.: Workshop Casebook

This owner came to us (with her car on the back of an AA truck!) with a really rough, uneven idle, unwilliness to rev & lots of smoke & noise.

Starting with a full diagnostic scan with our VCDS software, the codes revealed a "misfire cylinder 2". We initially suspected a faulty PD injector, a fairly common fault on VAG cars. As these injectors are hideously expensive we decided to get our Picoscope Automotive Osciloscope out & confirm the injector current & voltages etc before going any further. We could see from the images that although the current was roughly correct at around 18A, the profile did not look correct. However, all 4 injectors were showing current draw (& hence voltage & earth paths must be correct), so we beleived that #2 injector may have an internal mechanical issue.

The cam-cover was removed & the in-head wiring loom examined (another weak design area - whoever thought putting a wiring loom & electrical conectors inside the engine bathed in 100 degree oil was an idiot!). This loom looked ok and bench-tested ok, so we left it (although these have been known to fail under load).

We then removed the glow plugs & noted that #2 was very clean compared to the others. This tied with our theory that #2 cylinder wasnt firing & also tied with the misfire code. Before going any further we decided to check the cam timing. On hand-cranking the engine over it had a noticable tight spot & generally didnt feel right. The cam timing was also found to be way out. We suspected some kind of internal damage, so after discussion with the customer the cylinder head was removed.

What greated us was a horror story - #2 cylinder had obviously not been firing for a long time as the piston crown looked nearly new (either that or it had received a new piston at some stage)! But, the main issue was the exhaust valve in cylinder #1 had broken off & was embedded in the piston crown!

Long-story-short, we had to remove the sump to access the big end bolts, whereupon we found another glorious design failure in that the oil pump drive chain tensioner had self-destructed allowing the chain to flap & become damaged, another common failure! Most of the broken bits of tensioner & steel spring were loose in the sump. We renewed the chain drive & tensioner assembly, removed the piston & renewed it, reassembled the block & fitted a new reconditioned cylinder head, a new injector in #2 and set everything back up with a new cambelt kit & water pump. All throughout the rebuild process new stretch bolts & gaskets were fitted where required to ensure a long & reliable repair.

The car fired first time and idled perfectly. Looking at the dynamic injector dats showed that all cylinders were now firing as expected with correct & stable fuel corrections. The car was test-driven and we are happy to report that the owner says it now drives better and smoother than it has since she first bought it !

Another satisfied customer!