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Discussion Starter · #1 ·
I'm having a hard time trying to pass our aircare test with my SHO.

Originally after I bought the car, I took it through the test, and failed on Hydrocarbons only.

The readings are:
HC g/km= 0.7553 MAX 0.5000 FAIL
CO g/km= 2.1388 MAX 9.3200 PASS
NOx g/km= 1.0371 MAX 1.2400 PASS

So I proceeded to do a full tuneup, seafoam (worst seafoam i've ever done) plugs, wires, air filter, fuel filter, Pennzoil Ultra oil change, no PCV valve on this car (factory).
Someone also told me to put a litre of methyl hydrate in the tank to mask the HC's. I think it boosted my NOx's instead.

I then tried again, and it got worse.

HC g/km= 0.8558 MAX 0.5000 FAIL
CO g/km= 3.2470 MAX 9.3200 PASS
NOx g/km= 1.2483 MAX 1.2400 FAIL

Now I just realized that the previous owner was using 87 octane 10% ethanol, and that's the gas that I have been testing with. I've now got a full tank of 92 octane ethanol free. Could using the wrong gas cause different readings on a car designed for premium fuel?

The only other thing I haven't tried yet is changing the O2 sensors. With the age on them, they probably could be done and bump my readings down a bit.

If I do that, should I reset the computer again? (I did it after the tune up so that it can relearn the mixtures, then I took it for a 60km drive.) Does the EEC-IV have a drivecycle to get the leanest mixture? That could be also why I didn't pass, maybe I didn't drive it long enough.

Other thing I could think of is the Catalytic converters. There's 3 of them on this car. Not looking forward to the cost of replacing those.
 

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Haven't worked on a SHO before, does this engine have a egr valve? If so, take it off, clean out the passages and tube. I would change the o2 sensors if it's never been done on this car. Is the car going through, or burning any oil? That would also up the hc readings. After replacing sensors, you want to disconnect the battery for 10 min or so, so the pcm can re-learn conditions with the new sensor. What state do you live in? I know Texas offers up to $600 to repair a car that failed smog, provided you owned the car for at least 1 year.
 

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Dumping a couple of cans of dry gas into the tank before testing will help, the car needs to be at least operating temp, hotter is better.
 

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Discussion Starter · #5 ·
Yes, car was up to operating temp. I had driven the car 2 hrs prior to each test.

I finally got a code last night. Code 172. RearO2 sensor not switching/indicating lean. That would do it, PCM would go into enrichment mode.

So I've got the O2's (going to do both at once) and if for some reason it doesn't pass, I've heard I can pull the SPOUT connector, which retards timing to 10BTDC. A lot of people said they passed with that, and some people have passed with no Catalytic Converters with the SPOUT removed.
 

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Spout will help with the NOx emissions.

How many miles are on the cats?
 

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Discussion Starter · #7 ·
Spout will help with the NOx emissions.

How many miles are on the cats?
I'm not sure. They don't look original, becuase the welds don't look original and it says obd-ii compatible on them, and this car is eec-iv. So not the original cats.
 

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I finally got a code last night. Code 172. RearO2 sensor not switching/indicating lean. That would do it, PCM would go into enrichment mode.
My SWAG is that you have a vacuum leak which is causing one bank to run lean. That could cause poor combustion, upping the HCs and the NOxs, and therefore the rear O2 sensor stopped switching.

Are there any exhaust leaks upstream of the rear O2 sensor?
 

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FWIW I would guess E10 87 octane would be best for the test anyway.
 

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Yes, car was up to operating temp. I had driven the car 2 hrs prior to each test.

I finally got a code last night. Code 172. RearO2 sensor not switching/indicating lean. That would do it, PCM would go into enrichment mode.

So I've got the O2's (going to do both at once) and if for some reason it doesn't pass, I've heard I can pull the SPOUT connector, which retards timing to 10BTDC. A lot of people said they passed with that, and some people have passed with no Catalytic Converters with the SPOUT removed.
Can't get away with that here, they check the engine compartment and all the emissions components (as well as look under the car with a mirror), to catch people trying to "make" it pass. You should pass with new o2 sensors, and no vac leaks. Just wait until it goes though several warm-up cycles before getting re-tested, so the pcm relearns everything. Don't put anything other than gas in the tank before the test, cleaners and additives can make the readings higher. Mine just passed last week, and how ironic, the next day I had the P0300 code from moisture in the gas.
 

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Discussion Starter · #13 ·
After changing the O2's and driving for a day:

So latest test results:

HC g/km = 0.8971 MAX 0.500 FAIL
CO g/km = 3.4085 MAX 9.3200 PASS
NOx g/km = 1.6923 MAX 1.2400 FAIL

At this point I decided to remove the SPOUT jumper, as instructed here. Results got better but not perfect to pass.

HC g/km = 0.6266 MAX 0.5000 FAIL
CO g/km = 3.3641 MAX 9.3200 PASS
NOx g/km = 0.9225 MAX 1.2400 PASS

But not enough. A shop I know is going to test the cat converters, but i'm sure now that is the issue here. New cats should bring my HC down enough to pass emissions.

Also, aftermarket cats usually only last a few years, and they look like they have been changed already.
 

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Hydocarbons tend to mean misfire or incomplete combustion, I'd suggest having a look at all 6 spark plugs...
 

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Discussion Starter · #15 ·
Hydocarbons tend to mean misfire or incomplete combustion, I'd suggest having a look at all 6 spark plugs...
I have installed all 6 spark plugs brand new last week. Also, the old ones didn't look bad at all.

I'm going to put new converters in. I just found out today that they are cheap aftermarket HI-FLOW cats, and I know aftermarket cats don't last as long as stock ones due to the precious metal content being a lot lower.

I'm just going to put in good ol regular direct fit cars. Last time the cats were changed (the cheapo high flows) the readings were:
HC's - CO's - NOx's
0.12 gm/km0.34 gm/km0.01 gm/km
and that was 5 years ago.

Time for new ones.
 
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