Failed Smog Check

[Tompickett]

I took my 1988 3.2 Carrera over for a smog check today, failed, and I am suspicious of the results. On a pre-test I got HC and CO readings of:

HC (PPM) CO (%)
MAX AVE MEAS MAX AVE MEAS
85 28 20 0.54 0.12 0.09 15 mph
67 23 9 0.45 0.10 0.14 25 mph

All of which pass with flying colors. Then they immediately did an official test and I got this:

HC (PPM) CO (%)
MAX AVE MEAS MAX AVE MEAS
85 28 .85 0.54 0.12 2.18 15 mph
67 23 16 0.45 0.10 0.13 25 mph

Anyone have any idea what might cause this??? I mean from 0.09 to 2.18 and what is with the .85 reading in Hydro Carbons?
I am really not sure what to think about this...

Tom Pickett

[911Freak]

Lots of good threads on Carrera failed smog

This was at a "test only" station, right?

Something fishy if the tech "immediately" tested it without any time lapsing between the tests and not tweaking anything in the car... what was the explanation from the tech?

Did you run the car hard and hot as you went in for the test? What were the conditions of the car? Tuned up, daily driven vs stored weekend driver etc.

Did the Tech adjust anything between the two tests? How much time between the 2 tests?

More info needed

[Tompickett]

There was a couple of minutes between the tests during which time the car ideled. Temp was toward the high side of normal, the car had been run for about 30 mins before the first test. ambient temps were near 80 f.

He had no time to tweak anything and yes it was a test only station which I have gone to for several years. The car itself is driven occasionally on the street but mostly on the track. When on track it uses a bypass, and a Wong chip, a Cup sport air intake with a K&N filter.

On the street it had an OEM chip, catalytic converter, stock intake and filter.

The tech said he tested immediately after the pre-test because the car was very clean on the pre-test, and he was surprised at the result afterward--said he had not seen that before. He suggested that perhaps there was a problem with the O2 sensor, or the Mass Air Sensor...

[hcoles]

Considering the HC (ppm) number went from 20 to 0.85 in a matter of minutes and then back to a more expected reading, I propose something went wrong with the test machine.

This appeared to happen when the failed value went from 0.09 to 2.18, please post if you have record of values similar to this.

Have others seen 0.85 ppm in the HC ppm data location. 0.85 may not even be a reading the machine can correctly measure.

[86 911 Targa]

Here's a thought.

If you have the 210F aftermarket thermostat:

Pull the oil cooler fan relay, drive the car, get the temp up to 230ish and try again.

This has worked for me.

Good luck,

Gerry

[Tompickett]

I have not seen values like that before on my car, not the 2.18 or .85...
It has always been quite clean since I rebuilt it 3 years ago...

[Tompickett]

I took the car back over and had it tested this morning. Results were the same as the pre-test, and it passed with flying colors. The tech suggests that perhaps something didn't work momentarily he suggests the fuel regulator, but he figures something mechanical didn't work for 100 seconds and then started working again.

Test results this morning:
HC (PPM) CO (%)
MAX AVE MEAS MAX AVE MEAS
85 28 20 0.54 0.12 0.09 15 mph
67 23 9 0.45 0.10 0.14 25 mph

So I am left to figure out what happened...

[kevin-ct]

Possible a misfire on one of the cylinders? from heat?

[Tompickett]

It was running real smooth prior to testing, but then again it was running on an OEM chip and it is a 3.4 l engine that runs on a Wong chip normally...