Hi I have a 99 a6. Just got it and it had about 169k on it. I ran some 3/4 seafoam through a new tank of gas and the other 1/4 through the vacuum brake booster line. So it was a bit sluggish and set off a few obd codes. I then ran some more seafoam through again and then replaced the plugs with a single electrode NGK Iridium plug gapped at .032. So I got all the codes erased. But I still have one saying PO0420 Bank 1 Catalyst Efficiency below threshhold. Is this the first o2 sensor? I thought maybe I broke up alot of carbon and got it contaminated?

 

If you do not do the sea foam treatment correctly, you can foul the O2 sensors. I would clear the faults and drive the vehicle and see what comes back.

 

If it's a catalyst below efficiency code it's either the secondary (after-cat) O2 or the cat itself. Cat efficiency is determined by reading the secondary O2 sensor and comparing it to the primary pre-cat sensor.

 

Ive been using seafoam for years in everything from my lawn mower to my A-6 2.8 30 valve FWD. Nothing better for clearing out the crud if you know what I mean? I can really tell the difference, Have never gotten any codes from using it either. However! I only use it in the gas tank w/91 octane gas. 1 bottle to full tank every 3/4000 miles, And my baby still purs like factory fresh smooth after 10 years. Ive never used it in oil or other applications, but I can swear by it as to keeping the injectors clean and again after 10 years, I still avg. 22 miles per gal in all driving conditions city/highway

 

FWIW: I believe Seafoam recommends a Oil/Filter Change shortly after using it and I thought the they also recommend 1/2 can in Gas Tank - 1/4 can in the Crankcase and a 1/4 can thru the Brake Booster. Not that I think any of that would really matter in your case, I just thought I'd put that out there.

TJ

 

Sorry guys, I should have been more clear. I think Seafoam is great for clearing fuel system gunk and keeping injectors clean and the like, But I never,ever,ever,ever, Put Seafoam in my crankcase. If your using a good synthetic oil to begin with, dont ever put additional additives in it . Total wast of money and time. Good oil needs nothing but to be changed at the sugguested intervals...... sorry

 

Not to shoot you down TJ,,,, I just think Seafoam overreaches with that brakes and oil bit to sell more product.

 

No problem Capt ~ I've been tempted to try it on my 99 Toyota P/U but just haven't worked up the courage yet.