Limp mode tdi cured!

[ScottyP45]

I eventually decided the map sensor in the car was to blame in my case, and took the pipe off that leads from the intake to the ecu, and it was clogged with crap! I couldnt clear it so I replaced it with a silicon tube and flushed the map out with wd40 (only thing i had) and so far, no boost cut or limp mode!

It usually dies at a fair tilt uphill in 4th, at the same spot every day.....tonight it never broke stride all the way home and no codes, unlike usual 000575 etc.

Woot! It could have been many things, like vac leaks, n75 bad, vnt sticking, intake sooted, egr passing, and sooted up exhaust turbine. I tested everything one by one that I could, and when I found oil in the map tube, I knew from working on industrial instruments that causes bad readings on any pressure device. Hopefully thats it, but anyone having tdi boost or limp problems, gimme a shout, I learned a lot this week

 

[fARQUARE]

Sounds like you've been going through the same process as me since buying the tdi. Your engine is the afn? The map sensor is in the ecu, there is a 3 inch length of hose inside the ecu that you should replece too if you have not done so. When I changed mine there was a lot of oil in the vac lines, I blew as much as I could out of the hard lines and replaced all the other hoses with braided hose from gsf, cost about 5 quid and was well worth it.
In the end I replaced my maf and my n75, I suspect the maf was good but it was a good starting point.
I ended up buying a vac pump and a vagcom lead to narrow down some of the problems, if you're near glasgow your more than welcome to borrow it to test the actuator on the turbo and the flap in the n18.
I now dont get the 00575 which is good but I do get a 01265 code which wasnt there before, i'm kind of stumped on this one but it's not affecting performance as far as I can tell.

I also sent the ecu away to get re-mapped which I was pretty happy with, I can give you details of who I used if you're interested.

 

[ScottyP45]

cheers FarQ, thats very kind of you mate.

I have capped off the EGR valve and blanked the vac line to it, that cured the dead-spot at 2k rpm, and will keep it running sweet and clean.

The actuators work I think, but I'll strip the turbo and intake when im on holiday from work and I'm plumbing a pressure gauge in today to measure boost. I replaced the entire ecu boost line from MAP to intake with a single length of silicon clear vac tube, and I can see oily crud creeping up the start of the pipe from the intake already so the whole intake and cooler need cleaned out when I get the chance, but my Legacy GT TT is still in the garage getting the 2nd turbo up-pipe welded so when thats fixed, I can use it and strip the B5 intake down to clean it out properly.

Your EGR solenoid may be faulty hence the 01265 code.....incidentally its exactly the same part as the N75 so can be swapped over with the N18 and works exactly the same.

I may use compressed air from a tyre inflator wi the airbed adaptor cone, to clear the hardlines out, but yeah all the vac pipes will be replaced as soon as month end comes (pay day woot) - I live in Fife so not too far away from your self, I have vagcom but my lead is ********, saying that they are cheapo from ebay. (non genuine ones of course but still work if you buy the right one .)

It has crossed my mind to get a tuning box, as the car really doesnt warrant an expensive remap, its just an old workhorse. If my B6 was a TDi I would definately get that done but as the engine is ****** I may buy some toys for the B5 with the money from when I break the B6 up.

 

[fARQUARE]

it's not clear from your reply but there is an additional wee bit of hose inside the ecu too as well as the hard line going from the inlet pipe to the ecu, only 4 torx bolts to get the ecu open, worth doing if you havent done already.

Interesting that you can see oil flowing up the pipe again, i would have thought that the pipe would be under vacuum as its going to the engine but i guess that diesel engines need a secondary vacuum pump so i guess the pipe being under pressure makes sense.....

from what i've read the best way to get rid of the oily vapour in the inlet tract is to put a catch can on the ccv, i think i might do this - or i guess you could also vent to atmos.... The egr in theory shoud just be hot exaust gas and particulate, it's when the EG and the ccv vapour mix that you get all the problems in the inlet....

i cleaned out my inlet maniold, quite easy to take apart due to the way the engine sits so there is plenty of room to get in with allen bolts and a big wrench. i cleaned the manifold out with a bucket of paraffin, a long screwdriver and a high power hose. When i put it all back together (even with no turbo as the n75 was duff) the car was markedly diferent and would get into 3 figs given a big straight..... i also got a new inlet gasket, but if doing again i wouldn't bother as its a thin metal gasket and in my eyes re-useable.

in terms of the re-map, i was in the same frame of mind as you. i bought this car to commute between gla and perth daily so it needs to be cheap and reliable. i used a place called more bhp, they need to put new eprom chips in th ecu due to the age of the car, it cost just shy of £160 which i think is pretty good i fully expect the usual long line of the "i would only ever get a bespoke re-map" brigade, which i can understand but not on this car, the feedback for this company seem good and i'm happy with the results. I also bought the bits and pieces to do the "evry mod" (i've seen your name on club tdi) have a search on there, cost about £3, so i'll fit this and use sparingly.

Only fial thing which might be of use is i'm also running it on bio diesel (re-cycled chip fat which is abundant in glasgow!), put about 4 tanks through in the last few months, its 89p p/l so less than £50 for a full tank and the mrs is still getting 600 miles to a tank even with 50/50 city driving. I'm expecting this to increase when i start racking up the motorway miles on the daily commute.

had a play about with the n18 tonight, swapped for the old n75 still no vacuum to the actuator, i suspect a wiring poblem - any ideas where the fuse for the n18 is?

 

[aragorn]

On the contrary, a bespoke remap is quite often nothing more than a big con. VERY few places have the knowledge and equipment to do so, and more often than not it'll be an off the shelf flash, with if your lucky some tweaks that end up in the right places.

Are you properly making your own biodiesel, or just chucking in filtered WVO?

 

[fARQUARE]

im using a place in glasgow called apple fuels, i dont have the time, space or knowledge to make my own. Best bit is you sit in the car and they fill it up for you - just like the old days! seems to be a serious operation they have, i understand they also do consultancy and you can buy home kits from them.

map seems good, chap seemed pleasant and knowelagable on the phone, ecu was sent on the tuesday (royal mail recorded) and i had it back on the thursday which was a good bit quicker than my last 1.8t sport ecu which went to custom code via courier.....

 

[ScottyP45]

Farq, yeah I replaced the entire hose to the stub on the outside of the ecu but have opened it before and theres a wee pipe inside leading to the map wi 2 steel clips eh, I blew that out before i fitted the silicon but im gonna replace all the small bore tubes and vac lines etc.

The fuse for the N18 is the same as for the MAF, N75 etc etc so they would fail also, but its the lower rhs fuse inside the ecu compartment, 15A red. Theres a beige 25A along from it and the rest are huge 80A for the GP harness etc.

btw the diesel intake is at atmosphere or boost, never vacuum as the diesel has no throttle plate, its wide open at all times. Acceleration is achieved by increasing fuel pressure and duty. The vac side from the pump is seperate entirely and not connected to the intake / boost side of the engine in a tdi. The pipe leading to the map in the ecu is only ever under boost, so the map sensor casing must be leaking a tiny amount of air, or the pipe inside, so oil is creeping up the pipe - prob coming from the cooler. It will need cleaned out along with all the intake as the original engine spilt its guts so the current one is a recon unit thats now done only 80k, tho the cars done over 200k lol (was a taxi)

I have every receipt going back to the purchase of the car inc the recon motor, so at least I know the engine is a good un.

incidentally the fuse we mentioned feeds a red/white wire that comes out of the ecu box and goes left (from the front) with only a few other wires, inside a plastic tube towards the maf first, runs on its own across the firewall to the inner wing then to the MAF. Thats the feed to the sensors, 6 of them. You can do a continuity check or voltage to ground (ignition on for vcheck) between the red/white wire and earth, should be 12v with ignition on. Each sensor that uses the same feed will also buzz to each other on continuity test with a meter, power off this time. Same result.

Here is the wiring of that circuit and fuse, have arrowed and marked the fuse in blue and the circuit fed by it in red.

Direct link to large version (balls....****** photobucket are now resizing all uploads grrrrrr)

 

[fARQUARE]

Cheers for the wiring diagram, unfortunately wiring terrifies me - anything more than checking voltage and i'm out of my depth.
I think I see what the issue is tho, there are about 4-5 wires (running from the maf to the firewall) which have been soldered together and wrapped with masking tape. I reckoned this would have been a splice for some awful tuning box in the past, I need to get a soldering bolt and properly re join and insulate those wires, looks like im loosing continuity between the maf and the n18 somewhere.

That should solve the 31-10 error im getting for 01265...
I'll run the wiring diagram past someone who knows their stuff just for piece of mind.

In terms of oil in the map pipe, I guess it could be 3 things,
1) oil in the cooler as a result of previous engine accident
2) oil in intake from ccv and egr
3) turbo seals on the intake side going

Sounds like we're in similar situations regarding our tdi's. I bought mine with almost identical engine troubles and its now running sweet. I'd say it's obviously slower point to point then my re-mapped 1.8t avant I had before, but ouce you're up and running the diesel is plenty pokey enough for overtaking and is evenly matched for in gear acceleration. That and the bonus of getting 200 more miles per tank.....

 

[ScottyP45]

there are about 4-5 wires (running from the maf to the firewall) which have been soldered together and wrapped with masking tape

Thats exactly the bit of harness im talking about mate, mine is slightly damaged there too, thats what blew that fuse S102 on mine and you get no boost at all. The red an white wire there feeds all the sensors in red on the diagram. G70 N18 N75 N108 and the brake pedal sensor etc.

I filled up on diesel at tesco, 1.10 a litre / £76 and got 680 miles from warning light to warning light and that was giving it some too but is 3/4 motorway miles and 1/4 back roads and town driving. I worked that out to be getting 44.7 mpg average, or 10 miles to a litre.

 

[fARQUARE]

Been looking at that wiring diagram for 20 mins or so and i think it's starting to make a bit of sense to me, hopefully i can get a shot at the wiring tomorow if i can get in the father in laws garage for an hour at night.

£76 to fill the tank, must have been running on fumes, i though the tank was 60l? I filled mine yesterday and i took about 56l which was £50 and that was the light just coming on. Should see 600 miles on that however i sat in traffic for 40 mins today then gunned it for 10 mins to get the road rage out of my system.

next on the list is lowering as i'm having a hard time coping with the standard tdi ride height. I've came to the conclusion that i'm not doing it myself so it will be going to my trusted mechanic to fit for about £200.
Now i need to decide what lowering kit to get, i reckon i could go 60mm lower and still be at a sensible height.

ebay shows me either springs alone £100 ish
springs and shocks from germany £170
cheapy coils £200 ish

any thoughts on the above?

 

[ScottyP45]

aye I think they look like theyre on stilts too especially after the sport as its lowered a bit. I thought about jom coilovers cos they are compact and easier to fit than full struts and springs etc but if your gonna do springs youd need say bilstein units or something as well, cos the stock shocks are crap on lowered springs.

I looked at the receipt, (seems it was about to collapse from lack of fuel indeed), put 59.55 litres in and was £66, not £76 lol and that means around 51 mpg an I have a lead foot when going to work...w00t w00t lol

Incidentally I stuck a boost gauge on T'd into the MAP pipe (well a calibrated pressure gauge from work) and it starts to get 0.1 - 0.2 bar from almost 2k then builds to 0.5 bar by 3k but never rises above that afterwards....is this low? Anyone? I would expect about 12psi maybe 14, not 7 max.....

 

[aragorn]

I'd have expected over a bar tbh. 14-18psi or so.

It should also be building much quicker than that, full boost should be available by 2k if not before, thats what the VGT is for!

 

[ScottyP45]

I thought that too mate, nice one. I guess theres still a prob then either coked up turbo, poor actuator, vac leak, bad N75 or boost leak.

There is a distinct whooshing sound under boost but thought that was normal never having had a vnt tdi before. The 0.5 bar is rock steady too, no pulsing cept slightly at idle and no spiking, just builds slowly. I think that may rule out a boost side leak but not convinced yet. Still get the occasional limp mode (only twice) but at least I know its not overboosting. Maybe the cooler is full of oil too but wouldnt think that would affect boost, just power from reduced cooling of the charge air.

??

 

[fARQUARE]

there is a test procedure on club tdi for testing the actuators, from memory the vnt actuator should start moving about 7 hg and be at full opening by 20 hg it should also stay there. I bought a cheapy vac guage of ebay to test all the hard lines before ripping them all out. I also replaced all the vac lines with hose from GSF, i think i bought 1m of 3mm ID and 1m of 5mm id and that done the trick.

Try putting the vac lin straight from the servo and the vac pump to the vnt actuator and it should shoot straight to its full throw, this is un regulated vacuum and puts my guage of the scale, you should be able to see clearly the mechanism working and whether it is sticking....

Regarding the pressure, i think yours does seem pretty low, from memory the stock pressure is 12psi mine now reads higher than that due to the re-map. One thing that would help would be to get the vagcom lead hooked up.
Something i noticed when i was going through the wars with limp mode is that there seems to be an inter-dependancy between the n75, n18 and the maf - what i mean is that when my n75 was duff my maf figures were low (even tho the maf was brand new), when i plugged in the new n75 the maf figs seemed to correct themselves.

A strange quirk of my maf figures though is that up untill a certain rpm, the actual figure is always higher than the requested, the actual rarely drops below 500 at idle and will hold 900+ at WOT. I'm not sure if this is correct but i'm sure i read somewhere about the adaptation setting for the egr valve can ake a change to these figures.

Fixed the 01265 also tonight, checked the butchered wires which turned out to be alright in the end - the loom just needed tidied up. The real issue was at the wiring plug for the N18, the ground wire that completes the circuit and cycles the solenoid had snapped most likely as a result of being un-pluged and plugged in by me to narrow down all my problems. Re-soldered & done a scan and bingo, all codes clear.

While messing about with all the pipework i had a small thought - we both have had oil in the map line to the ECU, the feed from the intake pipe is at the bottom of the pipe (6 o'clock) so if you blew out all the lines of oil and re-attached with the intake pipe nipple cocked at an angle (say 4 or 5 o'clock) then i cant see how oil would enter the pipe - i assume the current situation is gravity initially then pressure to force it up the vac pipe when the turbo spools.

 

[fARQUARE]

just another thought, i can hear my turbo but it's not as noticable as some of the new diesels i've driven (or perhaps the afn engine is just noiser!) so perhaps you have a boost leak....

i would imagine any boost leak would be accompanied by a good bit of smoke under throttle

 

[ScottyP45]

excellent points mate, I agree the oil will collect on the bottom of the boost pipe and run down the tube, getting squeezed by boost pressure. Thats a superb simple idea about rotating the boostpipe to put the nipple above the water-line so to speak.

Is your maf behaviour now (higher than req) maybe a part of your remap?

I would like to be able to switch between unreg vac direct to the vnt and normal N75 pulsed vac, just to see if the boost shoots up in reality to prove the vnt can reach its full stroke, its kinda hard to see the actuator rod on mine. And the N75 is down by all the muck of the day youd think they would mount it higher up, I may move mine when I get the new vac hosing from Samco next week.

I hear the light whistle as the turbo spools, but when opened up on boost in gear it quickly builds a shhhhhhhhhhhh sound just like air rushing thru a gap, but I assumed it was a quirk of the vnt turbo, as my 1.8T has the turbo so close to the intake you can hear it sucking when its on boost with the cone filter on, and I forgot the tdi has a standard airbox so probly shouldnt be whooshing haha.....boost leak hunting here we come.

Heres a wee return tip I been thinking about.....get a half decent digi tyre pressure gauge, small, neat and under a tenner easy, then hook up a schrader valve to it and a pipe from the valve end to your boost nipple.....you see where im going.....you have a small, cheap digi boost gauge that reads bar or psi, and could be mounted very discreetly. They will be accurate as hell too as this kind of pressure sensor is old technology now and mature...specially if you buy the RAC one out of halfrauds or summat, they are 7.99 or something last time I saw and must be decent accuracy to + or - 0.5 psi at least.

Could be powered by the battery as original as they switch themselves off, or could be easily adapted to a cig lighter power connector that takes 12v and changes it to 1.5v, 3v etc etc or even this device wired into the ignition 12v like the radio then it powers the gauge, so it comes on when you start the car. Heck you could even solder an LED in it, but the better ones have a backlight lol

Im getting a new vcds lead, the scantool is great for quick diagnosis at the roadside but cant beat vag for fiddling with stuff and logging. Need a new bat for the ****** laptop tho as it lasts 60 secs off mains....may see if theres a 12v power adaptor for it so I can run it on the car power...

 

[fARQUARE]

the maf figures were higher than requested before the re-map was done. there seems to be no side effect of this, just looks a bit strange when looking at the measuring blocks.

will have a play about this weekend to get the map pipe above the "watermark" as you mentioned, I'll also blow out the pipe again to shift any residue that's came back over the last 6 weeks. I just connect up a bike track pump to a spare length of hose to shift any oil/crap out.

if you're cleaning out your i/c anyway its easy to clean and ispect all the boost hoses for cracks or rips, this should help you track down a boost leak if you have one....

 

[ScottyP45]

i think the main leak was the tubing i used.......it was 4mm id and should be 3mm most areas, including that map pipe. I frigged smaller ends using a good section of oem rubber tube and plastic tube as link pieces, and its now sealed. There may be other leaks that ive not found but the noise has all but gone now.

Boost rises to 0.4 bar from 1500 to 1800 then lifts smartly to 0.5 bar as 2k is reached, then if the throttle is dug in 3rd at 2k, it will peak and hold 0.7 bar but boost is instant now, albeit a tad low. Ideally i would like to see a bar, but the fuel leak at the pump will be dropping pressure to one or more injectors, hence no smoke and as fuel pressure is lower, less boost from the vnt.

I havent ruled out actuator jamming, as a stab of throttle will produce 0.7 bar but gentler opening even briskly will usually only hit 0.5 bar with no spikes, no overboost, nothing. Thats what makes me think the actuator or N75 are still faulty, but further fiddling over the next week will confirm it. SO far, even pushing it from low revs in high gear, no limp mode. fingers crossed...

tried the wot test at 1500 rpm, no drama, no boost spike, no smoke.....just lifted to the usual boost and pulled smoothly. Still feel its low but want to get the leak fixed before proceeding any further, as the lower boost may be a symptom of lower injection pressure. A vnt is always spooled, even at idle it makes 0.1 to 0.2 bar and should get to full boost just after 2k, limiting to 6psi before 2k to prevent turbo damage.

I used the HKS boost gauge off the scooby as its deadly accurate as tested against a calibrated instrument and it was spot on. Its ghetto fixed using tape, to the steering column, but I put a "Y" piece in the ecu line in the black compartment, and ran the tube down thru the base of the ecu case into the interior. That way, the route was simple and the gauge is near the map, so they see the exact same thing.

A fault that affects the map pressure, will affect the gauge, so now the testing can begin, im replacing all lines with samco in a few days and will change the N75 for the N18 or pick up a valve from a breaker to test with after cleaning and testing the valve itself.

May try raw vac on the vnt actuator to prove it can go full stroke.....now i have a gauge to see what it does. If it hits 30 psi or something stupid, it'll be short duration then off the pedal, don't want to lift the head!

 

[martinA4passat]

My mate had this problem with his Passat tdi (same engine) and changed every part on the system including N75, had the VNT cleaned and still not cured, Sent the turbo off and had it re-conditioned and problem solved.The company said the VNT was the problem.

 

[tdia4]

Noticed you had bypassed your EGR valve, could you shed some light on how you did it please? I had it done on my old Bora but i bought a proper kit for it which was £55.

So the way you have done it does the egr valve not actually get removed?

Im guessing you take off the metal pipe that leads from the egr to the inlet and cover the inlet with one of these EGR Blanking Plate VW / Audi engines on eBay (end time 27-Sep-10 21:30:54 BST)

Then is it just a case of removeing the tube from the top of the egr and blocking it up with something? Tell me if i'm way off lol.

 

[ScottyP45]

no your spot on mate, I pulled the egr valve off, 4 socket bolts (allen heads) and cleaned the mushroom head to make sure it was sealed shut, made a plate of aluminium the shape of the valve flange and put it between the egr and the inlet, so the exhaust cant get past the valve head but if it did, the ally plate is there as another barrier. Also just pull the vac line off the egr and plug it with a bolt or ball bearing, then tie wrap it to the firewall hardlines to keep it out of the way, bingo no egr, cost nothing lol.

Having no vac pipe on the egr will not throw a cel, but leave the N18 plugged into the harness. Im gonna clean the inlet out and strip the turbo when I get my scooby back at the weekend, so if it takes a couple of days to finish, I still have transport!


I had a flat spot at 2k revs with the egr working, disabling it cured that right away, obviously as the egr opens it robs the turbo of exhaust pressure to make boost.

 

[tdia4]

Ok cheers, so i'll need 2 of them blanking plates then? One that will blank the hole that comes directly off the egr to the top of the inlet? and one for where the metal pipe leads to the bottom of the inlet?

 

[ScottyP45]

Remove the rubber tube arrowed in yellow, and insert a blanking plate in the area arrowed in red, thats the egr to inlet connection, the other end is exhaust manifold and blocked by closed egr valve now no vacuum is available...

Update, I have now replaced my boost tubing from inlet to ecu and internal to the ecu, with high pressure 3mm silicon, still getting limp mode up hills in 4th, now to replace all the vac lines too. Boost now sharper to come on, and holds 0.6 but thats still low at high load.

 

[aragorn]

Turbo Vanes sticking?

 

[tdia4]

Cheers for the pic matey.

You had all your undertray off to check the intercooler pipes? Had mine off yesterday to do a oil change and all of the clips holding the pipes on were quite loose so i tightened them all up while there.

 

[ScottyP45]

Aragorn, could be mate. Gonna stick raw vac to the actuator and see what the turbo does.......

Jack, nah never removed the undertray, good idea there.

Heres a laugh....I had my Legacy GT in a local recommended garage the other day, to get the up pipe welded to the second turbo as it was blowing. I pick the car up, and the mechanic says "its still blowing under a shielded metal thing, we're not sure what is in there....I'll show you the bit" as he lifted the bonnet and pointed to this "thing"....

"that's the 2nd turbo mate" I said......."so wtf did you weld....?"

that turbo is the size of a house! and kinda....well.....turbo-shaped....Sheesh.....needless to say the car wont be going back there....he was well embarrassed and only took £100 for changing the engine cradle and steering rack. In his defence he said he "hasnt worked on a Subaru turbo before"......."no ****" I said

 

[ScottyP45]

Update:

replumbed all tubing in silicon from scratch, and used the N18 as a N75 as it was mint and the N75 was grotty from where it used to live.....and on that note, I relocated it to the top. Snapped the nipple off the vac reservoir which was hanging by a thread.....so off to the breakers for another one!

Guess what? Still getting limp mode.....AAAAAAAAAAAAAAAAAAAAARGH! The VNT actuator is squeaking at the diaphragm, and its sticky returning to rest, which would not cause underboost, but can the actuator be removed without taking the turbo off? It moves but maybe not far enough, however I still hear hissing so have to hit the plumbers merchant to get bits for a boost leak tester. It takes quite a bit of force using my fingers on the bottom of the rod, to lift it up and the spring return is strong, is that normal? I think it would be, but just checking if anyone has felt it before in the same way - was it easy or hard to lift the rod by hand?

ALso - when you look thru the gap under the bumper, you see the rad, and a long black hard plastic pipe under it running across the bottom....that has a threaded hole in it with no bolt - what is that pipe?

Heres the pile of crap I removed:

Much more space down there now: (I know the hose is missing to the turbo in this pic - no prizes for spotting that lol)

 

[aragorn]

The only thing i can think of below the rad is the boost carrier that takes the charge from the compressor outlet over to the intercooler?

Its also afaik metal rather than plastic?

 

[ScottyP45]

aye thats the one mate, its plastic coated but is the boost pipe to the cooler. I thought it was but got concerned about the threaded hole in the front of it, looks like a drain plug hole with the plug missing, but think its a dummy mount for something else to join to the pipe on another model?

 

[fARQUARE]

could a sticky actuator not feasibly cause over/underboost issues depending on where and how it sticks?

as soon as the ecu goes over 200mb difference between requested v's actual it will go into limp. So it sounds to me like the actuator might be the issue but if the actuator is sticking i'd have thought thats more to do with sticky vanes rather than a bad actuator which would loose pressure if the diafram was split..
you can remove it with the turbo in situ, i had to loosten the mounting bolts to mine to get the inlet bolts out. There is a procedure on club tdi that tells you how to re-set the actuator durations if you fit a new unit. Not sure who suplies them in the uk though

 

[ScottyP45]

nice one mate, will see if I can get it off for a look. What happens is the rod is stiff to lift under spring pressure with your fingers, and the actuator squeaks (or more like a squawk) as it is released again, and sticks on the way down, so not opening the vanes properly when it goes to idle, so wouldnt think that would cause underboost, which seems to be the problem. It stops, but you can push it down further.

I have the bits now to make a boost leak tester, and will test it tomorrow. I have a suspicion that it has a leak, but if not the actuator and / or turbo will have to come off, and the legacy needs the new cat fitted plus a turbo gasket before I can use that while the tdi is off the road for a day or two, so I can clean the inlet and turbo out good...

 

[ScottyP45]

ok, I found the boost leak, and fixed it! Yaaaaay!! A short section of rubber that links the plastic boost pipe with the intake manifold was split neatly round the jubilee clip edge on the bottom. CHecked the others, fine.

Now im getting crazy fecking overboost, 2 bar if you let it, before 3k. It hits a bar as soon as it passes 2k, and seems to have less power now with more boost, too much air and not enough fuel pressure I guess.....so im gonna have to make some kinda leak-off device till I can get the turbo and actuator off as I start night shift tonight and need to use it.....good news is my new vag coms arrived - w00t

 

[tdia4]

Was going to mention that bit aswell, seems to be a pretty common place to split, Which pipe have you linked your boost gauge to? Want to see what mines running at compared to standard.

I replaced a few of my vac pipes the other day because a few were getting frayed, went to do the one in the ecu but it must be me being blind because i couldnt see one anywhere lol.

 

[ScottyP45]

the boost gauge is tee'd into the map sensor tube from the inlet to the ecu, so it reads proper inlet pressure.

If you have an AFN or AHU motor then theres a thin black tube that runs up the inside of the ecu harness, goes from the horizontal black plastic intake pipe (on a stub underneath it), to the ecu metal casing - then to a stub, but inside the actual ecu guts, there is another tube from that casing stub to the internal ecu map sensor - thats been replaced now too on mine, watch you dont snap the nipple off the map sensor, or its all over

The map sensor is soldered into the ecu circuit board and not available separately.....so if you snap it off, its new ecu time.....use a blade to slit the rubber tube at the ends so it can be removed.

You can only see the ends of the original map tube before you cut it off, but theres a bulkhead grommet and one on the ecu compartment that a new pipe can be threaded thru:

I did an excellent suggested test from a tdiclub member, pull the pipe off the vnt actuator and drive...if you get heaps of low down boost, the vanes are jammed shut or nearly, and if none till 2.5k rpm, its fine. Mines was shut, bags of boost with no N75 control to the actuator, so im gonna chemical clean it with oven cleaner without removing the turbo, just spray the caustic foam thru the egr pipe hole in the exhaust mani, into the turbo exhaust housing. but for now, I tee'd the N75 atmosphere port into the map boost line, so every time the ecu shut the valve when i lifted off, the boost pushes down on the actuator, eventually closing it and freeing it up a bit, so now I get 1.5 bar instead of 2 bar, still not perfect so I have introduced a controlled leak in the boost pipe (a beer tap off a brewing barrel) to bleed off enough so it can only hit 1.2 bar (usual standard max requested by ecu) and now no limp mode.

Out of interest to others, even with 2 bar (almost 30psi) of boost, power was actually weaker due to more air but no extra fuel being injected, so as i have said before, more boost than you need to burn the available fuel on a diesel, has zero effect, except lifting the head! Now, if I up the fuel pressure with my increased boost, thats a different story lol.....

 

[hiltoa]

Hi - I've been following this thread with interest as I've had a persistent limp mode on my A4 TDi (115PD) - I feel it's a good time for me to post as I've finally sorted it. (touch wood!)

When I got the car (with 172,000 miles on it) it would hit limp mode if you went over 2400 revs under load, which was a great bargaining tool!
I fixed this symptom pretty fast with some 'italian tuning' - i.e. caning it about > 4k revs as much as I could (once warm of course) to burn off the worst of the deposits that were obviously clogging the turbo's vanes. It's very satisfying to fix such an obvious issue by just driving hard.

However, I was still getting limp mode at motorway speeds under load. It was worse when I had a bit of weight in the car, and/or going up motorway inclines. VagCom gave the overboost code.

I replaced the vacuum line to the VNT actuator - no difference
I removed the EGT / anti surge housing and cleaned out all the sludge - no difference
I blocked off the EGT to exhaust connection - no difference to limp mode, but the hunting / lumpy idle was fixed - Yay!
I used Innotec to clean the hot side of the turbo = no difference (aaargh!)
Finally, I replaced the equivalent hose to the one that evilscotsman recently changed (it's a 90 degree bend on the 115PD) and voila - no limp mode! She'll now happily cruise uphill on a private runway at a speed to match her official horsepower!

The hose I replaced wasn't obviously split but was looking tired around the jubilee clips and felt overly 'soft' - I can only imagine it was leaking slightly when warm and at full boost.

I hope this helps with anyone chasing that annoying motorway limp. For the sake of £25 refresh that hose!

 

[ScottyP45]

its a nightmare eh!

Mine is confirmed down to sticking vanes either caused by the actuator or the vnt ring in the turbo, the arm pulls up ok but wont drop down fully, its getting a chemical clean next. Its been soaked in loosening agent on the outside, and worked up and down....I have to put over 10psi of air on the vnt actuator to close it, but at first it took 20, so its a bit free-er and now overboosts but less limp mode events due to an introduced bleed to keep the max boost at 1.5 bar.

Easy-off is the preferred chemical but not sure if its obtainable in the UK, however Mr muscle oven cleaner or cillit bang should do the trick, as a point of interest nothing, and I mean nothing, can physically dissolve carbon, its nearly indestructible. Only "piranha fluid" is capable of lifting it off clean and kind of dissolving it, but thats a deadly mixture of 2 acids that is used to clean glass lab-ware and is an extremely powerful oxidiser, strongly acidic and is also exothermic - it instantly goes to 120 deg C when mixed together so not really suitable for home use.

I will post the result of the cleaning soon, its going in thru the egr hole into the hotwheel end and will sit overnight if need be until the lever moves smoothly....now to find a foaming powerful bbq cleaner.......

Also my viton pump head seal kit is here, so the leak from the IP will soon be a memory (I hope lol) as its getting tackled this week too. (I lose a quarter litre every time its parked until the pressure drops in the pump..)

 

[Izzy1]

seem's like a common fault. My turbo vains are sticking also. i'm trying to find a cheap replacment turbo to just stick in.
I've just resulted in driving the car more calmer and avoid going over 65mph. good thing i don't have to use the motorway to get to work.
just end up using the VW for motorway journeys.
Let us know how you get on with cleaning the turbo. will be willing to give mine a clean if you have a special mix to get rid of all the build up in the vains.

 

[aragorn]

why not just take the turbo off and clean it out?

 

[Izzy1]

would i need to replace all the gaskets? or could i re-use the current ones?

 

[ScottyP45]

I think they are metal anyway mate so can be reused, the chemical cleans the yank boys have done on tdiclub have all been successful with only one guy having a jammed actuator instead and chemical didnt work so good, they just use oven cleaner, easy-off or similar.

Involves either take the down pipe off and spray in the turbine housing from there or take the egr corrugated pipe off at the bottom and tube the foam down into the exhaust turbine that way, fill with foam, spin inducer end with a finger (intake tube off) to fling the foam round, try moving vnt lever and repeat until it moves smoothly, one guy only needed 30 mins while some had to leave it on a few hours to work. Do NOT put anything in the intake end of the turbo, just need the rubber tube off to spin the turbine with your finger tip to distribute the foam round the outside edge where the vnt ring lives.

The turbo obviously could be taken off but not advisable to dismantle it unless your confident of putting the vnt mechanism back together correctly and not snapping any bolts in the housing...so chemical is a first base option.

Stripping it isnt brain surgery but is open to several pitfalls so I would only do it if I really had to. Taking it off to clean it is a good idea though, but not strictly necessary. They also just blow the remnants of the foam out the exhaust, no rinsing or anything.

Chemical cleaning for turbo vs removal? - Page 4 - TDIClub Forums

Im gonna tackle my injection pump head seal today I reckon as well.....sick of the diesel falling out lol