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

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Re: Injector noise / chatter

Post by steve_earwig » Sun May 09, 2010 3:31 pm

Oh blimey :? It's confirmation day here, I've just escaped from one such party next door and if I see any more food today I'll explode.

No knock sensor that I can find. If the injector didn't see the small pulse or didn't react in time then there wouldn't be a marked change at 3,200 rpm, unless it's too much fuel being delivered...

I did see some stuff about poor spray patterns at small injector openings (eg PI) due to excess movement causing problems, could this be wear in the injector itself?
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Re: Injector noise / chatter

Post by FlySpeck » Sun May 09, 2010 4:16 pm

could be wear indeed, maybe the solenoid becomes sluggish to move off on very low voltage pulses, so it fails to send the PI fuel. Crazy thing is we are talking about the injection of a cubic millimetre of diesel here for PI to work!

would be interesting (but difficult) to 'scope the injector signals under acceleration on a rattling engine to see if the pulse ever arrives or not, and if it does, then the injector is at fault...if not, the ecu / wiring / grounding must be to blame.

According to pug docs I read, after 3200 rpm the main injection advance climbs so rapidly as rpm's increase beyond this level that the pilot injection would effectively be "lost" and so is no more use - then nature of the common-rail engine is to run quietly at high rpm's anyway because of precise and rapid injection timing coupled with the increase in fuel stroke at the injector. (The main injection is advanced so much that it acts like pilot injection at high rpms.)

So....next to find out if the pilot pulse is delivered to the injector, or not, when our own engine starts to do the old diesel clatter. I know if you had a pump coupled to an injector, and fed it a variable voltage, you could accurately measure at what minimum voltage the solenoid will react enough to lift the needle off the seat. So if normal pilot pulse voltage is say, 5v and main injection is 70v, and we got no lift or spray until 35v, then the injector is indeed faulty, as the 5v pulse from the real ecu would be ignored.
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Re: Injector noise / chatter

Post by Welly » Mon May 10, 2010 7:58 am

Good work chaps!

It would be great for someone to come up with a 'fix' for this common problem.

I've got a feeling this noise will be down to injector age/wear :(
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Re: Injector noise / chatter

Post by plod » Mon May 10, 2010 8:27 am

I just put mine down to normal diesel noise, until reading this thread, and yesterday upon driving, there was me checking where the noise and low and behold, 3.2k and it was gone.
Another one on the "to do" list I guess :( :lol: :lol:
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Re: Injector noise / chatter

Post by jasper5 » Mon May 10, 2010 9:24 am

I've been interested in this topic because my Peugeot Expert 90 HDi has this same noise.

I can confirm however that it is not related to worn injectors.....I know this because my van has had this noise from new (it was one of a large fleet of these vans I used to maintain), my van even today has only got 46,000 miles on the clock.
I have no idea what it is, but I put it down to just one of those things, nothing unusual, but annoying just the same.

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Re: Injector noise / chatter

Post by Doggy » Mon May 10, 2010 12:53 pm

Good to hear from you jasper 8)

I genuinely believe this isn't a fault - it's a feature, (no, not just tech-speak for a fault they can't fix).

My HDi 90 Xsara did it the whole time I had it, never varied. I'm convinced it just doesn't do the pre-injection thing when running at full throttle on 2 HP pump pistons and the noise you hear is just more like conventional direct injection clatter.
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Re: Injector noise / chatter

Post by omega » Mon May 10, 2010 1:20 pm

so from what ive read on here the "solution" is new injectors or get the old ones ultra sonic cleaned???

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Re: Injector noise / chatter

Post by steve_earwig » Mon May 10, 2010 1:23 pm

It's a mystery :( Depends whether it's a build up of crud or wear. Or "they all do that sir" :roll:
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Re: Injector noise / chatter

Post by lofty » Tue May 11, 2010 11:20 am

As jasper says, most of them are fairly noisy from new. I think its just another PSA HDi trait.

Saying that, have any of you driven a Nissan Xtrail DCi? You think hdi's are bad!!!! Think early Di 2.5 transit, but louder! Makes our hdi's seem like a swiss watch!
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Re: Injector noise / chatter

Post by jasper5 » Tue May 11, 2010 5:40 pm

Yeah, those Nissan Di engines are extremely noisy.The old Navara and Patrol engines are very noisy too.

One petrol engined car that used to have a similar noise was the Rover 25 model, they used to rattle like hell.The noise on those was always related to "piston slap".The old Nissan Sunny from 83 to 86 also has this rattle, as well as the Cherry (same engine), even some of the old Morris Marinas.

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Re: Injector noise / chatter

Post by FlySpeck » Sat May 15, 2010 1:39 am

I agree it sounds like conventional DI diesel clatter, and I did a wee experiment, connecting a rubber tube to each injector leakback nozzle but only to the outside as a listening device (used it like a stethoscope) and no1 injector operates with a deep "clacking" sound, while the other 3 tick softly like petrol injectors (normal sound) - of course, the injectors on the diesel operate in exact coincidence with the firing (combustion) sounds so they are impossible to discern from diesel combustion clatter while driving, but the HDi has one claim to fame, and that is reduced combustion clatter due to the pilot injection phase, where a 40ms pulse fires 1cubic mm of diesel to warm the air charge and smooth the firing "bang" when the main injection pulse happens, as the flame front begins smoothly instead of suddenly, therefore an HDi that clatters, is obviously not supposed to, and I now feel the injector is at fault - from a noisy solenoid after my stethoscope tests.

One could rig a pulsed test voltage (or just dc thats switched on and off manually) to each injector in turn, and trigger the solenoids - hearing them operate without any engine noise (while not running obv lol) so you would hear a distinctly bad injector right away.....I have to now find the voltage they operate at exactly and make a pulser (oscillator) circuit that fires the injectors for test purposes, then try each one to see if the noise is different on one or more injectors. They might dribble some fuel into the cylinders when tested but the rail should not be under high pressure, just held full and so no real fuel will be injected.

New motors that had this noise may have had bad injectors right from the off due to quality control not being what it should be at the peugeot manufacturing process.
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Re: Injector noise / chatter

Post by FlySpeck » Sat May 15, 2010 4:17 am

New tech info from a site (christiantena) now leads me down an interesting route...

The noise is as said between 2k and 3.2k rpm then abruptly stops....now this is when the 3rd piston on the HP pump comes in, and increases rail pressure to max (regulated), SO disconnecting the 3rd piston deactivation solenoid plug, would result in full pump pressure all the time instead of "restricted" pressure - I will try this and see if the noise is gone ALL the time like it does at 3200 rpm......this rpm related change is the only thing that stops me believing its an injector fault 100%.

If the 3rd piston does operate at 3200 rpm, and this results in a silent engine...then disconnecting the deactivator plug is worth a try (harmless as I am led to understand as some bosch pumps do not have this and can still be used in place of 3 piston pump with no problems). The 3rd piston deactivator is there to take some of the pump torque loading off the engine at low revs, and also if the fuel temp reaches more than 106 deg C it also operates, but unless held "off" - the 3rd piston would always operate.

If I get a CEL from taking this plug off, then I have a scanner which can clear it, so i'm happy to try the experiment as this will clear in my mind, the reason for the rpm range being so specific as to when the noise is present, and when it is not. The only reference I can find in the HDi / Bosch tech papers is that the HP pump deactivates the 3rd piston purely to reduce engine load at low revs or if the fuel is very hot - until exactly 3200 rpm....then its on again until the redline....

Interestingly, the injector on my engine that "clacks" is the last one on the rail.....and may be getting reduced pressure between 2k and 3k due to 3rd piston not operating, and since the injectors use fuel pressure to close themselves maybe being last on the rail means it isnt getting the pressure it wants to operate quietly? Its nightshift and my brain is melting from reading all those bosch docs but thats as far as I got - hope you guys see where im going with this and maybe think the same as me?
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Re: Injector noise / chatter

Post by steve_earwig » Sat May 15, 2010 7:41 am

I thought the injector rail was fed from the middle :? I seem to recall the noisiest injector on mine is the one nearest the clutch...

My eyes just glaze over with the technical stuff now, I'm also getting sick of reading the same guff over and over again (it's the crankshaft pulley :x ).
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Re: Injector noise / chatter

Post by FlySpeck » Mon May 17, 2010 12:12 am

haha i know mate.

Ok, talked to a guy who is a bench technician for Bosch and lives in France....my wifes aunty has a house there and we been over before helping deco etc.

Local mayor (also postman, cop and hotelier) has a nephew, Peter, who is the bloke concerned....I heard "he works for Bosch, is pug fan" - and bingo my ears are pinned back! I got talking to him, and it turns out thus:

The injector is at fault, Bosch dont sell parts except the nozzle (which isnt the problem) to anyone, so "recon" injectors from anywhere can be just as badly worn as they only swap the nozzle (except in Bosch themselves)....scrapyards are better, or buy second hand as cheap as poss and swap them. Or pay Bosch loadsadosh to swap it out lol.

What happens is, the pin (rod) that moves up and down to let the pressurised fuel into the nozzle orifice holes (and they are only 0.0135 mm across for the anoracks) wears in its forged steel bore....the injectors use pressure balance to stay closed, as no solenoid coil could lift the needle against such massive fuel pressure, so the injector has 2 chambers, called "pressure" and "control" - both fed rail pressure fuel, so the needle actuator stays closed. The solenoid when fired, introduces a small controlled leak to the leakback pipe from the top "control" chamber, and the huge pressure in the bottom chamber (pressure chamber) surrounding the needle end, forces the needle rod upwards due to pressure difference, and this lets the fuel to the nozzle where the rail pressure forces it through.

The ecu uses pilot or pre - injection from 2k rpm to 3.2k rpm, then turns it off. What goes wrong is the worn injector allows fuel from the pressure chamber to leak up to the control chamber and hold the solenoid valve open too long or make it shut slowly, which makes the supposed tiny (1ml) pilot injection turn into a full blown spray - which is obviously wrong in timing terms, as it forces strong pre-ignition and an early combustion bang (clatter) in the affected cylinder, and hence you are hearing the cylinder not the injector itself. It is "pinking" heavily, which to a TDI / HDI just means the timing is advanced on that one cylinder due to the leaking injector.

A leakback test then shows which injectors are not admitting full pressure to the nozzle but leaking back into the control chamber and hence out to the leakback pipe.

Simply put, its good, as it means it is only an injector, which can be had cheap from france, or get a scrappy one and swap till it shuts up. So - it is pinking - its not great to have - swap a second hand injector with each one in turn, matching the injector "class" (2,3,4 etc stamped on the head of the injector) and drive it to see if you have hit the right one - or use a screwdriver or rubber tube to listen to the plastic leakback connector above each one, the bad one will clack with a heavy sound to the ear, good ones tick softly....swap the dud out - Job Done!

**btw I experimented with the 3rd piston deactivator plug off - so full rail pressure from the pump all the time instead of graduated 200 bar to 1350 bar between 2k and 3.2k rpm....it pulls stronger at low revs (below 2k) but the rattle is slightly worse low down (as expected - higher pressure at the rail sooner so earlier leakage) - oh and the injectors fire using inductive kickback from each other to charge a capacitor bank in the injection ecu like a camera flash unit, which pulses the next injector which then charges the caps again when its field collapses, ready to fire the next injector......ach you get the idea. Thats why when one injector fails completely like having an open circuit solenoid valve - the whole lot fail and the engine stops as the chain reaction is broken that produces the high voltage pulses. unusual but clever.

TaDa!!!
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Re: Injector noise / chatter

Post by DiscoPol » Mon May 17, 2010 12:28 pm

Hats off to you sir!!

that's some good research you've done there, just need to see if I can swap the buggers now then :roll:

so still the same method of repair just a different reason. :)
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