Injector noise / chatter (aka why's my HDi so noisy?)

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FlySpeck
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Injector noise / chatter (aka why's my HDi so noisy?)

Post by FlySpeck » Sat May 08, 2010 6:12 am

The noise you get on the hdi between 2k and 3.2k rpm, as previously discussed, seems to be an injector issue, mine does it and cleaning agents have only improved it slightly. What I am wondering, is has anyone determined if what is happening is the injector is blocked partly and does not do the pilot injection burst - hence combustion is louder, or is the injector solenoid rattling (less likely I think now) or is the injector spraying weakly at those revs for some reason connected with the pilot injection, and hence its pinking (pre ignition) - tho thats kinda how diesels work anyway so I wouldnt think pinking would be as bad as on a petrol....but anyone know better about this?

Its getting on me goat so I want to understand whats happening, even tho I will be getting an injector this weekend and swapping out till I cure it.
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Re: Injector noise / chatter

Post by steve_earwig » Sat May 08, 2010 6:31 am

I think we're fairly decided the noise comes from the upper part of the injector, so changing the tip doesn't help (not even sure you can on these stoopid things). I'll be very interested if you get a result from this as mine are so loud now I can hear the noise bouncing off buildings as I drive past :(
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Re: Injector noise / chatter

Post by eoin27 » Sat May 08, 2010 9:42 am

Oh the unpleasant disiesel memories.

Tip, put £8-10 of petrol in with a full tank. Petrol cleans the crap out of injectors. A lot of diesel additives have petrol in them
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Re: Injector noise / chatter

Post by FlySpeck » Sat May 08, 2010 12:36 pm

I may just do that - any issues with seals / HP pump etc? Steve?

I will let ya know about my findings as Im determined to fix it - mine sounds like a stick running along a metal railing LOL....but after 3k, oh the silence!!
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Re: Injector noise / chatter

Post by steve_earwig » Sat May 08, 2010 1:04 pm

I think it's Welly who reckons early lift pump demise is often due to filling it with petrol :?

Mine just sounds like a petrol that's badly pinking above 3.2k. Under that it sounds like my camshaft's had it.
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 9:19 am

what got me thinking was it just sounds like a normal diesel (non hdi / pilot smoothed) so I began to think the pilot injection is not happening on one or more cyls, hence the increased dieselling noise. HDi's are specifically designed as you know, to sound very very quiet because of the pilot injection phase.

Noisy solenoids dont sound like diesel "rattle" but all normal (non hdi) Di's are harsh sounding without pilot injection....

SO....maybe one injector doesnt spray during the pilot phase, but only on main injection....so doesnt quieten that cyl and you hear the combustion rattle?

Now, the HP rail is constantly held high, so the only way to achieve PI spray is to send a very short early burst signal to each injector using the normal nozzle holes, or have a dedicated extra PI hole that is used in concert with the 4 main holes on the nozzle, as the bosch hdi injectors are constant-variable type its likely they use a reduced signal to cause a small amount of fuel to begin injecting on the pilot phase, then increase the spray to full bore during each firing point. This could mean the needle isnt lifting on the small PI phase but when asked to go full bore at TDC, it does. That would mean the solenoid itself isnt rattling, but rather not supplying the smoothing PI spray for whatever reason, lazy needle, sticky solenoid so small force causes no movement, or a partially blocked nozzle that only sprays on full pressure.

Dont fancy adding petrol really, as its obviously aggressive compared to derv and may just bugger the seals on the pump as you say.
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Re: Injector noise / chatter

Post by steve_earwig » Sun May 09, 2010 9:32 am

Looking about and you're right, the engine cuts the pre-injection off at 3,200rpm, so it's bugger all to do with this third piston malarkey.

So, what's next? It's still looking like new injectors from here :(
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1991 Yamaha TDM850 - fuel leaks galore!
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Re: Injector noise / chatter

Post by DiscoPol » Sun May 09, 2010 9:52 am

*is watching this thread with great interest....but sadly with no real input*
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Re: Injector noise / chatter

Post by steve_earwig » Sun May 09, 2010 9:57 am

That's the same everywhere, I've been Googling (yet again) and there's loads of people with the same problem but nobody's got any solutions :(

What gets me is a big thing is made about this pre-injection reducing engine noise by 3Db!! - and then it seems to be actually generating more noise once the engine's got a few miles on it :shock:

How the feck do we turn it off??
Unskilled meddling sin©e 2007

2004 D9 2.0 HDi 110 Estate lhd VF38ERHZF81657352 - sold but being very well looked after.
1991 Yamaha TDM850 - fuel leaks galore!
2008 Toyota Recall4 2.0 VVTI ATM LHD JTMBH31V90D007261 - flimsy piece of crap.
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 11:07 am

thats precisely where I ended up with this!

I wondered if the pre-injection can be switched off or on at will by changing a setting in the ecu, or disabling it mechanically / electrically etc so it doesnt do it, as after 3200 rpm its automatically turned off and the engine sounds sweet! I suspect that figure is chosen as the engine is already almost right on top of peak torque at that rpm and perhaps there isnt time to pre-inject as the rpm increases above that level?

The other alternative is nozzle blocking which may be repairable on the bench. The solenoid part of a bosch injector is horrendously complex and not to be opened at any cost! But...the nozzle end is simple to dismantle and perhaps clean - with surgical spirits or white spirit which will both break down oil and diesel wax deposits.....the holes are tiny but then so are welding nozzles in some cases and you get some pretty small nozzle cleaners from welding supply places.

Just a thought so far ;)
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Re: Injector noise / chatter

Post by steve_earwig » Sun May 09, 2010 11:32 am

But isn't that what these injector cleaner additives do? Or something a little stronger perhaps. Hey, there's so much volcanic dust about these days...

Presumably as pre-infection is such a feature of these HDis it's not going to be so easy to get rid of :(
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 11:50 am

yep. plus anything that injects at 1350 bar (over 19,000 psi!!) must be pretty hard blocked if that kind of pressure can't shift it, but the holes are extremely small so any particle or deposit bigger than them on the inside will plug it good. That would suggest aggressive cleaning on the inside of the nozzle (one-shot acid or somesuch) may shift it.

(All makes and models of HDi (not just pug) use pilot-injection, and for instance the latest audi PD diesels have a cam driven pump/injector combo on each cyl, driven by a tiny 10mm camshaft, so they cannot do pilot injection, and hence are rattly.)

I reckon that more info is needed, but that somehow I think we should be able to try disabling PI or trying to find a way to replicate what happens above 3200 rpm and force it into that way of working and see if the noise disappears....its using engine load sensing, which is maybe throttle angle to rpm, cant be vacuum on a diesel, if we can find out what its looking at to decide when to start and stop PI then we can block the signal and get a quiet engine.

The conundrum seems to me to be why does it shut up after 3200 if the so called quietening effect of the PI has been shut off? Sounds more like its working backwards - not on when it should - and on when it shouldnt - faulty engine load sensing???

Doesnt make sense. More googling required haha
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 12:28 pm

Some interesting background info (not all pug)
TDCi is also equipped with a piezo electric knock sensor of the type used in gasoline engines, fitted to the block between cylinders two and three. According to Lake, the sensor's job is to detect any conbustion harshness by measuring the "signature of the combustion event". When this event occurs, the sensor signals the IDM and EEC-V modules, which then modify the injection process to smooth out any unwanted peaks of high pressure. Ford calls this function 'accelerometer pilot control' and it is one of several key features of the TDCi engine.

Another feature lies in the strategy for maintaining integrity during ageing. The injectors are given what Ford calls 'individual injector characterization' by a matrix code assigned during manufacture. Each code is scanned and programmed into the ECU, customizing the injection pulse timing and duration on a cylinder- by-cylinder basis. More importantly, the system allows each injector to be individually and continually re-calibrated, overcoming any problems caused by wear as they age.

The bottom line though, is that the precisely-metered multiple-pilot and single-post injections enable the TDCi to avoid sharp rises in cylinder pressure that cause the clattering noise. Frank Foehner of Ford's NVH center in Cologne thinks such control is a real achievement and
says it will allow NVH engineers to achieve impressive linearity of sound versus increasing engine speed and load.
Another:
Leading these is the introduction of the first closed-loop control system for diesel engines; called Accelerometer Pilot Control (APC), which allows the Engine Management System to analyse the quality of the combustion. Information from the APC allows injection to be adjusted as conditions change, ensuring that the system is always correctly calibrated.

The major benefit of APC, combined with Delphi's new generation, fast- acting compact solenoid injector, is that it allows exceptionally precise control of pilot injection. These tiny volumes of fuel, injected before the main injection pulse, smooth the start of combustion, eliminating the pressure spikes that produce the 'clatter' associated with previous generation diesels.

Existing technologies can provide a single pilot-injection event with a volume of around 1-2 cubic millimeters at low injection pressures, but typically suffer from reduced metering accuracy during their life on the car, at idle or higher pressure. Engine designers need both low pressures for quiet idle and higher pressures because this allows cylinders to be fuelled more quickly and to have a better spray pattern, leading to improved torque and reduced smoke. The Delphi system allows pilot volumes across the pressure range that remains stable between injectors throughout the engine life.
Accelerometer Pilot Control (APC) "listens" to engine combustion and adjusts the injector drive pulse to help the engine, over its life, maintain consistently clean, quiet and smooth running
Does the pug HDi have a knock sensor Steve? Thought you might be able to look up your magic catalog lol

The knock sensor, if it has one, may be deaf! That would explain a lack of pilot injection if its not happening when it should. Would expect that to produce an EML but maybe not, as its only making the engine quieter, not affecting emissions or causing damage like on a petrol turbo...
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 2:33 pm

ok, further reading here says that a knock sensor is used to measure combustion noise and hence start pilot injection (if required dep. on combustion noise levels) using the same solenoid that drives main injection, and that the knock sensors do no other job than signalling PI is required - which means the injector solenoid, if faulty, would not work normally either, and if noisey itself would be noisy always:

http://www.pdfone.com/download/83_relat ... n-in-a.pdf

So I think we can say the following should be true:

1. that the HDi must have knock sensor(s)
2. that they control the use of PI (Pilot Injection)
3. that a very very small amount of fuel (1 or 2 cubic mm) is used for PI

In short, I think either the original faulty injector theory is right but is down to nozzle blockage (less likely as they still pull well and go quiet after 3200 rpm) - or the knock sensor has become more hard of hearing (or deaf) so PI doesnt occur when it should (maybe on one or all cyls) and that there is usually one KS mounted between 2nd and 3rd cyls on most Di engines, and it wont throw a code if it fails, cos its not critical to running the engine or the emissions it produces, but simply to quieten the sound of a Di for driver comfort / making Di's more attractive in passenger cars...

Now....wheres the flippin knock sensor on the pug HDi....

Oh and btw -3db drop on a noise (or any signal) is equal to reducing that noise by half - as per the Logarithmic Law. They are referring to a reduction in noise signal of the combustion signature by -3db not a drop of 3 decibels of sound pressure level (there are 2 db systems used in engineering, look the same but dont mean the same lol)
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 3:17 pm

HA!!!

This PSA doc shows pictorially on page 2 that the same solenoid action & nozzle is used for main injection as well as pilot injection, just a tiny pulse is delivered for PI compared to the high double pulse for main injection.

http://www.pdfone.com/download/5_keywor ... -s-dpf.pdf

Which means in our case, either the small pulse doesnt arrive at all (faulty knock sensor not detecting noise, high resistance at injector terminals or poor injector ground maybe) and only the high voltage pulses for main injection fire the solenoid....... OR ........that the solenoid becomes stiffer somehow and or encounters increased resistance of the needle assembly, so the small pulse does not lift the needle and hence no pilot spray is performed...
2001 406 HDi 90 LX saloon with moon miles...

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