150tdi. No power til 2500+rpm Update 7th May

Well had the mk4 gt tdi for 3 days, and there's a problem from the off.

Basically, when you pull off/accelerate I can here the turbo spinning up quite loudly but there's no power until 2500rpm+
Sometimes it'll pull ok from 2k but usually it doesn't.

Now her ani. 150 boosts hard from 1500rpm but mine is rather crap tbh.

I've changed the MAF for a VAG item, oil change/filter, fuel/air filter etc

Could it be the N75 valve??

I've checked all the main boost pipes as I know they have tendency to leak or blow off, but all seems ok.

Oh, had it on VAg Com but there's no fault codes coming up.

 

turbo lag??? ( i have no idea just guessing )

 

Nah, it's really odd, if I feather the throttle on and off it'll get better, but it's not quite right.
her 150 will wheel spin right away, where as this piece of crap won't pull my 4skin back.

 

A shot in the dark - jippy wastegate or actuator? But you probably knew that

How many miles on it?

 

Duff turbo? Maybe the impeller has come off or lose on the compressor side?

 

Has done 140k so I'm not ruling out a turbo problem.
It's odd how it'll boost ok from 3k though, and quite hard too, but not below 2k, it just feels so sluggish compared to other 150's I've driven.

 

it could well be a stuck waste gate, that would make it as laggy as hell.

check the smaller vac pipes for leaks, theres one that goes right down to the blow off valve too, thats always alittle close to things my old one look as manky as hell untill i replaced them all

 

my guess is stuck wastegate or n75 valve

 

definately worth checking the egr valve

 

On the back of the turbo, drivers side, there's a plunge valve what I'm assuming is the waste gate.
Should I be able to just push it in and out with ease?

EGR?? Come one now, I'm a valver man turbo's and diesels are a new thing to me totally

 

Doubt it as the diesels dont have wastegates, they have variable geometry nozzles, which put simply is a movable ring in the exhaust side which alters the output of the turbo, over time these gradually "coke" up with soot altering the performance of the turbo. It is a common fault with the PD diesels and Im suprised yours has made it to 140k without a new turbo!. Best bet is to get the turbo off and sent to a GOOD turbo specialist for a rebuild.

 

no way about the turbo rebuild. i had one at 155k miles, no problems

they can get coked up if the engine is running crap but on freds tdi site its not uncommon for them to be curable just by manipulating the actuator manually to free them

 

can you get a pic of it mate? they all effectively have the same layout but orientation will be different to what i was used to cos mine were in A4s which were longitudinal.

i think youve found the actuator. thats the arm that controls those variable vanes (as has been said, they have no wastegate)

this will be hard ish to move as it is spring loaded.

i could move mine about with needle nose pliars without much trouble

 

HAHA!! if you say so....

they have the variable vane turbos which alter the nozzle, these do coke up some time but if they stick you get masses of boost get to 2k then it shuts down as it detects over boost, they do have a waste gate which dumps the excess boost into the exhaust system...all turbos have this as variable vane alone will not stop over boosting.

also a PD will do millions of miles with out needing a re-build i wish people would stop saying they need rebuilding etc at low miles!! mine now done 186k and the turbo bearing showed no signs of wear at 179k when we did the cam belt etc, if they are looked after and driven properly they will just keep going for 300k easy!

on the EGR valve this is the metal bit just before the inlet manifold, it has a flap inside. pop the 90deg boost pipe off, and undo the 3 bolts and take it off, it will be gummed up and narrow, get the old brake cleaner out, leave it to soke and then scrape off the soot, refit and this will add some power too, (i had a 1/2" layer on mine at 179k cleaned up and its fine... just make sure every so often youy give the car a spanking when its HOT as this helps clear out the soot from the gubbins).

 

Righty, the bit I could move was the valve for the EGR . As said I'm not too hot on turbo's
Looks like the last person thought the same as it was pretty good inside, and the bolts were rounded , just like the sump having no threads for the plug The actuator arm works fine and the plunger will go up and down freely, so thats the EGR eliminated.

I havent' actually got to the turbo yet, I'm assuming it's tucked away down the back. I've just heard about the variable vanes. You can work them free and they'll be good again, just a case of getting it down the old mans on the ramp and whipping it off.

Would the MAP sensor on the front be causing a problem too? Just a thought.

 

the egr valve should close completely. it might be worth unplugging the vac hose to it (and plugging the vac hose) and driving it again)

as for the sump, winds me up no end when these get over torqued and people kill them

a 20vt i was working on had the hole welded over haha

 

in my opinion your variable vanes are stuck. The idea of this is that you can use a larger turbo to do the job of a smaller one at lower rpm by adjusting the vanes inside which adjust the size of the exhaust housing.

turbo technics charge a couple of hundred pound to remove and skim the vanes, or you can take the turbo apart and leave it to soak in petrol and carb cleaner and then scrub it all off.

hope this helps as it sorted the mk4 that came into my friend's garage recently

 

This is the next job to do. Take it off and clean it down.
Fingers crossed this weekend, and I'll let you know the results.

 

Other than the horrendous guesswork posted in this thread, the thing concerning me is.....

It isn't a job to be taken on lightly, believe me.

 

if the vanes are stuck, just wiggle the actuator arm, ive known quite a few people to free them that way, and then work out why ive overfueling and sooting stuff up and making them stick