Richard S

Well, call an end to global warming, my car passed smog after failing miserably two times.

Here the details...87 S4 5-spd, Devek Level II headers, RRFPR, High-Flow cats (Random Technology?). It had a little problem passing in Dec 2005 when I bought it, but the PO had Devek get it to pass before I purchased it. So I kinda expected it to be on the fence. The car always had a slight stumble at idle, and would occasionally pop/backfire when letting off the gas. And there was a strange rattle from the exhaust sometimes.....

First test results

Speed.....15mph.....25mph
RPM........1260........2036
HC..........252..........127.........FAIL.....Max allowed 108 and 83
CO..........0.55.........0.56........OK, but near the upper limit.......Max allowed 0.71 and 0.58
NO.........2091.........894.........FAIL, Gross Polluter.....Max allowed 767 and 706

Yikes, something seriously wrong. So I did the basics, like search Rennlist of course. I also changed the spark plugs to stock copper pugs, one step colder (old ones were 4-prong, only 1 was discolored), installed a new fuel filter, fixed a vacuum leak, checked O2 sensor (works fine). Went in for the second test.

Second test results

Speed.....15mph.....25mph
RPM........1254........2085
HC..........254..........119.........FAIL.....Max allowed 108 and 83
CO..........0.53.........0.49........OK.......Max allowed 0.71 and 0.58
NO.........1676.........835.........FAIL, (now below gross polluter level).....Max allowed 767 and 706

Still bad. No change in HC, NO fell 20% at 15mph and 6.6% at 25mph. So I pulled off the exhaust, and found the high-flow cats were now no-flow cats. The ceramic material had broken apart and was blown down the exhast to the first muffler.....must have been source of exhaust rattle. I shook the loose stuff out, now the cats are simply open pipes. I then installed a different exhaust, one with stock S4 cats modified to fit to the Level II headers. I also checked the fuel pressure. It was set high at 72, so I reset it to 55. Still had a slight stumble, so I checked the MAF. The wiring looked bad, so I bought a new connector and re-wired the harness.



After this, it still had a stumble, so I swapped in a different MAF. Now it was running nice and smooth. So I went for the third test.

Third test results

Speed.....15mph.....25mph
RPM........1235........2035
HC............69............34.........PASS.....Max allowed 108 and 83
CO..........0.10.........0.11........OK.......Max allowed 0.71 and 0.58
NO...........189...........85.........PASS...Max allowed 767 and 706

Woo Hoo I passed! The Earth is now safe, it's already colder here! Wow, big change in numbers....HC down approx 72%, CO down approx 80%, and NO down approx 90%.

In the interest of science I could have taken each step one at a time (cats, wiring, MAF) to determine the actual cause/cure, but I only have 1 week to renew the tags, so I had to get it done now. From reading many past threads, I'm leaning toward re-wired and different MAF as being the main solution. I suppose I could re-test for fun after I put the old exhaust back on, and see the effect of cats-vs.-no cats. But for now I'm just glad to pass and get things working right.

Rich

ZEUS+

Glad that you passed. The maf wiring was a definite time bomb. Surprised that the CO was not higher and NOX lower with fuel pressure so high. Good job !

jorj7

Rich,

Glad you found the problem. Even though it's a pain to do this smog stuff every other year,
it looks like you cleaned up a few issues with the car,

Jim bailey - 928 International

That is not unusual for the aftermarket high flow cats to fall apart inside especially if the car is running way rich and putting a lot of unburned fuel into the cats.

Nicole

It's "Global Climate Change", Rich. Not all areas are supposed to get warmer... Sacramento and the surrounding areas, for example, will be freezing (or friggin') cold all year round.

Bret928

So Rich, hows it feel on the road now after all those changes? I'd bet it even she even feels better too.

Ian S4

Sorry for being such a pedant, Richard, but your car is likely putting more CO2 into the atmosphere than it did before the repairs! After all, the job of the cat is to convert HC and CO to CO2 and H2O.

ZEUS+

I thought he did test with S4 cats. High CO2 is an indication of efficient combustion and is basically for diagnostics. Does Cal. fail for high CO2 ?

Ian S4

Not yet, but they will if Arnie gets his way....

Bill51sdr

Next step is to ban all internal combustion pwered vehicles, but that is a topic for another forum...

No, you do not fail for any kind of CO2 enission... yet.

Richard S

The car runs nice and smooooooooth now. Except for the rear belly pan touching and vibrating on the stock S4 cats. The flange to mate them to the headers puts them in a slightly different position vs. stock, so the belly pan vibrates up through the floor. The regular exhaust goes back on this weekend, so after that I can really get a good feel for things. Throttle response seems much much better now.

Enjoy the clean air for a couple more days....the empty cats are going back on Just in time for the track day!

Rich

Edgy01

Congratulations! Been a gross polluter many times! On one of my cars when I moved back to California in 2001 it NEARLY passed the first time and then we started doing some work on it. Discovered that the catalytic convert was toast,--nothing inside any longer,--burned out. Put on new cats. Next numbers were WORSE than with the burned out cats! I just don't get it!

Buy a diesel!