Jerry Garwick

My '91 C2 failed its California smog. At idle the HC reading was 128 versus allowable of 120. At 2500 rpm HC was 37 versus allowable of 140. Measurable CO2 was 13.90 at both rpms. My mechanic speculated, based on "low" CO2 reading and high idle HC that the cat is bad. The car has 132,000 miles. An internet site sez that sometimes a failing cat can be cleaned by running the car under load and getting it really hot. Does anyone have experience in such things?

garrett376

My readings:
idle HC: 48
2500 HC: 12

idle/2500 CO2: 15 and 15.1

I'd say if your car runs well, no smoking (black) on acceleration, no check engine light, then a new cat is in order.

http://members.aol.com/SportsCarConvert/Porsche.html

Jerry Garwick

Thanks Garrett376. Your readings agree with my two mechanics. Car runs great with no smoke. I wonder if there is any difference between a 380 dollar cat and one that costs 1500 bucks?

kgorman

maybe just a bad O2 sensor?

garrett376

Well, they say you'll get your money back if not satisfied... not bad!

But then a check engine light, and/or bad running would occur...

Cupcar

I had exactly the same thing happen to me in 1999, my car had less than 20,000 miles on it.

I was blown away and didn't know what to do so I changed the oil, changed the o2 sensor and the spark plugs then went back for a re-test.

At the second retest I was lucky and drove the car directly into the test bay with no waiting. I left the car running to keep the Cat hot and.....the car passed.

The first test the car sat parked for 45 minutes before the test and then was started and tested without much warm up.

I think the critical thing I did on the second test is keep the Cat hot. I had a primary muffler bypass at the time and I think that it takes longer for the Cat to warm up without the primary muffler. I don't think any of the other changes plugs, o2 sensor etc were important.

Subsequent CA testing cycles using the strategy of keeping the Cat hot have worked.

Cupcar

One other note, before the second test I made sure the car was really hot by running it hard on the drive to the test center.

Hambisa

At the recommendation of my P-car specialist, I have always had my Porsches tested at a nearby test station that is very familiar with doing Porsches. After they pull it into the bay, they set the accelerator and run it long enough to get all component temperatures hot before beginning the test cycle. (Of course they know not to put a C4 on the treadmill, too!)
Results of my test a month ago, at 142,400 miles with stock equipment, were:
Idle / 2500 HC: 10/10 (max allowed 120/140)
Idle / 2500 CO: 0.00 / 0.03 (max allowed 1.00/1.00)
See if your specialist or OPC will recommend a test station that they use for their smog checks - it can make all the difference between sailing through or hassling with unnecessary repairs and adjustments for re-testing.

Jerry Garwick

Guys

Thanks for the comparative readings and advise. My Porsche mechanic is giving it a quick check to see if has some major problem. I would be surprised since there is no check engine light and it's running great. If no big issues come up, I'm going to run the tank of "old" gas through it, which has been standing all winter, drive the snot out of it, and take it back for a "hot" smog retest. I'll post the results.

Richard Curtis

won't a bad O2 sensor set a code?

Jerry Garwick

The continuing saga just came in from my mechanic. He said that one of my plugs (didn't ask which one) was misfiring. He does not now think the cat is the problem. He is closing shop for the night and will trouble shoot the culprit in the morning.

Jerry Garwick

Let me put this thing to bed. My primary plugs had oil seep into them after the winters long sleep. The car appeared to me to be running great, but was obviously not firing as cleaning as well as it should have. The plug wires were throughly cleaned and the car analyzed, and passed smog. My cat is apparently wearing out, but does not require replacing at this time. Thanks for the help.