Oh they have a VAG-COM, that's where I learned about it in the first place. But that's what's so frustrating about this problem: the car will breeze through the readiness procedure every time with flying colors. Then the error codes will slowly creep back in over the next day or so as the car is driven normally (usually VERY sedately). And the misfires can strike at any time!

 

Do you ever get the misfires when the car isn't moving? Something that intermittant starts to look like a bad wiring connection to the coil packs or similar that is caused by vibration while driving. My understanding of a "misfiring" code is that the ecu doesn't see the proper voltage/current dynamic from the coil/spark plug - otherwise what would the ecu use to "see" a misfire in the first place? Never had this problem myself, but I've seen enough other wiring problems to be suspicious...
Jim

 

yes, it frequently happens while sitting still and idling. It happened with the previous coil packs (which all tested good) and the brand new coil pack that's been installed as an attempt to rectify the problem. Replacing plugs and plug wires didn't help either.

 

The ECM uses the crankshaft sensor for misfire detection. It measures how long it takes each each cylinder to move a predetermined amount. If there are differences in the amount of time that it should take then misfires will be recorded.
The amount of voltage to the coils has nothing to do with it. If the ecm sees voltage problems at the coils it will flag coil circuit faults.

 

It's interesting that the P0411 code isn't actually documented anywhere in the repair manual. That definition for the error code is the one that VCDS gave me. But I just used a cheap handheld scanner today to read error codes, and it gave me a slightly different definition for that error code:

P0411 - Secondary Air Injection Upstream Flow Detected

That's not the same thing as "flow too low" at all. Upstream flow implies that exhaust is flowing into the SAI injection tube when the combi valve is open, most likely due to excessive exhaust backpressure (higher pressure than the SAI pump can generate).

The mechanic working on my car still hasn't accepted that the catalytic converter is bad. He's thrown all kinds of parts at the engine to try and resolve the misfires (new fuel rails, new injectors, etc) and it still continues to set the engine light after a couple of drive cycles.

 

Sad to see that.

 

Finally got some action on this issue. The mechanic finally saw the light and replaced the catalytic converter. The old catalytic converter was rattling platinum around on the inside. The new cat helped the engine run much better. Logging with the VAG-COM showed that both O2 sensors were finally reading within the same range all the time.

However the engine light still came on very occasionally for random misfires. I finally tracked it down to the fuel pressure regulator. The nib where the vacuum hose hooks up was all mangled and bent, thereby causing an intermittent vacuum leak. I heard it using a mechanic's stethoscope, it was hissing on and off about every 2 seconds. This was causing intermittent and sudden overfueling at idle and light throttle (when vacuum is supposed to restrict the FPR). That's probably what caused the cat to go bad in the first place.

And I thought the engine ran better after the new cat? Wow, now that the FPR is replaced, it's like driving a whole new car! Throttle response is fast, light-throttle driving is buttery smooth, and even the brakes work better (more vacuum for the brake booster). It's amazing how much trouble a silly little vacuum leak can cause.