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'05 Mk 4 Jetta (PD). Sporadically misfired several weeks ago (with no trouble light, so no code). New fuel filter eliminated the problem for a few weeks. Problem recurred (again, without a trouble light). Finally got a light a few days ago (which extinguished on next start).

Now, off to dealer. Code was stored & indicated #3 injector open. Dealer advised:
(1) Check wiring, but only 10% probability this is the issue.
(2) Replace ENTIRE head because (a) injector is not designed to be replaced and (b) "their experience" is head usually warps at the injector seat, precluding proper seating of injector, which is why it misfires. They'll replace head for ~$5500.

Told dealer to go ahead & check for electrical prob. Also that there's NO basis for a diesel head to warp that's been properly maintained & never overheated (160k miles on engine). If heads are warping under normal conditions, that's a design flaw.

Suspect dealer is blowing smoke up my tailpipe... pretty sure injectors CAN be replaced, also that there's no reason head should be warped at injector seat - thoughts?

Thanks for mulling this over. -Ken
 

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Hm....injectors can be replaced fine. Yes the head can warp at the injector but it's not a normal thing.

A more likely scenario is camshaft wear, improper camshaft timing, or other sensor problem. Camshaft wear should be felt at idle, will throw no codes: http://www.myturbodiesel.com/1000q/multi/camshaft-inspection-replace-vw-tdi.htm

If #3 injector is open it's possible there is a fault in the injector wiring harness. Check the round connector on the head and all the wiring. By now it's possible the wiring harness has chafed somewhere.
 

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Thank you for assistance

Thanks for the insight. The car runs like a clock at idle, so cam wear does seem unlikely.

I ok'd the dealer to pull the cover & check the wiring. They could not find any electrical fault, but they did clean the connector contacts. On restart, they report no misfires (but the problem is only intermittent, so time will tell). I originally suspected a dirty connector mating or a frayed wire & expect either could cause partial functioning with no engine malfunction code until the electrical resistance grew significantly.

I'm still taken aback by the "replace the head" recommendation, so I plan to contact VW to corroborate/refute whether this is a VW recommendation or the local dealer's recommendation. It's completely reasonable that an injector/wire/connector might fail in 160k miles. If it's VW's, it's outrageous that the entire head reliability is reduced to MTBF of injectors (whether because injector seat actually do warp or for some other reason). :BS

Thank you again -Ken
 
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