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1990 Cherokee pre-test SMOG fail

Old 07-26-2014, 07:31 PM
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Unhappy 1990 Cherokee pre-test SMOG fail

The STAR station I went to last year put a new cat on it back then to get it to pass smog after I fixed the NOX problem by putting a new EGR solenoid in it.
He did a manual mode test for free and says the HC and CO are slightly higher than allowed.
I have never put a new O2 sensor in it yet or plugs.
The numbers are not outrageously high , just slightly high.
He will do another pre-test/manual mode on it after I do whatever I can do.
Is the O2 sensor the culprit ?
Is it advisable to run cat cleaner through it ?
Cat is a Magnaflow and only has 12K miles on it.
Car runs really strong. Plug color looked good last year.
I want to keep it on the road but here in CA you have to do mine every year and I don't have/want to spend a lot on it to get it to pass.
It only uses about 1/2 QT every 5K and has 257K on it.
Suggestions ???
Old 07-27-2014, 08:58 AM
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Year: 1996
Model: Cherokee
Engine: 4.0
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Originally Posted by bufbarnaby
The STAR station I went to last year put a new cat on it back then to get it to pass smog after I fixed the NOX problem by putting a new EGR solenoid in it.
He did a manual mode test for free and says the HC and CO are slightly higher than allowed.
I have never put a new O2 sensor in it yet or plugs.
The numbers are not outrageously high , just slightly high.
He will do another pre-test/manual mode on it after I do whatever I can do.
Is the O2 sensor the culprit ?
Is it advisable to run cat cleaner through it ?
Cat is a Magnaflow and only has 12K miles on it.
Car runs really strong. Plug color looked good last year.
I want to keep it on the road but here in CA you have to do mine every year and I don't have/want to spend a lot on it to get it to pass.
It only uses about 1/2 QT every 5K and has 257K on it.
Suggestions ???
2 cans of dry gas in a full tank works for me.
It isn't illegal to use dry gas in your vehicle.
Old 07-27-2014, 09:17 AM
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Year: 1997
Model: Grand Cherokee
Engine: 4.0
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The O2 sensors get weak after about 100K miles. Replace it.
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