c2ss

So the dreaded biennial smog test time came, and my car got a fail. 1998 C2s with 74K miles. Appears to be failing due to high level of hydrocarbons.
Last smog check was in 2015, and it passed.

For the current test, I drove the car approximately 10-15 miles with a mixture of back road and freeway driving. After the first test run, the HC was off the chart. Took the car for another 15 mile freeway drive, and then back for a second smog test run. HCs have improved somewhat, but still a fail. The rest of the indicators seemed to be OK. Standing behind the car, I could hear some pinging during the test, during 2nd gear acceleration at lower RPM.

What's interesting, is that 2 years ago HC readings were substantially lower. Car has been driven only a few hundred miles in the past 2 years. Smog tech suggested that either the gas in the tank is bad or the cat is on the way out.

2017 TEST 1 - FAIL
HC MAX AVE MEA
15mph 54 9 100
25mph 37 6 32
-------------------------------
2017 TEST 2 - FAIL
HC MAX AVE MEA
15mph 54 9 67
25mph 37 6 29
----------------------------------
2015 TEST - PASS
HC MAX AVE MEA
15mph 54 9 12
25mph 37 6 5

So I took the car for a 40 mile drive, burned the old gas, filled it up with a 100 octane, and went to another smog station (same one I used 2 years ago). The tech, after monitoring a pretest run, stated that the HC kept spiking up and down. He suggested that either the cat or the oxygen sensors are bad. There are no CELs though.

Due to the cost of replacement cat and O2 sensors, I decided to do address some other items first: changed distributor caps and rotors (Bosch), replaced all spark plugs (Beru), did oil change (Motul 300V) and cleaned the cone air filter. Took the car back for a pre-test, and the tech said the same thing: HC reading are all over the place.

I did some searching on RL and Pelican forums, but did not find any concrete solution for high HC in 993s. Since there no CELs related to cat or O2 sensors, what else can cause this high HC issue? The cost of the replacement cat is astronomical Should I replace O2 sensors first?

Any advice and input would be much appreciated.

Al.

c2ss

test 1

c2ss

test 2

c2ss

2015 test

MarinS4

Change your oil. Cycle through a couple tanks of fuel. Drive the car very hard to get the cats nice and hot. Take in for smog when the cats are really hot.

You're really pretty close. I'd be really surprised if working the cats does not get you a pass. They just need to be woke up from sitting IMHO.

Ash

I had high HC at a previous smog check. Drive the car until you get close to an empty tank. Get a can of Lubrimoly Ventil Sauber and Jectron and pour it into the tank then fill up. Cycle through enough of the tank of gas (around 100 mile drive or more) and then go for your smog check.

My HC count dropped substantially. I actually did this on a second smog check after fail due to me forgetting that the battery had been disconnected briefly so no readiness codes. My HC's were borderline so I decided to do the cocktail above anyways while resetting codes. HC's again dropped on the second test.

Credit for this goes to Steve Weiner

Steve Weiner-Rennsport Systems

Did you change plug wires at 74K when you did the caps, rotors, & plugs?

If they are original, they are LONG overdue for replacement!!!!

shadow993

This is most likely the culprit...

nine9six

Because of how close you are on your hydrocarbons, I would go ahead with the cocktail mentioned and get things good and hot prior to retest

This will buy you time to have your plug wires replaced if that is indeed the culprit.

Also, make sure your oil level is on the low side. If oil is being ingested through the SAI system due to a bad check valve, then that would explain the high hydrocarbons as well.

If you have a good generic OBD2 reader, I would hook that up to see how your O2 sensors are behaving.

I do the aforementioned cocktail every year just prior to oil change; my CA smog test always look great.

kb

Same exact scenario happened to me in Virginia. 2015 - car passed with low hc readings so I was baffled. Checked plugs, wires and did bg44k cocktail and failed a second time. This was my fix. Replace your air filter with porsche part and replace or tighten your belts. Finally make sure testing garage does smog in 1st and/or 2nd gear only. Tester kept shifting to 3rd gear because he thought rev was too high. After I instructed him car passed with very low hc reading. At least for next 2 years. Good luck. Hope you get same results I did.

Gbos1

So glad I don't have any Emissions Testing in the State / County I am in! What a PITA! My mechanic was telling me he had another 993 and was trying to get the readiness codes for Emissions testing and had to drive around the whole day with no luck under so many RPM and speed or what ever. Followed Porsche's procedure and everything ...eventually he got it to work the next day

c2ss

Thanks to everybody for replying. I really appreciate the advice.

Ordered the Valve Clean and Jectron, tank is almost empty, so will try it as soon as the "cocktail" arrives and will post results.

Fresh oil change before the 3rd pre-test run, will try the cocktail suggested above and cycle through a tank of gas

I did not change the wires during my ownership. It is unknown whether the plug wire were ever changed, visually they seemed to be in pretty good condition with no damage and just minor spiderweb cracks around the bends . I ordered a new set of Beru wires on your advice, I'm sure it will not hurt:-)

Dipstick reads in the top 1/4 of the "twisted" portion...perhaps I should drain some oil?
Will do the cocktail and wires, hope that helps...if not, I guess then to the OBD2 reader and o2 sensors. I'm really hoping for the magic cocktail to work though :-)

They tested in 1st and 2nd only. One of the prior owners installed a cone intake, so I don't have the original part. I was planning to go back to the OEM airbox and have been looking for cheap used one online for a while, might have to speed that process up.

911F1

Bumping this thread. It would've been nice if the OP followed up with his result.
My HC levels are very similar to the OPs. I'm wondering how the cocktail worked out.
Do people suggest testing the car with the cocktail still in the tank? Or should I run
it completely dry then fill up a fresh new tank of gas?

doublecabmel

good old CA

Mr.Woolery

The simple stuff to lower HC's

-The "cocktail" in your tank after the old fuel has been used
-Do an "italian tune up" driving it around trying to keep the cruising RPM's above 3k
-Instead of using 100 octane gas, if your state has an ethanol mix gas, get a premium ethanol gas (something with 15% ethanol in it to lower your HC's).
-Ensure your car isn't overfilled with oil.
-Change your oil, oil filters, and air filters.
-If you still have a dual mass flywheel-try running your AC on low while getting the smog test done. This helps to stabilize timing for DMF's that are wearing out and allowing timing to wander (bad for HC's).


The more expensive stuff to lower HC's
-Replace plug wires
-O2 sensor(s)

The even more expensive stuff to try:
-Replace your cat


Does your car throw any codes?