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Hey all-

Brand new to the forum, so apologize if I am posting in the wrong area, or missing relevant information. I am desperately seeking help as I cannot find the issue. Here's the run down.

I have a 2008 Touareg 2, V8, 4.2L.

I bought it used (~95k miles) and almost immediately had an issue. #5 is misfiring. Since then, it has been in the shop 10-12 times with no resolution. Here is what I have done so far:

  • Put in all new plugs/coils
  • sent the ECU to SIA electronics in Chicago for testing - no errors
  • replaced the injector with a new injector on #5
  • swapped #1 for #5 (plugs/coils)
  • checked the harness (dealership said they did this, but not sure if they did or are just tired of me)

Through all this, #5 is still misfiring. The dealership is out of options, suggesting that the ECU is faulty and needs to be replaced ($1600) or they need to swap the #5 injector with #1 to see if that is the issue (~$1000+). Neither of these options sound reasonable because a) the ECU was already tested and b) the injector is brand new, yet the exact problem (#5 misfire) has persisted before and after the injector replacement.

What the hell do I do?!?
 

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I take it the misfire is turning up on a scan , which would seem to indicate that the issue is electrical.
 

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Not necessarily... the ECU can register misfires for a multitude of reasons. The OP has already troubleshooted the common culprits.

Could do a smoke/pressure test, to rule out a vacuum leak. Though, usually that would cause the misfires to skip around... not stay in one cylinder.
 

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Outside of cam lobe wear, loss of compression on that cylinder, or I guess excess carbon build up (manifested mostly on one specific cylinder?), I decided to throw a long shot in since everything else is covered:

One important thing is you just purchased this...sometimes dealers detail the engine and get water where it doesn't belong. Seeing as all cylinder components have been replaced you might take a close look at the specific injector plug, coil pack plug (clips into coil pack) and so on. Water can get under the insulation and cause hell. To make matters worse, sometimes there is nothing visibly there and it can happen after the fact (water sometimes has to turn to vapor to enter). Traditional electrical scanning and testing might not work as expected here too.

Again a long shot...but what the heck
 

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Not necessarily... the ECU can register misfires for a multitude of reasons. The OP has already troubleshooted the common culprits.

Could do a smoke/pressure test, to rule out a vacuum leak. Though, usually that would cause the misfires to skip around... not stay in one cylinder.
The scan will tell you the issue if it is registered in the ECU !
 

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I'm experiencing the identical problem with my '04 V8. I injected Power Foam to clear carbon build up. This drastically helped to loosen diaphrams, but #5 misfire still exists. I've changed the injector, the coil and now the plug. Changed the plug but the problem continues and in addition trans now shifts and higher rpm. At times the problem disappears but when I sit at a light, at idle, the problem returns.
 

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My UNSoLVABLE Problem SOLVED and I hope this helps you! I don't know who, how or when, but examining the diaphragms I (dumb luck) noticed that the bolts to the intake manifold were all loose. Problem resolved!!!!! No codes, no dropped cylinder and she rides as good as the day I bought her!!!!!. Even though all bolts were loose, it only registered as a misfire on 5.Good Luck
 

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Phew, that's very good news. Well done!
 

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A diaphragm is a barrier method of contraception used by women
Have not seen one in a car for a looooooooooong time
 

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Pull the intake manifold off which is a fairly simple job, make sure to have new gaskets and injector seals on hand. Based on the mileage and work already done, it would be very likely that carbon is your issue...
 
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