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Old 08-15-2020, 09:17 PM   #1
drj434343
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Default 1990 EJ22 Manual Legacy failing smog

Failing smog in Oregon, about 30% higher than max allowed in HC and CO. NOX is not measured in OR, and all tests are done at idle only.

Here's what I've done to troubleshoot so far.

- Checked air filter, it's nearly new with no buildup
- Checked spark plugs, they were all in in good shape with proper gap
- Checked and cleaned the MAF. There are no bench tests I know of for this.
- Checked the fuel pressure; within spec at 38psi with no regulator vacuum
- Resistance of coolant temp sensor within spec at operating temperature and IR thermometer checks confirm getting to temp
- All injectors within resistance spec and appear clean
- O2 sensor showing 0.8 V on voltmeter, and shows cycling on oscilloscope
- Smoke checked intake system and found no vacuum leaks

The tailpipe smells like its running rich, but I've seen no drops in mpg or power changes to suggest a rich condition. Plugs were a light grey and dry.

I'm left with the idea of a bad CAT, but the current CAT has only 20K miles on it. Also, I'm not sure if a poorly performing CAT can actually cause the exhaust to start smelling.

Looking for some advice, I'm at a loss.
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Old 08-18-2020, 01:13 PM   #2
yarrgh
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is it an aftermarket cat? they usually don't last too long, which is why they're so cheap. You can pull/clean the injectors to make sure they're not leaking.
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Old 08-18-2020, 05:14 PM   #3
drj434343
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Thanks, a new CAT is definitely moving to the top of my list considering the test results, but I'm not used to the exhaust smelling like it does just because the CAT died. That's the bit of anecdotal opinion I haven't found yet.

Someone mentioned checking the vacuum hose of the fuel pressure regulator as it can leak fuel past the diaphragm into the intake. Other then that, or swapping in another used MAF, I feel out of non-CAT solutions.
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Old 08-18-2020, 06:29 PM   #4
Elbert Bass
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Test your MAF signal with the scope. Look for a noise signature just under the signal pattern. I have seen those old MAF sensors read spec voltage but cause a rich condition due to a noise signal. The only way to verify is with an o-scope.
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Old 08-18-2020, 08:21 PM   #5
drj434343
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Is there a published procedure for that back probe? Like which pins and what signal to look for? I have an O-scope but the factory technical manuals don't provide any guidance, and I thought those would be the most complete guides.
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Old 09-19-2020, 11:23 PM   #6
blackroadster
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A 1990 needing to pass emissions is why I'm happy I don't live in California. In Texas, after 25 years, the vehicle is emissions exempt and only has to pass a safety inspection.
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Old 09-20-2020, 12:03 AM   #7
Wannabe WRX
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If your exhaust is giving a smell, with high hydro and carb-mono, you have a failing (or completely failed) Cat. If you want to pass emissions with that car, you're gonna have to bite the tank-shell sized bullet here and buy a new one.
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Old 09-20-2020, 12:43 PM   #8
Elbert Bass
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Quote:
Originally Posted by Wannabe WRX View Post
If your exhaust is giving a smell, with high hydro and carb-mono, you have a failing (or completely failed) Cat. If you want to pass emissions with that car, you're gonna have to bite the tank-shell sized bullet here and buy a new one.
If the car is truly running rich a new cat won't fix it. He'll just ruin another cat. You have to fix the cause of the rich mixture first. It's possible (however unlikely with an aftermarket cat) that the cat is OK. I have seen it go both ways - but ALWAYS had to fix the enriched condition first before passing judgement on the cat.
OPs issue is he is not OBDII capable and can't know if he's fixed without a sniff test.
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Old 09-20-2020, 01:00 PM   #9
Elbert Bass
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Quote:
Originally Posted by drj434343 View Post
Is there a published procedure for that back probe? Like which pins and what signal to look for? I have an O-scope but the factory technical manuals don't provide any guidance, and I thought those would be the most complete guides.
No, in fact my Subaru Field Engineer and the techline guys go glassy eyed when I started talking about it. That's the difference between learning enough electronics to get by in your job and studying electronic engineering for 3 years like I did before getting sidetracked in the car business in 1978.
I no longer work for Subaru so I don't have access to the manual anymore. If you have FSM look in the ECM input list and find the pin number/connector for the MAF signal wire, then find that pin on the wiring diagram and that will tell you the wire color/position you need to test. I want to say black with white trace but double check.
Failing that test all with the scope - one will be ground (no signal) one will be Battery or 5 volts, one will be a smaller voltage than battery (intake temp), one will be a sine/or square wave (air flow). That will be the one to look for the noise.
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Old 09-25-2020, 12:35 PM   #10
rubbachicken
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Two places I'd start,
Go find a used set of injectors, send them out and have them rebuilt, Mr Injector, I send him injectors to be rebuilt all the time, under $20 a piece, I've been very happy, https://www.mrinjector.us/.
Having a set rebuilt, means the car is not out of action, while they are being done.

Next go buy another cat, I know of people who just put them on for the smog, take them off again until next time, not saying you should, but I know of people who do.


Next a full tune up, new spark plugs, a visual on old ones, and don't cheap out, buy a set of quality plugs, NGK are my go to's.


That is three, oh well, my counting has never been up to much.
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