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I have a 1993 Subaru Legacy L Wagon with 181,xxx miles on it. I took it for an emissions test today and it failed on the last reading. I have already done a tune-up, new plugs, wires, oxygen sensor on the car. The oil was just changed as well. Here are the readings:

 

Oxides of Nitrogen (NOx): FAIL

State Standards 2.2000 GPM

Inspection Reading 4.01666 GPM

 

What do you think could be the cause? Here are some things to look at (according to the emissions):

Air to fuel mixture too lean

Oxygen sensor not functioning properly

Inproper EGR re-circulation

Malfunction of engines spark advance

Air intake temp too high

Cooling system not functioning properly

Corbon deposits on engine intake valves

Catalytic converter partiallly clogged or not functionsing properly

 

Here is what I have replaced in the past few months:

Temp coolant sensor

Oxygen Sensor

 

I checked all the hoses and they are fine. The PVC is good. I ran some fuel injector cleaner about a month ago.

I heard that the "Guaranteed to pass" that they sell in the auto parts store cleans out the fuel and intake system. Is that true?

 

Does anyone else have any suggestions? I have read over the previous posts about emissions. Iam guessing the car is running hot. The temp gauage is normal, but the fans always run constantly. Should I replace the thermastat? Could the cat be bad? Or, too much carbon buildup? I would think that is the cats were bad and the car was running fine, it would still pass.

 

Thanks

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Paul, too bad you're not in Seattle. However, I re-read your post. Whatever are they testing NOx for? I thought that was only a problem for diesel engines and shouldn't even be tested on a gasoline engine. Sorry, shows you how much I don't know on emissions.

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Oh, they test NOx alright.

 

NOx is a result of high combustion temps. Do you know what the limits are? Do you know how far you were out?

 

Premium gas *MAY* lower NOx numbers, it also *may* raise the others.

 

No EGR on the '93. Hmm.

 

You might try a combustion chamber cleaner. Carbon may have built up, artificially raising the compression ratio, and causing detonation.

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Here is a good cheat I have used in Colorado to pass test.

 

 

Run the gas down to about 1/4 tank, then put in 4-5 bottles of Heat, this is a winter gas line dryer. I have passed several cars that failed at 1st, then did nothing but this and they all have passed.

 

 

These were in Colorado, so not sure if altitude may change, or if this will work for you but cheap easy try for a fix.

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Thanks for the suggestions. The NOx state level is about 2.xxxx and my car was 4.xxxxx. It was double the emount. I have a feeling the engine is running hot or pre dentionating. If so, how could that be resolved?

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Try a thermostat change/coolant flush if you are overheating. Make sure your radiator isn't loaded with deposits. Detonation may be solved simply by running a higher octane fuel.

 

Alcohol in the fuel aka HEET will lower all numbers dramatically, if enough is used. Do what rweddy suggests.

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Iam going to use the HEET product. There are many to choose from. Would this be the one to use: Sure HEET Fuel Oil Conditioner? Or just the plain HEET? I want the one that has the most alchohol.

 

Please check out the link:http://www.letsmow.com/gold.html

 

Thanks,

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You guys aren't really giving any solution to the problem....you're trying to fix the symptom.

 

i hope I don't come across as an rump roast....not in the best of moods right now.

 

NOx is high heat, and is typically caused when the mixture goes lean.

 

The 90-94 legacies do not have an EGR valve. These motors also tend to run pig rich.....so to fail on a NOx test is a huge indicator something is not right with the engine or catalytic converter.

Where did you fail the NOx test.....at idle or higher rpm? They didn't load test your car because it's AWD correct?

 

I would check for a vacuum leak of some sorts, and I would also be curious to know the condition of the cat converter.

 

If you pull the plugs out....what do they look like? If they look good and everything's normal......I'd really start wondering about the cat converter.

 

Subaru uses a two stage cat converter. The first converter handles reduction stages of the chemical reaction and then the second handles the oxidation stage. I'm pretty sure that's the right way.

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I had my 91 Legacy tested for emissions around mid December last year, and failed because of a high NOx reading. Knowing beforehand that the rear cat had been removed, I wasn't surprised. The reading wasn't even close, it was more than double the allowable ppm. They did a motorvac and retested it, and it passed. The RPM on the test was different so I suspect that they "play" with it a bit to get you by. If it had failed the retest I still would have received a conditional pass because the cost of a replacement cat would have put the bill over the repair cost limit. The conditional pass is good for 2 years (like a normal pass) but you must pass the next test, you can't pass conditionally again, so it gives you 2 years to fix it or get rid of it.

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It looks like the front CAT is original, but the rear cat has been replaced. I do not know when, since Iam the second owner. Should I replace both CATS? I noticed the first CAT has the Oxygen sensor (which I replaced two moths ago). I checked the computer and there are not any codes, the CEL just blinks 4 times, two second pause, then four more times and keeps repeating.

 

I took off the Air Control Valve and cleaned the carbon off of it. I just replaced the plugs about a month ago. The old plugs looked fine, but the car was running terriable at that time. It was missing and hesitating very bad. What could make the plugs fail? After replacing the plugs, it runs perfect. This makes me think that the CAT's are clogged or needs to be replaced and are causing the car to run HOT? They do not smell nor sound like "rocks" inside. What do you think about the cAY cleaners they have on the market?

 

I do not know if this is normal, but there is alot of pressure that is released when I unscrew the gas cap. Is this normal? Could the purge seloniod valve be faulty and will that cause pressure in the gas tank?

 

I just replaced the thermostat the other day. I have noticed that on occasion driving at 55+ in cold weather, the temp would rise past the mid point. Then, if I would downshift or accelerate, the temp world drop past the midpoint. I thought the thermostat could have been stuck partically closed?

 

We have the "treadmill" test here. I have a feeling it failed at higher RPM's because two years ago they just did a tailpipe test and the car passed (the tradmill was not working at the time).

 

It looks like the Emissions pricing has gone up here in Maryland for failed autos. If you fail, you must show $450.00 work of receipts done to the vehicle relating to emissions. They started at $250 and keep going up and up!!

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Because subaru uses a two part cat......if they replaced the cat improperly that could be the cause.

 

Does the CEL blink all the time even when the diagnostic connectors aren't plugged in? You may want to check out my site for more info on how to pull any codes.

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Your site is great, I had printed out the codes. The CEL does not blink when the wires are not connected. It only blinks when the wires are connected and the iginition is switched to ON. There are no codes stored in the computer at all.

 

The last options for me is to replace the CATs I would think. iam going to run some of the CAT cleaner through the system and then run some of the carbon buildup cleaner through. Hopefully, this will cut down on the high level.

 

What do you think would cause alot of gas pressure in the tank? purge valve bad?

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So with just the black connectors connected, you get a steady blinking CEL indicating no codes?

 

There is bound to be vacuum/pressure in the tank......I get that hiss when I get gas.....it's not a big deal.

 

I guess try the cat stuff......

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