The tdi's are notoriously
smoky, often having to be de-tuned to pass the SVA and MOT, (sometimes
left like this leaving the engine response as flat as a pancake),
however you shouldn't be trailing smog during normal driving, typically
you'll see it on startup and during hard acceleration.
Any number of things can
cause smoking, including worn injectors, poor tuning and more, but a
regular note, on which we've had mixed, but mostly positive messages, is
that the Exhaust Gas Recirculation, (EGR), valve can be disconnected to
prevent belching on startup.
The EGR valve, shaped like a
small metal flying saucer and located on the inlet manifold, can become
stuck or corroded leading to the symptoms above, (Haynes, chapter 6.6
fully describes the function of the valve).
Disconnecting the rubber hose
from the valve and blocking the end has been found to resolve the
belch-on-startup problem, with no negative impact on the normal running
of the engine, one club member simply inserted a close-fitting
ball-bearing and reconnected the hose.
To make a permanent fix, the only real cure is to remove the gasket between
the valve and inlet manifold and replace it with a thin solid plate, thereby
completely removing any route for the gases to escape. What you need to do is remove the two horizontal bolts which attach it to the inlet manifold and carefully slide out the gasket, then replace the gasket with a thin piece of alloy plate, if you can find it, you can use a piece of 25 thou. aircraft alloy.
An alternative school of
thought suggests that as the EGR valve is installed, it's there for a
purpose and needs some simple maintenance in order to ensure good
service. Club member Ron offers the following advice:
"Attention all, cleaning the EGR is simple and cheap, I did mine after weeks of running probs.
(1) Obtain new EGR gasket (main dealer £1.35)
(2) Buy 1 Large Bottle STP Fuel Injector Cleaner £9.99 & 1 can of Carb/Fuel Injector cleaner £4.75.
(3) Remove EGR and place it in a small plastic tub containing all the STP, leave to soak overnight, take out dry and clean, spray lots of Carb/Fuel cleaner inside to blow out any crap then blow out with air line or pressure pump.
(4) Clean up both faces that take the new gasket.
(5) Remove other end of vacuum pipe and spray through with Carb/Fuel cleaner, replace vacuum pipe and EGR with new gasket.
Job done, Cost £16.09. The inside of my EGR was like brand new when I finished and the drive/fuel economy are great, if repeated once every 6 months you want get any probs with the infamous EGR.
Judging by the overwhelming
debate on the club forum, I see this is going to run and run ... at the
end of the day, you have three options :
1/ Replace the EGR valve, I
checked this out and it's over £200 from MMC
2/ Service the valve twice a
year at £20 a time
3/ Block the valve off.
You and the MOT inspector
will have to make the final decision, unless we can get a definitive
response from MMC.