[s-cars] LAC troubleshooting 2.0T coils

[Varon H. Fugman]

Specifically troubleshooting 2.0T coils when they are installed in a 2.0T
FSI motor in an '07 VW Jetta (thus the LAC. but not NAC. wait, the Audi part
will come.)

 

The backstory:  Driving the Jetta to work this morning, got to an empty
stretch of highway dropped it into 5th, punched it, and the check engine
light came on, accompanied by rough running and reduced power.  Made it the
rest of the way to work and concluded it was probable I had a coil failure,
but can't even see the coils with the stupid plastic cover over the engine.
Nursed it home after work (getting 45mpg according to the trip computer.
maybe there's something to this cylinder "deactivation"!)

 

Popped off the plastic cover (with integrated air filter and MAF-some
engineer must have gotten a big bonus for reducing part count!-and the coils
were visible.  But no sign of injectors.  Of course, being a
direct-injection engine they are buried somewhere deep inside the valve
cover which means I couldn't go unplugging injectors to isolate the failed
coil.

 

(The ECU may know which coil has failed.  I suspect if cut off injection to
that cylinder.  But I haven't gotten VAG/COM with the correct cable for this
car yet, and these OBD II cars aren't as willing to give up their secrets as
the pre-OBD II S6!)

 

Here comes the Audi part. without an easy way to test the coils in the
Jetta, I just pulled all 4 of them out of the Jetta and put them in the S6
(I'm running 2.0T coils with an 034 harness.)  Now I could unplug injectors
and quickly determined the #3 was dead.  Using my spare coil from the trunk
of the S6, I put the Jetta back together and now it is happy.  I think I'll
buy a set of 4 new coils of the latest revision for the Jetta and keep the
good used ones as emergency spares.

 

Coil-on-plug has a lot of advantages, but coil life is not one of them!  The
poor things do a have a pretty brutal (hot) life.  At least these are cheap
and easy to change.

 

Varon

'07 VW Jetta 2.0T

'95 urS6 coil tester