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1992 LS400 Smog failed. Please help.

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Old 04-17-12, 10:56 AM
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zafar11
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Default 1992 LS400 Smog failed. Please help.

HC at 1500 measure 141, Max allowed 71 (Failed), at 2500 measure 28 Max allowed 54 (Passed)

CO at 1500 Measure 1.50, Max allowed .68 (Failed), at 2500 Measure 0.00 Max allowed .38 (Passed)

NO at 1500 Measure 0 , Max allowed 524 (Passed), At 2500 Measure 825 Max allowed 687 (Failed)


So basically failed HC and CO at 1500 but passed on 2500 AND passed NO at 1500 but failed on 2500.

Please help
Old 04-17-12, 11:16 AM
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RA40
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Welcome to the forums.

This is typically an EGR valve issue. Get the tube cleaned, insure valve is working and you'll be
Old 04-17-12, 11:39 AM
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Originally Posted by RA40
Welcome to the forums.

This is typically an EGR valve issue. Get the tube cleaned, insure valve is working and you'll be

RA40, I will clean the EGR but you are sure this is not related to Cats ? I can even do the tune up. Just wanted to make sure this is not cats related. I can't afford Cat's.

Thanks for your help.

Last edited by zafar11; 04-17-12 at 11:57 AM.
Old 04-17-12, 12:01 PM
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cats are a last resort. they don't really die unless something in the fuel system is dead and spewing raw gas into them.
Old 04-17-12, 12:10 PM
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Originally Posted by PureDrifter
cats are a last resort. they don't really die unless something in the fuel system is dead and spewing raw gas into them.
Thanks Pure. That is what I wanted to hear. I hope cats are good.

I will give it a shot, I will go ahead and clean the EGR and while I'm at it I can do the tune up as well.

Will keep you guys posted.

Thanks
Old 04-17-12, 02:46 PM
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Other items to consider:
PCV and if it is throwing any codes for the O2 sensors.

After your tune-up and EGR cleaning, run premium gas like Chevron, Shell etc.
Old 04-17-12, 04:24 PM
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Make sure you warm up your car prior to the smog. Don't add any additives to the gas tank either. Do you have the oxygen readings? I would like to see it. I suspect your cat was cold when they tested it, that's why it passed 50/15 instead of 25/25.
Old 04-18-12, 11:15 AM
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Originally Posted by RA40
Other items to consider:
PCV and if it is throwing any codes for the O2 sensors.

After your tune-up and EGR cleaning, run premium gas like Chevron, Shell etc.

I will change the PCV for sure, but the bulb for check engine light is out so I first I need to replace the bulb and then look for the codes.
Old 04-18-12, 11:17 AM
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Originally Posted by GS4_Fiend
Make sure you warm up your car prior to the smog. Don't add any additives to the gas tank either. Do you have the oxygen readings? I would like to see it. I suspect your cat was cold when they tested it, that's why it passed 50/15 instead of 25/25.
% of CO2 is at 1500 it is 15.2 and at 2500 It is 15.8 .

% of O2 at 1500 is 0.0 and at 2500 it is at 1.2

Any suggestion ?
Old 04-18-12, 12:43 PM
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Originally Posted by zafar11
% of CO2 is at 1500 it is 15.2 and at 2500 It is 15.8 .

% of O2 at 1500 is 0.0 and at 2500 it is at 1.2

Any suggestion ?
At 15 mph you are getting 0% oxygen compared to 25 mph your getting 1.2% oxygen? Or is it vice versa? If it really is vice versa, your cat was cold.
Old 04-18-12, 06:07 PM
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Originally Posted by GS4_Fiend
At 15 mph you are getting 0% oxygen compared to 25 mph your getting 1.2% oxygen? Or is it vice versa? If it really is vice versa, your cat was cold.
I double check the reading I wrote above is correct.

So the cats are good then ?. I let the car idle for 30 minutes before took it for the test.

Any suggestion ?
Old 04-18-12, 08:15 PM
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idle=bad, cats don't get hot. go and drive the hell out of it (safely) or hell even revving it/holding it at a constant 3500-4500 rpm for a few minutes will help. the idea is to heat the cats so they are at their maximum efficiency.
Old 04-18-12, 08:42 PM
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Originally Posted by zafar11
I double check the reading I wrote above is correct.

So the cats are good then ?. I let the car idle for 30 minutes before took it for the test.

Any suggestion ?
At 50/15 your car is running rich. At 25/25 your car is running lean. Your car is definitely not in fuel control. When was the last time you changed your oxygen sensors? Do make sure your EGR system is working properly - EGR VSV, EGR modulator, and the EGR itself. Apply vacuum to the EGR see if engine stumbles, if not, you got a stuck EGR or clogged passages.

If your MIL is not working, I'm surprised the guy didn't fail you for it. Check to see if you got any codes, it will help the diagnosising process.
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