When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Need a little assistance. Up for the 2 year smog and my 993 failed for high HC and CO at 25mph dyno pull. Passed both idle and 15mph. Last few times no issues and highly doubt its the cats as I swap the fabspeed cats for the stock ones to pass visual, then put the fabspeed cats back once it's passed. After I put the stock ones one I drove sunrise highway to get them good and hot, then straight to the smog shop. I've attached a durametric log with all readings enabled driving around my neighborhood for a bit. O2 sensor on one bank is very different than the other however I saw there was a bug regarding durametric readings in another post with respect to O2 readings. Not sure if that's still the case, using the latest downloadable usb version. Any advise is muchly appreciated. TIA
Did you make sure the car was driven and pretty hot before going in for smog? I know it sounds silly, but that helps tremendously- I know you said you drove it, but sometimes you reaaaally gotta drive it.
If the CAT is working it should be much hotter than the mufflers after a good drive, like a couple hundred degrees F if I remember correctly.
could be a quick check.
The Durametric bug was addressed a while ago and if you are using the latest download software and are not seeing any reported OBD codes that do not exist for our cars you are good to go. The problem was related to communication errors between Durametric and the Motronic ECU that threw all sorts of erroneous codes including ones related to the oxygen sensors.
Then by looking at the running data graph in Durametric for the oxygen sensor and a little internet or Renlist posting research on what the signal pattern should look like you may be able to identify if there is a faulty oxygen sensor.
If this turns out to be beyond your capability to diagnose replacing any that are original to your car is a good shade tree option. If you buy the sensors in a Bosch box, not at the dealer and put them in yourself it is not expensive, $60-$80, or difficult: https://993servicerepair.blogspot.co...anagement.html
Finally, you may have a fouled fuel injector, Before taking the car in to investigate this I would run two consecutive tanks of gas with Techron added to clean things out.
If after doing the above and having a pre-test done you still have problems, it may be time to involve a professional who can do a more comprehensive diagnosis.
Having gone through this in the past with similar results (High HC), I followed some advice given to me by Steve Weiner. Order some Jectron and Ventil Sauber. Before you fill up, pour the cocktail into your tank, fill the tank up and start driving and let the fluids run their course.
My HC values on the follow-up second test dropped dramatically.
Apparently, the "Naphtha (petroleum), hydrodesulfurized heavy" in the Liqui Moly product cleans the Catalytic Converter
"Hydroconversion
Mohamed A. Fahim, ... Amal Elkilani, in Fundamentals of Petroleum Refining, 2010
7.2.7.1 Naphtha Hydrotreating
Heavy naphtha hydrotreating is usually used to remove the impurities so that the hydrotreated naphtha can be introduced to the catalytic reformer. The expensive platinum-based catalyst used in the reformer is sensitive to poisoning by such impurities. ."
It could be as simple as a sticky/dirty injector resulting in poor combustion and unburned fuel in one of the cylinders in that bank. Techron or the Weiner cocktail mentioned above may very well do the trick.
The trick I have used is E85. Run the tank low and mix about 4 gallons of E85. It burns really clean. My car with 136000 miles and not been opened passes with flying colors. Make sure after the test you burn that all out of the system as E85 is not good on rubber lines. I’ve done this for the past 3 inspections. As others have said, the car needs to be hot. That can be a challenge in January.
Thanks everyone, have a few things to try. Cocktail is on order. Forgot to mention, had a full engine rebuild 30k miles ago at 122k. Cat's were nice and hot for the smog, also unless the stock catalytic convertors can get contaminated sitting in the garage I'd be surprised that was culprit as they only get swapped on for smog only. Readiness monitors are never a problem any more.
You are running rich and that's probably because of your RS Cams. That's why you will pass at idle, but not at higher RPMs. I would run a 50% mix of E85 and gas to lean out your AFR's.
I think the technician can make a difference as well, by making sure the car stays hot and having a steady throttle foot. I've had cars that failed pass by changing nothing but who was doing the test.
Having gone through this in the past with similar results (High HC), I followed some advice given to me by Steve Weiner. Order some Jectron and Ventil Sauber. Before you fill up, pour the cocktail into your tank, fill the tank up and start driving and let the fluids run their course.
My HC values on the follow-up second test dropped dramatically.
I too have the high HC fail on my recent smog test. After doing the cocktail, did you drive the car until the cocktail in the tank was used up and then refill with regular gas before smog test? Or did you smog it while the cocktail still in the tank?
Thanks.
Harold
01-23-2021, 06:00 PM
CA Smog Fail
any more.
