P0299 amongst other things

**MurkyRivers_A4** · 01-30-2016 07:18 PM

OK so I finally got around to picking up another A4, this time a 2003 TQM as opposed to the 2002 that I had. I just picked it up a week ago and I have had some irritating issues:

Diverted valve leaking
Heated stock Springs
Hideous wing
Faux carbon fiber interior trim
And a bunch of non sense Honda type things on the interior, including some unknown weed roaches in the rear ash tray

None of those were a big concern when I bought the car since I knew they would all be relatively easy fixes. I didn't have my scanner on me when I picked the car up but when I got her home I checked it. Turns out it is a P0299, turbo charger underboost which is something I've never seen before.

So I dig into that code and start looking for boost leaks. Replacedo any questionable check valves with kynar ones from my last purchase, and double checked the SJP, as well as everything else, for any potential leaks. Tightened all intercooler tbolt clamps and it would appear to be rock solid. I replaced the N75 with a known good one from my last A4, as well as bypassed the N249 to eliminate that as a potential cause.

After all that I'm still having the same low boost problem. It felt extremely underpowered so I decided to temporarily hook up my innovate boost gauge and it turns out I'm maxing at 9 psi, which would be fine for stock, but the boost is fluctuating from 6 to 9psi and you can hear the turbo whistling up and down which isn't normal.

Now, in my time checking all of the check valves and vacuum lines, I noticed that my injectors looked different compared to my last ones. These were a light blue as opposed to the dark blue. I researched the part number on the side and it turns out they are the TT 386cc injectors. This would leave me to believe that the car has a 1+ tune at a minimum. So I did some more research and checked to see if it was an APR tune by way of cruise control lever manipulation. While holding the reset button the CEL does flash but only once and not once then off and then once then off, it stays on then blinks off one time then stays on again. Doesn't seem like the APR program switching sequence. Now, if it is a stage 1+, shouldn't I be seeing more than 9 pounds of boost and what is causing the fluctuations? I'm thinking clogged cat but can't be too sure, however, the exhaust pressure form the tail pipes seems very little then what I'm used to seeing.

Any help is appreciated.

**customa4** · 01-30-2016 08:31 PM

How many miles on it? Clogged cat is a likely possibility. The car must be tuned to be running those injectors or it would run like crap and you would have more than just an underboost code. Only other thing I would think to check is that the wastegate isn't the problem. I'd probably inspect the cat even if you find something that leads you to believe there's a problem with the turbo. I've got my money on the cat. When mine was badly clogged it would only boost 9 psi even with an APR big injector tune. Here's my thread. Click

**MurkyRivers_A4** · 01-30-2016 09:15 PM

The car only has 109k miles but the PO said the timing belt broke and had the head rebuilt. Had records to show all work and I compared the VIN on the paperwork to make sure all was accurate. I'm assuming the owner prior to him performed all the mods since the kid I picked it up from had no idea what was done to the car.

I did inspect the turbo and it had very minimal shaft play. I'm leaning towards the cat as well since the exhaust pressure is very weak and the amount that is coming out is extremely hot. I checked the cat and turbo after a spirited run, in the garage with lights off, and couldn't see any glowing red parts.

I may just pull the cat and see how it looks. If it looks anything like yours, I would say that's my problem lol.

**MurkyRivers_A4** · 01-31-2016 11:06 AM

Was definitely the catalytic converter. I started to remove it to check the waste gate flapper and the front side of the cat, closest to the turbo, looked completely fine although there were some marks that would indicate the catalyst was sliding backwards and is loose.

So I decided to take the whole cat out and inspect it. Not to my surprise, the back end of the catalyst had come completely loose and lodged itself against the o2 sensor. Since I didn't have a spare cat, or test pipe anymore since I gave that to my friend, I had to spend 3 hours with a screwdriver, crow bar, hammer, and pliers gutting the cat.

While it was off I took the opportunity to inspect the turbo and waste gate flapper and all was well. Installed the gutted cat back in place and all the power has returned. Thanks for the advice and I'm glad it's better, now just to hunt for a new cat.

**customa4** · 01-31-2016 11:09 AM

Awesome news man. Gotta love when a diagnosis goes that easily. Seems like you were on the right track from the start. I'd recommend a 034 HFC, I've enjoyed mine. I'm surprised your cat was junk with that low of mileage.

**MurkyRivers_A4** · 01-31-2016 11:51 AM

Yeah, I did a lot of research before posting, as I normally do, but after ending up with no positive results I had to see if anyone else had any suggestions. I'm glad I did lol.

Something tells me this isn't the original cat. I'm assuming it a test pipe and some point in time, probably when sold to the PO. There is no CEL from the rear o2 so that must be programmed out with the tune as well.

**MurkyRivers_A4** · 02-01-2016 08:42 AM

To close out this thread, I am adding a picture of the dreaded catalytic converter. Hopefully this will help future members if they come across the same issues I had.

Remember, the front side of the cat looked completely fine so you cant base the condition of the car by just separating from the turbo, you need to remove the whole thing and check the back end.