imhighlander

Howdy, all. Our 2004 986.2 S recently failed emissions for high hydrocarbons. I'm just beginning to learn about fuel trims, and I have a lot to learn. I'm hoping that as ever, this excellent forum can shortcut my learning a little.
Below are the screenshots from this morning on the Boxster. Clearly the RKAT reading for bank 2 is wonky, but I'm not sure how to interpret it. The car seems to run well and pull strong. It does have a strong exhaust smell I'm trying to track down, suspecting a leak at an exhaust manifold considering how strong the smell is in the cabin.

I replaced the MAF, primarily because all signs indicated it was the original part and the car has 123,500 miles on it. I replaced the air filter while I was in there. The O2 sensors are only about a year old; I replaced those when I had to replace my original headers due to a failed/clogged catalytic converter.

On my handheld (non-Durametric) code reader, it indicated long term fuel trim was at 3.9% for both banks. The screenshots below are from the Durametric. The values stayed within this range from idle to 3500 RPM.

Any tips for where to look next? Thanks in advance.

Tagging my friend Skip @Porschetech3 in case you have some thoughts since you've been valuable in my 996.2 journey as well.

Porschetech3

It's interesting that you failed Smog test but have no CEL or fault codes...... So please post up the Smog test details to indicate just how high the HC is, is it just barely out of the acceptable range?

Secondly your fuel trims are fine......forget about them being the cause....+/- 6% for RKAT is the adjustable range...I start to get concerned at +/- 3% but yours is 1.45% bank 2 and 1.03% bank 1. so no worries...

The headers on the 2004 Boxster contain the pre-cats, but the main cats are further down the exhaust and at 123K are suspect to be inefficient.....The ZDDP was removed from engine oils to guarantee that the Federal mandate of 120K miles of cats were reached ( previous Federal mandate was only 80k miles) ..

But without a 4 gas exhaust analyser you will have to return to the Smog test to see if changing the cats reduces the HC below the acceptable level....

Before changing the cats I would suggest doing the blow-by test to see if the engine ring seal is healthy. A low blow-by number makes it easier for the cats to burn the HC and get down below the acceptable HC value...See this thread for blow-by test ..https://rennlist.com/forums/996-foru...w-by-test.html


Edit :: Also take the car out and run it very hard at high temperature to burn-off /clean the cats, it may be just enough to Pass Smog if you are just a little high on HC emissions..

tcora

Does CO do a tailpipe sniff, or is the emissions test done simply by plugging in to the OBD2?

imhighlander

Here's the printout from the test: HC came in at 0.9657 GPM on a limit of 0.600.

The state has an OBDII reader they plug into the vehicle and I think in some cases, they do a sniff test also. My wife took it in so I don't know for sure what they did. Looks like they had it on the dyno since there's speed data on there.

imhighlander

Also, just as I tell my friend to whom I sold my Pano turbo, I tell my wife to run the car hard. I guess if you want something done right... 😉