HDI rattling heard when accelerating

[dnsey]

I agree that it's probably normal Diesel knock.
Put your mind at rest by replacing the undershield (it's only a 10 minute job!), and the upper acoustic cover if it's missing, and have a listen then. All that soundproofing was fitted for a reason

[CitroJim]

All that soundproofing was fitted for a reason

Quite

I'm still running mine without an undertray, mainly because I've not sorted out a couple of damaged mounting studs

I know that removing the undertray was what really alerted me to a boost leak on the turbo. It sounded like a howling gale under accelleration yet was inaudible with the tray in place...

[Peter.N.]

I would agree with Jim, in fact modern direct injection diesels actually inject a small ammount of fuel in advance of the main burst, this ignintes so that when the main charge enters it doesn't suddenly detonate which is what gave old IDI engines their characteristic knock.

Direct injection engines are by nature noiser than IDIs and without electronic control they still would be. If anyone remembers the first Perkins direct injection engine the 'Prima' having mechanical injection it sounded as though all the big end had gone so they introduced two stage injection - mechanically which was very clever and that made a tremendous difference. Remember the first DI transits?

On the old Perkins 4/108 engines the crankshaft would break if it ran for long with over advanced pump timing, I know, it happened to me three times! But that only had a three bearing crankshaft, such things don't usually happen now.

A diesel engine is built to withstand the sudden increase of pressure on ignition, a petrol engine isn't and will suffer as a result of pre ignition, compare the weight of the two engines.

Getting back to the original post, my 406 knocks when cold, sounds like only on one cylinder at the moment but I'm not intending to do anything about it as I don't regard it as a problem.

Peter

[CitroJim]

Remember the first DI transits?

Oh yes They sounded like a river of spanners flowing over a waterfall...

That the HDi is so intrinsically quiet and smooth is a testament to fantastic design work. Some later diesels, notably Poxhall, VW and some Japs still haven't quite cracked it from what my ears tell me.

My neighhbour has a near-new diesel Poxhall Septum and that sounds like a bag of spanners on a cold morning, as does one of my other neighbour's Mitsubishi Animal ute thing. It's hard to start, smokes like a chimney and sounds as rough as guts when cold and hot. It's not that old either... It's breathtakingly ugly too. Even he detests the wretched thing...

[Dommo]

I think you'll find petrols do have EGR. I thought I'd seen it on a few cars, but I know for definite that I have seen it on a 1.6 Audi A3 in my mates yard, he's a mechanic and was doing the head gasket on it.

[RichardW]

Rather than suffering pre-ignition, all diesels exhibit a condition known as ignition delay where a finite time elapses between injection and the onset of combustion. Diesel has a fairly low flash point. Above this temperature diesel will spontaneously combust and it's ability to combust will not be changed by being in a very hot combustion chamber; if the temperature is above flash point then diesel will go bang. That's a fundamental principle of a compression ignition engine...

Since we're having an in depth technical discussion.... that's not quite right, Jim Flash point is the temperature at which a liquid has a high enough vapour pressure to support self sustaingin combustion above it (it being the vapour and not the liquid that burns). For petrol this is well below 0degC - for diesel it is much higher, above 60degC certainly - put a match to a bowl of diesel at ambient temp and it will go out probably. The property of interest for diesel engines is auto ignition temperature - the temperaure at which the fluid spontaneously ignites - this is around 200 degC, a bit lower than petrol.

DickieG - what did you do to disable the EGR?

[CitroJim]

Thanks Richard You're absolutely right! Schoolboy error there

[DickieG]

DickieG - what did you do to disable the EGR?

Removed the vacuum pipe running to the EGR solenoid (the one nearest the front of the car) then bunged up the vacuum hose with a screw, this is important to avoid vacuum leaks which will cause problems with the turbo solenoid. I also fitted a short length of hose to the solenoid and bunged up that the same way to keep it clean inside, you can just see it in the top left corner of the following photo where the black hose with a blue and white ring on it is hanging down. If you unplug the electric plug you'll get fault codes and possibly cause the engine to run in limp home mode.

[Chris570]

All that soundproofing was fitted for a reason

Quite

I'm still running mine without an undertray, mainly because I've not sorted out a couple of damaged mounting studs

I know that removing the undertray was what really alerted me to a boost leak on the turbo. It sounded like a howling gale under accelleration yet was inaudible with the tray in place...

and you wonder why your hdi runs cool.....

would go some way to explaining why mine is quieter too

[KevMayer]

I've been looking into this 'pinking' issue that I menyioned earlier and I've found some interesting info which I'll run past you.

When I blanked the EGR pipe on my 2.2 Hdi I definatelly got a vibration under moderate acceleration which I found quite worrying at the time and it sounded like pinking and i suspected the timing was over advanced.

I've read a conversation on the forum of "Ecomodder.com" and here's a quote from one of the chaps:-

Quote:-

Okay, here's why you have trouble when you disable the EGR. When the system is polluting your fuel/air charge with exhaust gases (something racers have been doing their best to prevent for, oh, eighty years or so) it makes the mixture harder to light and slower to burn (and cooler-burning, which cuts nitrogen oxide emissions). So the ignition advance curve was modified by the manufacturer for more advance to light the fire earlier. If you disable the EGR, you now have an over-advanced ignition, and you'll likely get ping, maybe a lot. You could temporarily stop the ping by disconnecting the vacuum advance (and plugging the line). That's bad for fuel economy, however, so what you really need to do is re-curve the dizzy for less advance in the range where the EGR used to operate.

End quote

I've also seen other diesel related threads which talk about EGR systems needing/using advanced timing angles.

So, It appears that the ECU advances injection timing when EGR is active or at least when the ECU thinks it's initiated the EGR. So, if the EGR valve is opened but the pipe is actually blanked then the ECU is still probably advancing the timing, but, now the engine has a fast burning fuel/air mixture and this is probably what caused my pinking noise.

It's some way to explaining to me why my engine used to rattle with the EGR blanked and explains how a faulty EGR may cause a rattle.

I'd be interseted to hear what you think about this.

p.s. I didn't know Citrojim knew words like 'bollocks'. Such a clean living upstanding chap he is too

[myglaren]

p.s. I didn't know Citrojim new words like 'bollocks'. Such a clean living upstanding chap he is too

Jim doesn't. It's the forum Nanny working in reverse

[CitroJim]

p.s. I didn't know Citrojim new words like 'bollocks'. Such a clean living upstanding chap he is too

Jim doesn't. It's the forum Nanny working in reverse

It's not even that I've been spending too much time with Chris570 working on an XM... I blame him

Kev, seriously - I've been giving some thought to all of this and will comment later...

[Chris570]

p.s. I didn't know Citrojim new words like 'bollocks'. Such a clean living upstanding chap he is too

Jim doesn't. It's the forum Nanny working in reverse

It's not even that I've been spending too much time with Chris570 working on an XM... I blame him

Kev, seriously - I've been giving some thought to all of this and will comment later...

Not my fault the XM was designed by a Mr S Wonder and R Charles after a very heavy drinking session

[charentejohn]

Good news, well for me anyway, I was pulling on to a dual carriageway on a steep slip road. A red mist came down and I realised I was doing 3200rpm in 2nd and.........silence. So looks like it is just Injectors and they were quieter in general today than last time I went out so hopefully will improve as the tank of diesel+additive is run through.
Was warmer today though, also no white mist / smoke as engine warmed up. Probably just temp and less condensation in the exhaust but also good news.

Other upside is that I now know about the potential aux belt pulley problem so will change it when an opportunity permits. Luckily no urgency but, as said, I will do the paint stripe test. Just goes to show all info is good info as it throws up things I would never have considered otherwise.

[KevMayer]

That's good news.

So, panic over. It was Professor Plumb, in the Library with a Candlestick.