Pass SMOG - 1989 911

[AshEvan]

Have a friend with a really nice, well maintained car that recently went in for SMOG test here in CA and failed. She asked if any recomendations could be offered. Might have to replace converter, or could 02 sensor need to be replaced based on results.

Experts please chime in.

[Trog]

NO (PPM): Oxides of nitrogen (more commonly called NOx) are odorless gases that help form smog, and give smog its characteristic brown color. NO is produced when temperatures in the combustion chambers exceed 2500 degrees Fahrenheit. Excessive engine temperatures could be caused by a lean fuel mixture, by retarded timing, by carbon buildup inside the combustion chamber, or a defective engine cooling system.

[dtxscott]

A defective O2 sensor would cause a lean running condition and elevated temps.

I would check the O2 sensor and timing to make sure a clean burn is happening.

Many people advance timing to get a little more top-end power so this may be the case.

[Wilywilly]

I have been told that if you unplug one of your injectors that the car will pass. Runs a little rough though while it's unplugged.

[kidrock]

a lot of info on this if you do a search.

FWIW, there are many things that can contribute to a car not passing inspection. I would do the following first:

1) make sure O2 sensor is operating properly.
2) make sure air/fuel mixture is appropriate (14.7)
3) adjust valves before inspection.
4) run a can of Techron or SeaFoam in a full tank before inspection.
5) probably most importantly, take car for brisk 30 drive before inspection.

All of the above will help immeasurably.

[love911]

There is a program called consumer repair assistance through CA/BAR .If he/she wants to participate he/she can ask for the application from the smog check station or print it from their web site(WWW.smog check.ca.gov).Based upon its report that I see is qualified for $500 free repair money, if the repair bill goes over that amount he/she will pay the difference.As far as the diagnosing the problem goes its most likely due to lean mixture and its clear because the CO&HC have good numbers,the second cause of failure could be the MAF and O2 sensor.Don't let anybody tell you ,that you need to change the catalytic converter,it is in perfect condition based upon the reading that I see and mileage of the car,I have seen porsches with well over 200K miles with original cat that it passed the smog (mine one of them).Good luck.

[ths911]

When I purchased my '90 cab a few years back, it had been owned by a woman who had it 8 years and it barely passed CA smog. The next time I had to get it smogged it passed with flying colors. The difference being - I drove it much harder than she did.

I agree with Kidrock. Do the simple things before getting too deep into repairs and replacing parts.

Does she have a Porsche mechanic she trusts?

[john walker's workshop]

there's certainly room to try and richen it up and still be under max. richer is cooler.

[Noah930]

If she's not too mechanically inclined, she could try taking her car to Tony Callas (whom I believe is down in Torrance) and see if his shop will help her get the car smogged.

[TCallas]

It sounds like this car sat and idled too long (and got too much heat soak) before the smog took place. These cars (84-89 911's) rarely have any issues passing the bi-annual emissions tests.

As per what is considered normal automotive combustion engine emissions, the 2-way catalytic convertor minimizes or oxidizes (burns off) the Hydrocarbons (un-burnt fuel) and Carbon Monoxide (Burnt fuel). The 3-way catalytic convertor is meant to ALSO eliminate or at least minimize the NOx tailpipe emissions (Oxides of Nitrogen). By utilizing the Rhodium coating inside the 3-way catalytic convertor it removes the O2 (Oxygen) from the NOx to turn it back into Nitrogen (N2) again, you cannot oxidize NOx because it is already oxidized.

[stlrj]

High NOx is a sure sign of a tired cat. No matter where you take it, that's the first thing they would replace.

I just had my Chrysler LHS smogged and it did pass. However, the NOx was a getting up there, so the first thing the tech mentioned was my cat was getting tired.

Cheers,

Joe

[Drew001]

Originally Posted by stlrj

High NOx is a sure sign of a tired cat. No matter where you take it, that's the first thing they would replace.

Originally Posted by love911

Don't let anybody tell you ,that you need to change the catalytic converter,it is in perfect condition based upon the reading that I see and mileage of the car,I have seen porsches with well over 200K miles with original cat that it passed the smog (mine one of them).

These opinions seem to conflict - so which one is correct?

I need to get my '87 tested very soon.

[1990C4S]

I agree with love911.

I had a car with really high NOx, everyone said change the cat. It found an open vacuum line and cut my NOx by about 80%. A smoke test on the intake system is cheap and an easy way to find vacuum leaks. Your car is lean, so I think you have a vacuum leak.

Another VERY IMPORTANT issue: does the car have the factory chip? My 89 will not pass emissions with a Steve Wong chip installed, I have to go back to the factory chip to pass the NOx test. In fact Steve suggested I remove it when I told him I failed on NOx.

Also, I would pull the O2 sensor off the car and do the propane torch bench test. If it passes that test re-install it.

The unplugged injector won't work here, your NOx is too high, you are 50% over on the low speed test.

[Quicksilver]

Originally Posted by Noah930

If she's not too mechanically inclined, she could try taking her car to Tony Callas (whom I believe is down in Torrance) and see if his shop will help her get the car smogged.

+1 on this idea unless they aren't inclined to let anyone else work on it (ie Cheap like me!).

[stlrj]

Originally Posted by john walker's workshop

there's certainly room to try and richen it up and still be under max. richer is cooler.

Not if you're lean of peak which is lean of stoichiometric ( 02 sensor range ) as you imply, then it gets hotter when you richen.

[rusnak]

As others have said, I'd try a new O2 sensor first. Also make sure the brown jumper wire next to the DME brain is connected. The factory cat will last a very long time, unlike the ceramic aftermarket cats.

It won't work to try to lean or richen the AFM because once the car reaches operating temp, the system will go into closed loop, and the lambda control will take over, locking out any changes that you may make to the AFM.

If the new O2 sensor does not work, see if you can borrow a known good cat for the test.

P.S.: Also, as O2 sensors age, they send a weaker signal, which causes the mixture to richen, not go lean.

[rusnak]

Just looking at it again....I wonder if there is a vacuum leak? Those really look like lean numbers. If you can borrow an air fuel gauge like an LM-1, that would go a long way toward answering some questions.

[Goth]

Does she drive the car regularly?

If not, it may be old gas. If so: Techron in the old gas and run it all out. Fill with new gas before the retest.

FYI: I bought a C5 Corvette with just under 18K miles on it. The smog numbers where all extremely good with the exception of the NO. The NO was about 4x the average at idle but still passing. I asked the tech what he thought and he said hot engine. I was thinking; The engine should not be that hot as I did this on my lunch hour and only about 5 miles from work (but since it passed I didn't say anything). I also noticed the car pinged under full throttle. After I put a new tank of gas in it, the pinging went away. I have since had the car smogged 3 times and the NO has always been really low and way better than the average.

Hope this helps,

[Goth]

I should have added: After looking at a receipt for new tires the PO had purchased; I realized the PO had only driven the car about 400 miles in the last 2 years of his ownership.

[1990C4S]

Test your O2 sensor, don't just buy one. It's not likely the culprit.