hobbes45

Just failed the smog check! was 173 HC where a maximum of 100 is allow at idle (passed the 2500 rpm test). 95 993. I'm bringing it into the shop tomorrow. What are the possible causes/fixes for this problem? Will a major service fix this? Your help is always appreciated. TIA, Hobbes

jerrykrug

I have heard that you need to run it good and hard prior to the sniffer test, It need to be at full temp. so have a little fun for 10+ min. before the test. good luck

993,951,944

Yes, try getting the engine hot, 20 minutes minimum required. If it fails again, it could
be carbon on the valves, which in most cases,
can be cleaned with "MotorVac". A few P-car
repair shops have this MotorVac system.


All the best,

jz

I just failed smog two days ago on a 96 toyota tacoma. I failed the same part you did. I had 67 HC on a max 54. I changed my dirty air filter, put in a new oxygen sensor, put in high octane with a fuel cleaner and drove it hot all day long before taking it to another shop and I passed with 53 HC on a max 54.


Could your failing the low speed idle be due to oxygen sensors?


I have to take my 96 993 in for a smog in a few days. I want to make sure the techron cleans out the fuel system first though.

jz

Sorry, I think you failed a different part since I failed the 1500 rpm part...

Allen

Seems like I've heard several people say that adding a bottle of Techron can help in case you have failed a smog test...

White Heaven

I also just failed the smog, HC of 173 where 100 is the limit.

I'd love to know if anyone else had the same problem and what they did.

Dealership doesn't have a clue, suggesting investigating at a cost of $500+ with no guarantess- no where does this leave me?

Thanks.

Jim Morton

I have been helping a couple of friends with similar issues on BMW's. From what we have been told / found, the high HC are indictative of the CAT not scrubbing effectively enough.

As people have suggested, the CAT needs to be nice and warmed up to be working well. Good news is that you do not seem very far off as would relate to a CAT being completely bad. We were seeing HC's in the 400's with bad CAT's on 3.5 liter BMW's.

As a start, I would ditto Kim's (Silver Bullett) suggestion. Get things nice and warmed up and have a "pre-test" performed. If things do not clear up, I would likely test/change the O2 sensor as the cheapest, next likely candidate. If there car is not missing or does not have any loss of power, I would suspect the CAT.

Also, you might want to try and work a deal withe local dealer to see if there are any recorded fault codes in the ECU.

A few thoughts ! Sorry to hear about the problem. Usually these Motronic cars run real clean !

Jim Morton
'95 C2
<img src="graemlins/xyxwave.gif" border="0" alt="[bigbye]" />

911

I just had a smog check done on the C4S I purchased yesterday. However, although the car passed the Emissions Test, it failed the Functional Check.

I just had the Wiring Harness done a few hours before the smog check. Could that have affected the smog check?

Does anyone here have any experience with this? Thanks.

Lorenfb

There appears to be a number of issues with
regard to a smog test in CA:

1. For cars with OBDII, the car must have all
its "flag" up, i.e. the DME must not have
been recently reset and some mileage cycling
has to be done to allow any fault codes to
re-appear.

2. The HC issue is more related to other areas
other than the O2 sensor, unless the HCs are
way out. So don't waste money on an O2 sensor
if the number is close.

3. I've worked with a number of Porsche shops
where the secondary air causes a smog test
failure. This results from the air injection
being plugged with carbon. Not a simple fix.

Check out the web site, Systemsc.com, under
Diagnostics. It may have some helpful info.

Good luck
Loren
'88 3.2

Steve Weiner-Rennsport Systems

Hi:

Some good information here,......

I'd just add that one MUST get the engine good and hot before doing the smog check. Further, high HC's can be caused by valves not sealing real well in an otherwise healthy engine, and a good dose of very spirited driving (+75 miles) with a large bottle of Techron on the tank really helps.

For "problem children" cars that have spent too much time idling in traffic, the MotorVac process might be the ticket. Techron does the same thing, albeit much slower.

Lastly, OBD-II cars must be driven continously for a minimum of 30 minutes (perferably more), before the smog test to clear the ECU's readiness codes.

chris walrod

I have been told to get the car good and hot (like others have said), get the car tested on a low tank of fuel. This maximizes the vapor scrubbing by the charcoal canister.

For 2wd cars, inflate the driven tires to max pressures to minimize the effects of the dynamic loading.

If possible, do the smog check on fresh engine oil.

I absolutely hate smogging cars. I dread it almost as much as going to the dentist (which I have to do tomorrow)

Hope this helps.

Pete Lech

At my last smog check a few months ago, my HC was hardly measureable. Having recently done 3 20-minute practice sessions of continuous laps at an autocross must have been the "Italian Tuneup" the car needed. Lots of fun too.

I did make sure the car was thoroughly warmed up also, but otherwise no other special preparations.

ebaker

If the HC is high and there is no mis-fire then the mixture is probably too rich. Wouldn't adding some alcohol to the mixture lean it out?
Fuel in high pollution counties of Texas has 6% oxygenate (alcohol) added. Since alcohol contains 1/2 the energy of gasoline all cars run 3% leaner. This should reduce HC on cars running rich.
You can also try running it hard to burn any carbon off the plugs and catalyst.

911

Fyi on my Smog problems. Just as Steve W. had mentioned, my ECU did have the ready codes erased due to the battery being disconnected for the Wiring Harness recall. Therefore, I had to have these codes set to "readiness" status.

The car had to go through a series of RPM & time tests at the dealer (ex: 1800 rpm for 6 minutes, etc). This was done at Pacific Porsche here in Torrance. The test went well and my car passed the smog check w/o a hitch that same day.

Rich