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More Audi fun P0133 and P0304

February 3, 2010

The turbo upgrade to the K04 was a success and the car ran great for several weeks before some new gremlins crept in.   Our ’99 A4 Quattro developed an intermittent miss and stutter under part throttle.  The check engine light came on and trouble code P0304 – cylinder #4 mis-fire reported via the scan tool.  

Raising the hood and listening closely, I could detect an air leak, which turned out to be a cracked plastic breather pipe next to the dipstick, below the intake manifold.  A vacuum leak could affect the mixture, and create a lean mis-fire, I reasoned. This was a plastic “L” shaped piece that provided crankcase venting, and connected to some metal hard piping that routed around the engine and connected to a one way pop off valve on the intake hose leading to the turbo.  No doubt, while moving this metal piping around while doing the prior turbo install, I unknowingly cracked the plastic breather pipe on the other end.   After curing the intake leak, I reset the code and test drove the car.  The missing symptom returned after the car warmed up a few miles down the road.   While the broken pipe needed to be replaced, if I had really thought about this objectively, I would have concluded that I should have seen multiple misfire codes, and not just the #4 since the leak fed back into the intake side of the turbo and not into a port on the intake manifold in proximity to #4.

Pulling the codes, I found P0133 and P0304 again.   Thinking back, we had experienced random cylinder mis-fires about five years ago, that changing out the spark plugs did not resolve.   The cure at that time was replacing the electronic ignition control module, mounted on top of the air filter housing on the passenger side fender.  That control module is the object to the right in the photo below.   So, I replaced it again, thinking it might have gone bad again.  No dice.

This miss was now almost constant, with the check engine light and code being set before I could even get out of the driveway.   I replaced the plugs again figuring that even though they still looked good (denso triple electodes), they had a bit of wear and it couldn’t hurt.  The trouble remained, and plug 4 definitely had more carbon build up than the others, which confirmed the misfire.

I reset the codes again, and swapped coil packs (coil pack shown on left in photo above) between cylinders 1 & 4 and noted that the miss continued.   If my hunch was right, that I had a bad coil pack, the new code should be P0301.  I crossed my fingers as I rescanned and waited for the trouble code appear.  P0301.  Success – the problem moved to the #1 cylinder, confirming the failed #4 coil pack.

Another quick trip to the parts store for a replacement coil pack and this one was finally solved.   It’s an odd thing, but the feeling after one of these sessions is a bit like completing a 1000 piece jigsaw puzzle – drinking in that sense of accomplishment, savoring it for a few moments before moving on to the next challenge.

6 Comments leave one →
  1. Tim permalink
    February 3, 2010 3:09 pm

    First Jim, now you. I’m destined for turbo problems next I suppose.

    So how does she drive with a properly working turbo, much less an upgraded one?

  2. February 4, 2010 2:56 am

    Runs well for a solid 4 door. It won’t give you nose bleeds or anything, but it is now much more fun to drive. It’s amazing how much 1 dead cylinder will hamper drivability. Logically, you’d think you would only be down 25%, but the effects are much greater. Glad that’s all solved now…

  3. February 4, 2010 8:56 pm

    glad you got the gerbil back on the wheel.

    how much more power is the K04 supposed to give over the K03?   given how the car used to run, this may not be an easy thing to judge using the butt-dyno.   i’m sure anything feels better than what you were dealing with before.

  4. February 5, 2010 2:04 pm


    I have no benchmark on this. I suspect to really take advantage, I’d need an ECM update / flash to raise the boost. I think stock is 7 PSI or less and output was 150 hp. Pretty much the same motor would put out 200-225 in the TT model, so …

    At what point injectors, new cat back exhaust, different intake ducting / plumbing, etc would need to enter into the equation to begin to really see a difference?

    I suspect it will probably remain as is, and we’ll trade it out in another year or so. If the wife still likes this car line, I’ll see if we can find a newer used S4 with the 2.7 bi-turbo to have a better starting platform to build on. But, she might go another direction totally next time, so who knows…

    Since her other vehicle is more performance oriented anyway…

  5. xolalegenis permalink
    October 5, 2010 5:43 am

    great job, and great documentation.


  1. Audi A4 K04 Turbo upgrade / replacement « markitude

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