1982 911 Emission control failure

[3babiessail]

1982 911 SC Emission control problem.

I just aquired the car and it failed the emissions test ( but fine everywhere else). CO at 1.8% (vs 1.4 passrate, HC at 400ppm vs 250 (passrate) ,Nox 8000 vs 4100 (passrate).

Where do I start looking ?, O2 sensor, frequency valve, control module or elsewhere?

What sort of failure will give this pattern of failing all 3. History from past tests suggests metlevels recently but engine been out since .

[Groesbeck Hurricane]

Where are you located? What emissions levels are you trying to meet?

Check that the 02 sensor is connected. Make sure you are not running the CIS too rich. Do a search on Emission and you will find many who have been down the same road. These cars can pass tests, but it might take some adjustments and parts replacement. Diagnose, then replace.

[3babiessail]

Thanks , I'll do that. There is a suggestion the CAT needs replacing, any idea how I verify that this is really needed ?

[3babiessail]

Thanks, thats helpful. There is a suggestion that the CAT needs replacement, any idea how I could verify this is the right thing to do as it's an expensive part ?

[johnsjmc]

As all three gases are high it could indicate a worn out convertor. Before you replace it have the CO set.I think it is adjustable even on CIS models with an O2 sensor . A good shop can test the O2 sensor ( which is often disconnected) as well as take a sample of exhaust ahead of and behind the convertor to verify it,s functioning. I think you need a convertor but there are lots of owners who have been able to get a pass even without it. A universal type high flow convertor can be welded in to replace yours for much less than OEM.

[mikester]

Did you have the car running at operating tempurature? I the cat is cold then it isn't doing it's job, it has to be at operating temp.

[stlrj]

Before you get a cat, have your CO adjusted and that should take care of your HC too. Next, get a pretest to see if it will pass.

By the way, even a bad spark plug could elevate all three gasses. Might want to look into that too.

Meanwhile, give your wallet a rest. I've been through this many times and it's usually something simple and basic anyway.

Cheers,

Joe

[Lorenfb]

If the Lambda system (O2, Lambda unit, & freq valve) is working properly,
the CO & HC should easily pass assuming the mixture is not excessively rich.
The CAT & ignition timing will most significantly affect the NOx.

Check out this web site (www.systemsc.com) on the Diagnotics (Poor Running) page,
& the Problems (Emissions Failures) page for some additional info.

[stlrj]

should easily pass assuming the mixture is not excessively rich

I'd say at 1.8% CO, the mix is excessively rich since it's after the cat. where they usually put the probe.

Before the cat it should read 0.4-0.8% according to specs. so after the cat should be nothing but clean air...

Joe

[dvkk]

Your NOx reading of 8000 is really high. This indicates to me that it may have been running really hot. A really hot engine can make the CO go up since hotter air is less dense and contains less O2.
How hot was it? Ambient temp?

[stlrj]

Excessively rich mixtures will overheat the cat and even cause it to glow.

Now that's hot!

[johnsjmc]

An excessive rich mixture will also tend to reduce nox as it tends to cool the combustion process in the cylinder Granted it(rich)will overheat a cat leading to a premature catalyst failure.A misfiring spark plug can ruin a cat in as little as a tank of fuel. I still think the cat is probably ruined.The key indicator is all 3 gases being very high,If CO and HC were high and the cat was working then NOx would normally be closer to a pass .If the front section of the cat is working it will "strip" the oxygen from the NOx and then the rear section will "add"it to the CO and HC resulting in their reduction to CO2 andH2O.

[GSpreeman]

Hey, I just failed my emissions test. The only thing that I flunked was NOx. The standard here in NJ is 1378 and I had an actual reading of 1536.

Any ideas of where I start to fix/replace?

[johnsjmc]

High NOx alone is caused by high pressure and temp in the combustion process. The usual cause of failure is over advanced ignition timing (not adjustable in your case)and lean mixtures(also not adjustable) and inoperative EGR system(not used on an 87) .These conditions lead to detonation(audible ping or may be inaudible).and an increase in NOx .I would guess cylinder deposits might have slightly raised compression also .I would try a tank of highest octane fuel available , a good hot run to preheat the catalyst and try again.

[GSpreeman]

Thanks John. I think the PO chipped my car. Is that affecting the NOx?

Aside from high octane, what else should I do? Right now I'm putting in plugs, air filter, dist. cap, rotor.

[johnsjmc]

If it,s been "chipped" most usually advance the timing more than the fuel as the fuel is trimmed by the O2 sensor anyway. If the advanced timing is causing the engine to "ping" it will increase NOx.If you were using reg gas you might be close enough to a pass with a higher octane fuel alone .Except for replacing the chip you don,t have much else to try as you passed the 2 gases which are most affected by a usual tune up and NOx is pretty close.Try to schedule the retest for a cool moist day as well.