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Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy on August 1, 2011, 3:00 pm

Year of Manufacture *: 2005 (55)
Engine Size and Code *: 2.0TDI BLB
( Optional ) Scanner Used: VCDS
( Optional) Fault Codes: P16686

After a little help from a VAG expert!

Got this A4 TDI in, complaints are a REALLY rough idle (shakes the whole car) and really bad smoking (black). Report was car running fine, then a sudden power drop accompanied by lots of black smke from the exhaust. Did a fault code scan and came up with 3 codes:

16485 Mass Air flow sensor, implausible signal
16683 boost pressure regulation: control range not reached
16686 cylinder 2 misfire detected

I traced 2 out of three codes to a broken EGR flap which has now been renewed. A smoke test of the turbo/intake system shows no leaks.I still have the rough idle and the cylinder two misfire problem. Looking at the fuelling values for the 4 injectors shows:

Cyl 1 -1.29mg/st
Cyl 2, 2.99mg/st
Cyl 3, 0.24mg/st
Cyl 4, -2.31mg/st

Number 2 and 4 seem out to me - any ideas?
I've checked the injector current on the multiplug at the rear of the head and all 4 signals look like they are present. My next step is to check the in-head injector loom.

Any advice on from the VAG collective greatly appreciated.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Philip Cockburn <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2627' width='330' height='300' border=0 style='border:none;'> on August 1, 2011, 8:56 pm, in reply to "Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Philip Cockburn

Hi Sean,
I suspect your no2 injector is faulty, check the injector solenoid status (group 18) all should be the same (0 at idle i recall) this should indicate the circuit from ECU to injector (if not then it could be the loom so carry out resistance tests although your current measuments already suggest circuit is complete).
We have replaced several of these injectors on the 1.9 for same reason, +/- 2.8mm/s is the max allowed value so anything above registers a code.
There are a couple of things to watch out for when doing the job, the injector must be fitted & tightened square to the cyl head posts (if not they can work loose & damage injector/camshaft), the bolt that holds the injector in place is a stretch bolt & should be replaced, the 1.9tdi also has another couple of bolts that hold the shaft in place that are stretch too. There is a procedure to set the clearance of the injector which is basically to allow a clearance when at max stop (largest point of camshaft lobe) so not to damage injector, where you are supposed to use a dial guage to check camshaft fully down then tighten the adjuster bolt to dead-stop then back off either 1/4 turn or 1/2 turn depending on engine. We generally buy exchange injectors from factors (Bosch) which i am assuming is what is fitted to this car, the later 2.0 TDi have siemens injectors which seem to fail electrically & stop the engine from running (giving a relay code) these do not fail in the same way that the 1.9 ones did, they do however get other issues with seals leaking inside the head & cracks in the head which cause rough running.
Hope this helps, p.s it is a good idea to replace the loom inside the head at the same time as fitting an injector £40-odd quid?
Regards, Philip

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 2, 2011, 12:57 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Thanks for the info Philip, appreciated.

I have looked at the injector status this morning and all are showing zero, however, the correction value is 'jammed' at +2.99 and does not vary like the others do.

I have taken the head loom out and checked it over and it seems to be fine. Each injector measures 0.4 ohms. I have scoped the individual injector currents and all appear to be a correct profile and drawing just over 18A peak current then modulated at around 12.5A.

Just a thought - could the twin-pump failing cause this issue i.e fuel starvation (although i'd expect all injector values to be high if this were the case?)

If it is an injector i may kick this one over to a VAG specialist as i've got enough problems already and VAG isnt my speciality!

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Philip Cockburn <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2627' width='330' height='300' border=0 style='border:none;'> on August 2, 2011, 8:08 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Philip Cockburn

Hi again Sean, as you say the tandem pump would cause issues with all injectors & so i still think its an injector, there can also be some meaningful data on group 23 (beginning of injection point or B.I.P for short, which is the digital/ECU`s way of displaying what we would measure with a scope, the knee-jerk point of the current build section of waveform, similar to the wing-type pattern on a petrol injector when the injector actually opens) basically the BIP indicates to the ECU that the solenoid valve is fully closed/or in other words when injection starts, BIP should be as near zero as possible, the spec can be +/- 90 but the further away from zero, the more likely an issue has/is starting to occur, this can seem a bit confusing at times, especially as if say there is some air in the injector, the solenoid valve will close quicker than expected, the ECU can then register a fault code such as BIP below control limit etc.
Back to your issue, it seems a shame to stop now as you have tested beyond where many would get to & from here its just good engineering practices to see the job through, if you want to talk it over i am in the office tomorrow so can easily take a call 01334 850 259.
Remember; what doesn't kill us makes us stronger!
Regards, Phil.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 3, 2011, 6:12 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Well, we have an answer, of sorts. The timing belt had jumped teeth! How i'm not sure - the car has only 74500 on the odometer although the belt is 6yrs old now, but the owner does like a 'spirited drive'.

Checking the timing this morning and cranking over by hand on the crank pulley i noticed that it didnt feel quite right. I suspect there may be valve to piston contact so may have to whip the head off to check later. This hole is getting deeper by the minute.....

Just hypothesising as to the cause, can these PD injectors fail and allow excess fuel into the cylinder possibly causing a hydraulic lock and causing the timing belt to jump or do they fail-safe i.e no injection at all? My concern is that 'just' refitting a new belt and retiming it wont be the end of the problem if an injector is leaking and it happens again?

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Alan Lange <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3293' width='330' height='300' border=0 style='border:none;'> on August 3, 2011, 8:00 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hello Sean, hydraulic lock is an interesting theory but I don't think it would make the belt jump as the crank is the driving pulley so if it locks it should just stop driving the cam. It may bend a con rod though. I would be looking for foreign objects in the cambelt area. Hope this makes sense (I think it does in my head).
Also looking at your fuel trims it looks like you have a bent no'2 inlet valve (+2.99 on no.2- ecu trying to speed that cylinder up but when it sprays, fuel is being lost into the inlet manifold as no.4 is on the inlet stroke causing that cylinder to be on -2.31). Just my theory. Hope this helps, Alan.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Kevin Apps <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2589' width='330' height='300' border=0 style='border:none;'> on August 3, 2011, 9:34 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Kevin Apps

Sean

"The timing belt had jumped teeth" and not stripped teeth off!! Think of the easyiest way a belt could possiblily jump with-out damage.
I am assuming the belt was still tensioned some-where near correct.
Kev.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 3, 2011, 10:42 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Thanks for the advice and theories guys, all appreciated.

The belt looked fairly normal and appeared to be tensioned ok with no evidence of stripped teeth from what i can see. i'll take it off tomorrow and give it a good look.

I'm not confident in the reason for this apparent belt slip as nothing so far looks obviously wrong, and dont like the feel of the engine so i'm going to discuss with customer and have the head off to be safe. Keep the ideas coming chaps!

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Alan Lange <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3293' width='330' height='300' border=0 style='border:none;'> on August 3, 2011, 11:02 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Alan Lange

It would also be worth checking the cam and valves incase something has siezed there first causing the belt to jump. In theory if one valve has hit due to incorrect valve timing (ie inlet valve), all the other inlet valves should have done the same. I have done quite a few 1.9 pd's where the cam has worn through the top of the hydraulic tappet.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Philip Cockburn <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2627' width='330' height='300' border=0 style='border:none;'> on August 4, 2011, 9:00 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi Sean, et all,
I have been busy the last couple of days & missed these extra issues.
In reply to Kevin's post you say the timing belt tension seemed ok but was it spot-on or on the loose side of right? i.e could it possibly have jumped or not? was it the O/E belt & tensioner from factory or had it been changed & possibly incorrectly timed/tensioned?
Alan could be spot-on with some sort of damage & the ECU is trying to smooth out but unable to do so within a reasonable set of limits (therefore at stop) assuming that the cam had possibly nipped up & caused the belt to jump, could you remove the caps one at a time to inspect for damage & if no damage, then what about timing it up correctly & carrying out a compression test, looking especially carefully at the first couple of compression strokes on the gauge to see what each cylinder can produce instantly rather than what it can build up to with several more compression strokes, if then in doubt a compression-loss test to identify possible issues before removing the head?
I must admit that Alan was thinking on his feet a far more than i was here, it not unusual to see another cylinder backing off fueling after a large + reading, but i guess should normally be the next cylinder in firing order so i should have thought it through a bit further, sorry.
You could always have swapped injectors around yourself to prove before buying a new one, but you must have had also other doubts if you went on to check timing first, just as well you did or i might have been recieving your invoice by now!.
Phil.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 4, 2011, 10:29 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi all,

Thanks for all the useful advice. As i was uncomfortable about the feel of the engine i took the head off (with the customers agreement) and have found some valve to-piston contact, mostly in cylinder 1, a couple of bent valves and all sorts of other nasties! The cam gear looks ok on an initial quick look but i'll be stripping that down later tomorrow for a thorough look.

Interestingly, the piston crown in cylinder 2, the one initially throwing the misfire code and the +2.99 correction, looks significantly different than the other three! Cyls 1,3 & 4 all show normal signs of combustion with a light black covering and minor amounts of carbon build up, whereas cylinder 2 piston crown looks really clean with no soot/carbon - i can still read the code numbers off the crown! I suspect there's not a lot of combustion going on in this cylinder for quite a while - either that or its had a new piston at some stage.

Cylinder 2 on the right, 3 on the left

Looks like i've inherited a nightmare. I'm still not sure what initially caused the timing to jump, and i've had so many theories run through my mind (including 1 dream!) that i'm not even sure that (a) fixing the timing issue will cure the original misfire and that (b)having not found a definitive 'fault' that caused the timing jump that can i can fix that it wont just happen again!

How do i get talked into doing VAG jobs.........

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Kevin Apps <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT2589' width='330' height='300' border=0 style='border:none;'> on August 5, 2011, 12:51 am, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Kevin Apps

Sean
Well the easyiest way from a belt to jump with-out damage to the belt is if it turns counter-clockwise ie not the normal direction (it unload,s the tensioner, Honda,s visa-versa.

But those pistons look to different to believed (or is photo not correct)
Kev.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 5, 2011, 8:26 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

The nightmare deepens - need to replace one piston so took the sump off (eventually - who designed this damn engine....) to find the oil pan full of what's left of the oil pump chain tensioner (bits of broken steel spring & plastic foot)! The chain looks damaged also, like its been squashed / pinched!

Interestingly undoing the bolts that hold the balance shaft assembly to the bottom of the crankcase i noted uneven torques required to loosen - i swear someone has been in this engine beforehand.....

Anyone recommend somewhere i can get a decent reconditioned complete engine? Scoured a few internet sites but they all look a bit 'iffy' and i'm not sure i'll be getting any better than i've already got!

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by John Fletcher <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT5112' width='330' height='300' border=0 style='border:none;'> on August 6, 2011, 10:25 am, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
John Fletcher

Hi SEAN
I am in the middle of changing one of these engines I could,nt find one anywhere the customer found one it was supposed to be out of an 08 vehicle we have had to change everything over including swapping sumps and having to modify the oil pick up it has turned out to be a nightmare . regarding your engine I would,nt try to repair it the oil pump alone is over £1100 I have a v/w guy he has changed one and said he would never do another .

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 6, 2011, 11:41 am, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

I found a company that does a repair kit for the oil pump chain drive - may be useful for others as this seems to be a fairly common issue.

www.powermaxengineering.com

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Jon Morgan <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3190' width='330' height='300' border=0 style='border:none;'> on August 6, 2011, 4:55 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi Sean,
the photo of the pistons as Kevin pointed out - looks as though the pistons are different.
1 x flat top & one with a swirl recess.

Or is it a trick of the light??

The correct pistons have valve & swirl recesses off memory.

I haven't had the misfortune to attempt an oil pump on one of these yet, but it may be worth perusing the link below - as they seem to be a tad nasty.

http://members.boardhost.com/ukautotalk8/msg/1239346267.html

As Peter Sokolowski point out in the last post, the turbo's are prone to failure after oil pump failure.

See here -

http://members.boardhost.com/ukautotalk8/msg/1307635395.html

Looking like a can stuffed full of worms from where I sit??

hth,

Jon.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 6, 2011, 6:08 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi all,

The pistons are the same shape, its just bad light. The lack of carbon on #2 makes it look all pointed compared to the other two which are flat-matt black with soot.

The oil pump hadn't actually failed on this one, but it looks as though it was very close to doing so. I want to renew the chain drive and tensioner/sprockets to prevent any further issues with this area for a while. I'd quite like to install a full recon engine as this customers bill is starting to look like a lottery win and Lord knows what other nasties are lurking in this engine. However, i cant find a decent one - some sites are quoting as little as £1600 but with the cylinder head at ~700 and the oil pump at £1000+ alone i'm not sure what they have replaced for that price!

One for the PD-experts - on the injectors there is a shiny metal sleeve between the two o-rings with a hole in it (for the fuel supply). Is this meant to be fixed or is it OK to be able to rotate? On the one i've taken out (the suspected duff injector #2) this sleeve is free to spin around - i'm wondering it this is meant to be held in alignment with the fuel ports in the head/fuel rail so that fuel can flow into the injector (like the position in the first photo)? Its also got signs of wear on one side so i'm wondering if Audi have at some stage changed this injector and installed it poorly and blocked the fuel supply to the injector by allowing this sleeve to be in the wrong place and hence blocking fuel flow to the injector port? I could be miles off, i'm no PD expert so if someone could tell me if thats normal or not it would help!

It'll be a cold day in hell before i sell my BMW and move to a VAG thats for sure! I wish i hadnt taken this job on..........

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by phil kingdon <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1433' width='330' height='300' border=0 style='border:none;'> on August 7, 2011, 5:28 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Phil Kingdon

Hi Sean,
That wear on the injector will allow oil dilution, the head will be worn too!
I think if you buy a recon engine for this you will find that the injector port in the head will have been sleeved, thats how to do it cheaply. Those injectors must wobble to cause this wear, does the 2 litre have only one bolt as the 1.9?
Cheers Phrom fill.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 7, 2011, 6:27 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi Phil,

No mate, its got 2 bolts holding the injector down.

Customer is getting me to rebuild the engine with a recon head, new oil pump chain drive, piston, cambelt & water pump and a new injector. Oh joy, as if i didnt have enough to do already.....

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Andy Evans <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT5518' width='330' height='300' border=0 style='border:none;'> on August 7, 2011, 7:30 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi Sean
out of interest how much is an engine from the dealers?

cheers Andy E

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Mark Carter <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1428' width='330' height='300' border=0 style='border:none;'> on August 7, 2011, 8:13 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Hi Sean,

Just a small note about the Injectors, the section you called the fuel inlet is in fact the outlet.

Look very carefully at the top photo and further down the injector body and you will see lots of tiny holes (they are 5 microns), this is the fuel inlet, do not handle the injector here as just the dead skin off your hands can block the filter.

I understand that this may be the least of your troubles at the moment but the last thing you need is to kill a couple of injectors into the bargain.

Regards Mark

Modern cars, Its all wizardry and witchcraft

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Sean Murphy <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT1788' width='330' height='300' border=0 style='border:none;'> on August 7, 2011, 8:56 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Thanks for the advice guys - as i'm no VAG expert i welcome and take on board all comments!

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Jon Morgan <iframe src='https://members.boardhost.com/ukautotalk8/info/user=ukat3190' width='330' height='300' border=0 style='border:none;'> on August 8, 2011, 1:36 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"
Jonathan Morgan

Andy,
A short motor off VAG is just shy of £6000 + VAT

An exchange short motor off VAG is £3100 + VAT

Jon.

Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #

Posted by Andy Evans <iframe src='https://members.boardhost.com/ukautotalk8/info/user=UKAT5518' width='330' height='300' border=0 style='border:none;'> on August 8, 2011, 1:38 pm, in reply to "Re: Audi A4 2.0TDi 140 BLB - Rough idle, code P16686 #"

Thanks for that Jon,
I think I know which one I would be choosing.

Andy E

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