OT: Pinking Diesel Engine

[The Natural Philosopher]

Don't change the subject.

How do you propose anyone 'checks the timing'

[The Natural Philosopher]

Oh no, you claim to be the expert.

How would you 'check the timing'' on a diesel engine?

[The Natural Philosopher]

Depends on the Land rover

[The Natural Philosopher]

First tell; me what you thing determines the 'timing' on a modern diesel, and how you can 'measure' it, and how you can 'change' it.

[Fredxxx]

Then explain why you say "Do you actually know how the injection timning works on a modern diesel" after he said get the timing checked.

Are you suggesting you don't know?

[Fredxxx]

After you said "Do you actually know how the injection timning works on a modern diesel" you seem to be claiming that ground.

Are you suggesting you don't know?

[Fredxxx]

Obviously young enough to have a ECU.

[Fredxxx]

We were all hoping you'd be telling where Mr Cheerful statements might be wrong.

Do tell...........

[Clive George]

I suspect he does, because he's given the correct answer. If the injection starts early, it'll pink. It can start early if the computer thinks the crank is in a different position to where it actually is.

[Fredxxx]

We don't know yet the engine the OP has, whether its high pressure rail or a hybrid, old pump but still drive by wire. The OP said the EMU was replaced, but I'm wondering if this was really the EDU associated with his pump or some other on-board control unit.

Without more info Mr Cheerful's answer is the right one.

[polygonum]

Not with you there - how can what the computer thinks affect the physical state within the cylinder? The computer could ...

Bomb#20: In the beginning, there was darkness. And the darkness was without form, and void.

Boiler: What the hell is he talking about?

Bomb#20: And in addition to the darkness there was also me. And I moved upon the face of the darkness. And I saw that I was alone. Let there be light.

But how do the ECU's thoughts impact on the detonation?

[MrCheerful]

The start of combustion is NOT triggered by the level of compression.

[Fredxxx]

That does depend on the position of the crank sensor and whether this has been correctly programmed into the ECU. We still don't know the OP's engine so not sure what this has to do with bombs and boilers.

There are generally a few fault codes associated with injection timing. I have read articles that under a fault condition the fuel pump goes to full advance on certain types.

[MrCheerful]

Please enlighten us.

The principal of the diesel engine has not changed since it was invented, it needs correct timing to run properly, and incorrect timing can wreck it. Can you explain what you infer is wrong with these statements?

Please tell me why the timing cannot be wrong.

[newshound]

+1

[Peter Hill]

The ECU was given the attribute of thinking. Computer consciousness is quite still not reality.

The "Bomb#20" in question was a character in the film "Dark Star". It's power of thought caused some problems, it wasn't very interested in doing it's job of detonation. A "pet" that resembled an animated beach ball with duck's webbed feet also caused problems.

He could have gone for HAL in 2001 .. more trouble.

Or Skynet .. guess what?

[Fredxxx]

I feel much wiser - thank you.

Of course Dark Star must have been before I was born!! What's 2001? :-)

[NY]

Because the detonation begins when the fuel injection begins - and if the crank-position sensor thinks a given piston is in a different position it will inject the fuel early or late of the correct position of the piston.

[NY]

I'm wondering whether Polygonum (I think, if I've got the quoting correct - if not, apologies) thinks that detonation *is* triggered by the compression reaching some critical level - in other words, that fuel is injected arbitrarily early and then detonates when the pressure and/or mixture temperature subsequently reaches the "right" level - which is not how it works.

As I understand it, air (and nothing but air) is sucked/blown (*) into the cylinder on the inlet stroke, and is compressed on the compression stroke which raises its temperature above the point at which fuel will spontaneously ignite/detonate if it comes in contact with the air. At the correct moment (which may be x milliseconds rather than y degrees before top dead centre, fuel injection begins. The fuel ignites as it comes in contact with the air and continues to burn for as long as the fuel is injected.

The correct instant of injection is determined by a TDC sensor which the ECU uses as a reference point to determine the time offset to the injection point, based on engine speed so fuel injection will always have *finished* before the piston reaches the bottom of its travel on the power stroke and the exhaust valve opens, since any fuel injected after this time will not increase the cylinder pressure (and hence contribute to engine power) but will instead go straight out of the exhaust.

(*) Depending on whether engine is normally aspirated or turbo/super charged.

[NY]

And this changes when the crank sensor is changed - as I found out when I took my car to the local garage in my village to have the cambelt replaced at the stated mileage. The replacement of the belt was straightforward but the associated sensor needed to be replaced as well. I'm not sure whether the old one broke during removal of the old belt or whether the sensor replacement was a routine part of belt replacement.

The garage took five days (!) to manage to reprogram the ECU for the fact that the sensor had changed and either gave a different voltage-versus-time curve as the TDC was reached or else was in a slightly different position. The change in timing of the critical TDC event was enough to prevent the engine running properly and they had to call out someone from Peugeot to advise on adjusting the ECU to compensate.

The engine ran perfectly once they adjusted it properly (it ran for another

30,000 miles until I sold the car) but it took a long time for them to get it going. I happened to be cycling past the garage late one evening to go shopping (after five days without a car I was running out of things) and they were still working on my car and trying to start the engine. Suddenly I heard a yell of delight as it fired - and carried on running smoothly. I stopped to see how things were going and the engineer was dancing round the room and punching the air in delight.

I stopped using that garage after this incident, and an earlier one where the garage had replaced a broken "fan belt" and the replacement failed a thousand miles later because they hadn't diagnosed the bent pulley flange that had *caused* the original belt failure, and wouldn't give me any refund for shoddy workmanship that required the work to be repeated.