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VNT Turbo Rebuilds - Cheap! General TDi Information TDi's and Vegoil TDi Cambelts & Diagnostics ***NEW - full recon turbo, new gaskets, 12 month unlimited miles warranty, FITTED, £675!!! EG GT1749VA on 2.0PD engine, most 1.9tdi/1.9PD under 150hp. See bottom of page*** Losing power? In 'limp home' mode? Restart car and it's okay, till you accelerate a bit and it's like someone killed your engine? Did it get progressively worse? Diagnosed turbo fault? Read on, save £££'s
The VW TDi engine is equipped, like many modern diesels, with a Variable Vane turbocharger. The problem is that if the car is not regularly run to 3,000rpm between gears or is 'babied' and 'coasted' along the road like an 'old mans driving' the VNT vanes, which are in the exhaust flow, get sooted up and without the exercise they eventually stick. The prevention is to never run the engine below 1,500rpm when driving and try to change gear at 2,500-3,000rpm when warm (try not to exceed 2,500rpm when the engine is cold unless you have to) and every now and then go full throttle to 4,000rpm. This blows the turbo through and gives the vanes some exercise as the revs and power increases they have to move from one extreme (full boost) to the other extreme (low boost). This exercise keeps them healthy.
The symptoms of a VNT failure are a fault code indicating 'positive boost pressure deviation - intermittent' and a car that has driven fine, but under acceleration it feels like someone has switched the turbo off and until you turn off the car it runs like a 1.0 litre engine. Once re-started, the car runs great till you accelerate, typically over 2,500rpm, when it kills the power (this is called limp home mode, where the engine goes to emergency minimum power mode because it knows something is wrong). So you begin to drive avoiding high rpm and acceleration; this works for a while, until you notice the car has started to go into limp home mode at 2,000rpm. So you drive it even more gently. Eventually, just pulling out your drive will kick it into limp home mode and you struggle to even get 70mph out of the car, with minimal acceleration. Technically, the VNT mechanism is now stuck and the ECU detects that it is not doing it's job (sensed by far too high pressure coming from the turbo). To avoid the engine blowing up, it cuts the fuel and logs a fault code. Restarting the engine the ECU will try to behave normally until it re-detects the unfixed fault and puts you back into limp home mode. This problem can happen on any VNT turbo, but is well known on the VW group 110hp engine. The sad thing is that your actual turbo, the vanes and the oil seals etc, are probably fine. If you haven't noticed undue burning oil, blue smoke or any other performance issue prior to the 'cutting out of power' then the core of the turbo is probably fine. Normally the turbo lasts about 300,000 miles so very high mile (200,000+) units may benefit from a new/recon turbo as a precaution. For the rest of us - it's purely an issue with the VNT control system on the turbo, not the turbo it's self. The traditional fix has been to have a recon turbo at a price of around £600. Recently some turbo specialists have been able to rebuild your VNT only, leaving the core of the turbo untouched, for £250ish if you take it to them. **We offer an in house rebuild of your VNT system for £125 by post or we can remove/refit as well if you are local for additional £150 (inc new genuine gaskets & our stainless fittings etc). This can save you £500+ over a new/recon turbo and has proven popular since we introduced it under a year ago** We have been able to offer this service which is a full strip down of your seized up turbo VNT, new stainless steel bolts and screws to refit (the old ones will nearly always be rusted up with heads rounded off), rebuilt and returned to you. Your local mechanic, or yourself, if you are competent, can remove the unit, send to us and refit. Typical turn around is 7 days but sometimes we can get them out next day. After cleaning and stripping down your VNT parts look like the pictures shown below after cleaning (they look like a solid black mass before, indeed the case may need splitting as it will be ruse welded together).
As they say on blue peter, that is one we made earlier. Please contact us to discuss a rebuild, there are other items such as vacuum hosing and N75 valves that can cause the issue. Generally we would advise a VW specialist to run an N75 output test, or simply start the car and watch if the VNT actuator rod moves it's full 3/4 inch. If that doesn't happen, you test the vacuum on the actuator and apply direct vacuum to it (to eliminate a faulty actuator). If that doesn't highlight a faulty actuator, then unbolt the actuator from the turbo (two M6 10mm headed nuts, access via under the car on transverse engines) and move the lever directly by hand. The actuator MUST be unbolted and free (you don't need to disconnect the circlip) from it's mount or you'll be pushing against the stiff actuator spring. The leaver should move freely with the barest touch of pressure a full 3/4 inch movement (2cm). It should have NO resistance and go freely from stop to stop. There should be NO lumpiness or stickiness. If the lever is sticky or feels jammed, or only moves a little bit, there is your problem. The VNT needs rebuilding. Please note we cannot diagnose your car remotely, you need to make sure the VNT lever is actually stuck/sticky before assuming it's the turbo causing the problem. There may also be other problems with the car, all we can do if you send us the turbo is fix the VNT! While 90% of cars with this issue it will be the VNT, some are due to the piping cracking, faulty N75 valve or other issue can crop up and diagnosis is a good idea. ALSO please note, you have to be confident there isn't too much shaft play/leaks/blue smoke/burning oil or other general turbo issue. This is not a recon of the turbo, it's a service for people who have a good turbo but faulty VNT causing overboost codes and 'limp home' mode. If your turbo is in doubt of burning oil or being on it's last legs, have a full recon at your local turbo specialists. If your turbo has always behaved perfectly up to this VNT problem, send it to us. If you live locally we can carry out a 90% probability diagnosis and do the removal/refitting work for you.
It is also worth cleaning the intake manifold,
ports and blanking the EGR with a solid metal gasket to disable it.
This is because the EGR system cokes up your inlet and pushes more
soot through the sytem, adding to the problem. It isn't needed
for MOT and the car runs better without it, it's part of the 'new
car type approval' gubbins to meet regulations of some emissions, at
the expense of engine health, economy, power and other emissions.
Get your mechanic to do this while waiting for the turbo or get us
to do it if you are local. As the inlet manifold usually has
to come off to fit the turbo, it's a good idea. You'll also
need turbo/manifold/downpipe/inlet manifold gaskets, new bolts for
the exhaust manifold and downpipe gaskets (we use stainless only)
and possibliy an oil supply/drain pipe if they didn't come off
cleanly. Get your mechanic to order them in while waiting for the
turbo so you are not held up. |
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