shut the engine off? You cut off fuel? Any difference new -old cars? Someone told me that you cold pull all wires out of Mercedes W123 diesel engine, and it will still run :-)

Yes a fuel cut off solenoid shuts it down but it's quite an experience when you have a turbo oil seal fail and end up with a "runaway". With a manual you can stall it but I wouldn't like to be in a auto when that happens!

With ancient diesels, turning the key off left the engine running. You had an engine stop control, which was much like a choke knob on an old petrol car. This operated a mechanical stop lever on the injection pump.

With many of those ancient things, provided it wasn't cold enough to need the glow plugs, you could run one with absolutely no electrics at all. Tow it to start, stall it to stop!

Less ancient diesels replaced the knob and cable with an electrical solenoid that also stopped the supply at the pump.

Modern diesel injection systems are more like electronically injected petrol engines; turning the key off will stop the electrical supply to the injectors.

Chris

Yes. There's a shut-off solenoid on the injection pump on older diesels.

Newer ones have electronic control of everything- so yes. I'd imagine the fuel is still cut off, but how you do it would be different.

I'd imagine so long as the shut-off solenoid was open (or disabled) it would still run- but the solenoid is electrical usually.

Yes. Usually there's a cutoff solenoid. This is why it's important if you've got a turbo diesel not to have an oil leak on the turbo because it keeps the engine running and if bad enough, can cause the engine to runaway, it only stopping increasing in speed when it grenades.

Yes. On the really really old ones, you pulled a wire which closed a valve on the fuel injection pump.

In some specialist applications, like for vehicles in very cold places like the Arctic or Siberia, batteries just won't work in the cold - the chemical reactions are too slow.

What they do there is have diesel engines and use compressed air or even explosive(!) starters to get the engine spinning and firing, so they run with no electricity at all, just a mechanically driven diesel pump.

Nedavno PCPaul napisa:

Yes, I remember that when I was in the army we had some Russian vehicles that had tanks for compress air! And I even managed on one occasion to drain batteries on one of them completely, and since it was

10 ton vehicle, you could not jump-start it, and compressed air worked!

The TDI's.

Tim.

Anyway, they fitted a new one - total bill £210 - without telling me first.

HANG ON, SO THEY FITTED ONE?

£210 is a lot of fooking money for an alternator, even with main dealer labour so I do a bit of ringing around.

Well my favourite reconditioners won't even touch them as they're such a bastard to do so that kind of got me a bit worried. Phones a few factors to be told it'll be between £140 and £170 depending on which one of 4 it is that's fitted to my car.

So..potters off to the main dealers and gets the bill. £114+VAT for a brand new genuine Ford alternator. FUCK ME, THAT'S CHEAP. 1.5hrs labour for investigation and fitting.

Turns out I got quite a good deal. Bit of a heart attack with the labour but you need a special tool to relieve the aux belt tensioner in the first place (could do it with a 1/2" ratchet but the engine is too close to the inner wing to get it in) and it's still a good hours job just to change the belt.

AND THEN SO DID YOU??

Explained to the woman who had rung me that I'm used to £50 for a Capri alternator and it being 10 minutes to swap it over - 5 of that spent putting the kettle on for a brew when the job is done, so it came as a bit of a shock.

Not really maintenance, is it? More like uk.rec.'take it to the dealer'