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2006 Touareg V8
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Discussion Starter · #1 · (Edited)
I have a 2006 V8

Bought used with a list of problems.
Seems to run good, smooth idle, plenty of power, no fluid leaks or noises.
After scanning with VCDS I decided to start with the Engine codes first.
P0304 cylinder 4 misfire
There is also a few codes related to the Bank 1 Sensor 2 O2 sensor.
(Am I correct that is the passenger side sensor after the catalytic convertor?)
The new O2 sensor arrived today just as I was giving up for the night, but I will install it next.
I changed the oil (Mobil 1 5w30 syn), oil filter (Mahle), air filters (Mahle), spark plugs (denso iridium), installed a new coil pack (Bosch) on cylinder 4.
Someone had started working on it and had already installed a red top coil on #4 (the only red top coil on engine, the rest are black).
Removed the bushings on the front of the intake flap shafts, cleaned, lubed, reinstalled.
(both are very smooth now and have the upgraded aluminum linkage rods on both)
Compression check shows readings from 175 psi (8) down to 162 psi (5). Cylinder 4 has 165 psi.
Engine still sounds fine, plenty of power, no odd noises or vibrations.
Still getting a misfire cylinder 4,
I cleared all codes after work was completed and check engine light came back on as soon as I started it. Misfire Cylinder 4. Misfire count seem very low to set a code at 2 misfires.
I am giving up for today, I did switch coils between #3 and #4 and will scan again tomorrow and see if the misfire moved. I highly doubt it as #4 had a brand new coil and spark plug.

My next step, after installing new O2 sensor is to check PCV valve for leaks as it is nearest to #4. Then I plan on moving on to swapping injectors between #3 and #4 to see if it moves.

Any help, tips, or advice are appreciated.
I am new to the 4.2 V8 and learning as I go.
If anyone has questions about VW ALH diesel engines I would be glad to help as I know them very well.

I am attaching a picture of the original spark plug that was in #4 just for reference if it helps at all.
Computer keyboard Peripheral Household hardware Input device Engineering
 

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2006 Touareg V8
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15 Posts
Discussion Starter · #3 ·
PCV valve was TOAST. Lots of sludge and the rubber diaphragm was a semi soft goo. It has been replaced.
 

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2006 Touareg V8
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Discussion Starter · #5 ·
Check engine light was gone, didn't come back after 12 mile drive. Next day I was in the driveway revving up the engine and the check engine light came on for about 30 seconds and then turned off by itself. Haven't scanned it yet, but I will keep you posted.
 

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2006 Touareg V8
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Discussion Starter · #7 ·
Just to post the fix I found to my misfire cylinder 4:

This is probably not going to be a common problem or repair for most but it was just my luck.

I installed a set of new (reman) injectors and still had misfire cylinder 4.

Pulled out my noid light set and checked #4 (should have done this first)

No pulse signal to #4 from the ECU.

I removed the ECU, checked that there was no corrosion on the connections and that everything looked good. Then I started unravelling the insulation on the smaller ECU connector going toward the firewall. Pin 88 (Brown / Green) wire had no damage all the way to the firewall. I was just about to start uncovering the wiring from the firewall to the engine / injector and decided to actually de-pin the terminal and inspect the female pin.

I could tell someone had been in this wiring harness before from the poor quality job they did taping it back up. Sure enough when I pulled terminal 88 out of the small ECU connector it was fairly mangled. It looked as if someone was trying to probe it with something too large and damaged it pretty good.

Luckily I has some VW wiring harnesses in the shed and a terminal from a 2003 Jetta TCU was the same size. I created my own "repair wire" and low and behold I now have a firing injector #4. I verified this with the noid light but have yet to drive it until tomorrow. If this didn't fix my misfire I will re-post here but I am 99 percent sure it is resolved.

I remember an old mechanic I worked with telling me a story about chasing zebras when you should be looking for horses. This is one Zebra I should have chased but it is such an unthinkable problem my mind never went there.
 
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