I'll try to be concise.

 

Car:

06 1.9 PD105 BKC

 

Problem:

Goes into limp mode(no MIL) when driven hard, becoming more frequent, cycling ignition clears limp.  Doing this repeatedly shows MIL and maxidot displays 'Workshop Emissions!' requiring DTC 16618 - Charge pressure control; Regulating limit surpassed-Permanent to be cleared.  Odd extended groaning sound on engine switch off.

 

Action taken:

Vacuum hoses checked-ok.

Vacuum solenoid block checked, some ports showed signs of fine rust buildup-washed out thoroughly with IPA and dried gently with compressed air.  

MAF+MAP sensors clean-washed anyway with IPA.

Turbo Actuator, free to move full travel and operates correctly with vacuum-sprayed with GT85 (turbo treated to Mr Muscle since I was under the car)

 

Result:

Engine pulls slightly better but still exhibits the initial limp problem, however less frequently.  Odd sound gone, replaced by meaningful click with ignition on/off.

 

My thoughts:

As I can't find any mechanical fault, it has to be electrical.  Rather than replace the MAF+MAP sensors at this initial stage, I plan to investigate the vacuum solenoid block further given it had rust deposits which could indicate sticky internal valve(s).  The box looks like it might open fully to access the workings...  My theory being that a slow moving valve isn't releasing the turbo actuator quickly enough/fully to prevent an overboost condition from occurring.

 

More inspection and testing required.

 

Your thoughts:

Which sensor is most likely faulty/can they be tested or is it a case of replacing parts until fixed?

 

Any meaningful input?

8 minutes ago, MicMac said:

Which sensor is most likely faulty/can they be tested

Ever hear of VCDS?

Yes, however I only have Delphi with a Chinesium DS150E.

I've taken the vacuum solenoid valve block apart pn 6Q0906625

 

Does the phrase 'no user serviceable parts inside' come to mind... Shouldn't stop you having a look though!

 

The top large cover really doesn't offer any useful access.  It is the smaller cover on the other side which at least allows access to the vacuum channels.  There's a rusty brown circular rubber diaphragm I believe causes the odd groaning/cow moo sound.

 

After previous cleaning there is obviously still rust residue so I'm going to give it a better internal clean/lube and possibly test the solenoids electrically.

 

I suspect moisture ingress which caused the rusty valve(s) was from old faults:

1-leaking vacuum nipple on the tandem pump, wobbly and fixed.

2-split rigid plastic vacuum pipe to brake master cylinder, section removed/sleeved.

 

I'll let you know how it goes after I've cleaned and reassembled the unit.

 

For reference these are the affected ports:

P1 Vacuum line from tandem pump

P5 Vacuum reservoir

P6 Turbo actuator

 

These links may be helpful:

Edited 6 January, 20206 yr by MicMac
Added photos

At least I know where the moo cow noise comes from, I describe it as a bovine terminal breath!

24 minutes ago, J.R. said:

At least I know where the moo cow noise comes from, I describe it as a bovine terminal breath!

 

Hahaha yes, the cow killing scene from the film 'Me, myself and Irene' springs to mind.

 

 

Edited 6 January, 20206 yr by MicMac
Added link

UPDATE

 

I cleaned and glued the vacuum solenoid block back together and noticed limp mode was less frequent.

 

Thinking there was irreparable internal rust damage I then replaced the unit with a used item, not much change in provoking limp mode.

 

FYI pins 1 & 2 are 30 ohms and 3 & 5/4 & 6 are 15 ohms.  Destructive investigation of the old unit shows no serviceable internals, the solenoids are sealed with rubber boots so cannot rust although the valves themselves could be fouled in extreme cases. I'll be checking hoses 1, 5 and 6 when the weather is better to find the source of the rust.

 

I also replaced the MAF sensor, again with a used item, like for like a genuine Bosch item. I gave it a good ultrasonic clean in IPA before fitting and so far I've not had any problems.

 

It is interesting to note that during scanning I found all 4 glow plugs had logged a permanent fault and sure enough each one showed >1K ohm resistance so were shot.  Who knows how long this has been the case as I've only recently bought an OBD scanner.

 

In any case it always starts without issue so I now save a few seconds waiting for the GP lamp to extinguish before turning the key and will leave as is until it becomes a problem, my concern is carbon build up on the cold plugs causing removal difficulties if/when I need to replace them.

Booting it triggers limp mode again so whatever improved was only temporary.

 

I've cleaned/checked the bit in the middle (turbo), replaced the bit upstream (MAF) so that only leaves the bit downstream (MAP).

 

I'll fit another next week and let you all know how it goes.

Sounds similar to mine 2.0tdi checked and cleaned everything but in the end replaced the turbo wish I’d started with that. 

Replacing the turbo isn't currently an option.

 

Before I buy another MAP sensor I' m going to remove and inspect all pipework downwind of the turbo again.

 

Reading a few posts about similar VW experiences seems to indicate an easy to miss split in a flexible elbow hose was the root of the problem, what's the chances it's that simple...

 

Anyway I just need a break in the weather before crawling around under the car.

 

I don't know what it's like for non sports suspension versions. With limited ground clearance I have to place a brick in front of the drive wheels, drive onto them so I have enough clearance for the trolley jack, jack up enough to get one axle stand in place, do the same for the other side, back to the first side with a wooden block on the jack so I can reach the next stop on the axle stand, back to the other side and repeat before checking for stability.  I could perhaps omit a step but that usually creates too much lift on one side and a teetering axle stand, way too dodgy.

 

I'm knacked before I start the job!

Pipework double checked, MAP sensor replaced... no change.

 

I know the VNT mechanism moves freely from stop to stop so my next idea is to fix a borescope somehow for a view of the actuator whilst driving.

 

Triggering limp mode is easily done and I'll be able to review video to ascertain what position things were in when triggered.

 

I figure if the actuator is fully in the low boost position the fault is electrical in nature as it rules out the mechanical side of things.

 

If it's anywhere else I'm thinking wiring breaks/corroded connections/tired actuator return spring.

 

Interesting to note that real time diagnostic values change with engine speed as you may expect however the MAF  value just sits at 0.0-0.1 g/s.  Could it just be a broken data wire to the MAF sensor that's causing the overboost limp mode?

You maf value is bad, I’d start there, unplug your maf and see if it stops limp mode, but that value is miles off and basically a dead reading, so it needs fixing, it could be the cause of your limp mode yes.

 

i have cars in the air all the time and I find a set of caravan levelling ramps best, drive onto the ramps, I’ll then jack up from there.

 

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F272339753140
 

that’s what I use, light easy to store and is high enough to get under tray off, if I’m doing a big job I’ll drive onto these, under tray off and the jack up on the subframe if it’s man enough and then stands under each side in one go 👍

 

 

Just invest in VCDS, it would have paid for itself by now with the amount of faffing about and parts changing you have done

 

How many miles are on it? I wonder if there is some hysteresis in the vane linkage inside, that would make it hard to control boost.

 

have you checked the integrity of the diaphragm in the actuator?

 

 

Edited 9 February, 20206 yr by SuperbTWM

@Vrsburnzy

 

Interesting ramps, never gave them a second thought when old angle iron items were unable to clear bodywork.  Food for thanks for the heads up.

 

@SuperbTWM

 

As the song goes 'money's too tight to mention'!

Having recently found wiring details I was able to check both MAF/MAP sensors, the MAF output read 5v permanently so I replaced it for the original item, which apparently works D-0H!

 

Both sensors output the book values more or less and I still get overboost-induced limp mode, even with the MAF unplugged it's the same but with added MAF signal-low DTC.

 

Any words of wisdom?

 

I'd try disconnecting the VNT actuator vacuum but I'm pretty sure I tried that a while back and apart from many engine stalls I got an underboost limp mode before I could try for an overboost error at speed.

 

More testing as weather permits, I know the vacuum solenoid block+VNT actuator both function, maybe I can check the voltages to the VSB.

 

On 09/02/2020 at 12:03, SuperbTWM said:

have you checked the integrity of the diaphragm in the actuator?

 

 

 

have you proved this? if you get a vac pump and locally move the actuator while watching it you can verify the actuator is moving full travel, not sticking and that the diaphragm is good.

Edited 3 March, 20206 yr by SuperbTWM

Yes, the actuator works fine from stop to stop.

 

Tested by removing/replacing vac pipe on actuator with engine running, using actuator activation via diagnostics and by hand with a 50ml syringe and length of pipe.

Have you checked how much boost its making with an actual gauge?

No, I don't have specialised gear.

 

I could probably cobble something together but whether it gave an accurate measurement is another thing.

I think I've got it sorted.

 

The turbo actuator spring was a bit weak returning to the low boost position, leaving it approximately 5mm short of fully pegged, that's a lot when full travel is probably 20mm.

 

Adjusted the rod nuts to just peg it plus half a turn for good measure.

 

Initial tests are good with it only going into limp mode (no EML) when foot to the floor and autoban speeds are reached.  Diagnostics show the usual overboost code (remap related).

 

I was going to remove the actuator for inspection but the 2 retaining bolts will need a torch to loosen them.  Unless the turbo plays up again I'll leave it as is having just taken 14 years of spring settle out of the equation. Essentially I've just made a worn part function longer, If it does play up I'll replace the actuator.

 

Thanks for all the helpful input... I can overtake again!

Cough!! 🤣

 

 

To conclude:

 

I wasn't happy with limp mode still happening at high speed so bought a new actuator for £9.99 + vacuum pump tester £10.99 on ebay.

 

Both items are made in China, cheap but perfectly useable.

 

Set to touch stop screw at 18 inHg and works perfectly.

 

Out of curiosity I cut the old actuator open to find the internal spring, despite being substantial, was in 2 rusty pieces with no corrosion to the inner shell.  I can only deduce that the previous long-term vacuum leak at the tandem pump allowed a minute amount of atmospheric moisture ingress over time and the spring steel was particularly rust prone.

 

Incidentally there is now a marked increase in displayed fuel economy.  MPG now plus 5-10.