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Don't replace, troubleshoot Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 7 Mar 2002 13:00:31
In Reply to: failed NJ inspection - 2nd time - now what.., marko, Thu, 7 Mar 2002 12:27:27 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Replacing parts is what most mechanics do. Troubleshooting is what GOOD mechanics do. Troubleshoot a lot, replace once.
An AMM is about $150 for a rebuilt, and a Cat a few bucks more. That would buy a decent amount of troubleshooting, and may save you a bundle.
In general, high NOx is due to lean running. Yes, a bad O2 sensor could cause lean running. But so could a bad AMM, Fuel Pressure regulator, wrong timing, or something as simple as a vacuum leak.
First, find out if your car is running lean. Look at the spark plugs - do they look whitish? Then you're probably running lean. First off, check for vacuum leaks in hoses. You'd feel pretty silly dropping $500 in parts if the problem was a cracked hose for $2.
Next, use a good voltmeter to measure the voltage output from the O2 sensor - but keep the sensor hooked up. If you're running lean, it would be showing a low (close to 0.2 volts) value - Rich looks like around 0.8 volts or so - not a big voltage swing here. Your AMM may just be out of adjustment - in the '86, there is an adjustment screw. Check the archives for how to adjust an AMM.
If the spark plugs look good (light grey) and the voltage on the O2 sensor swings back and forth about 1/second between 0.2 and 0.9 volts, then the engine isn't running lean. Then, and only then, would I suspect the catalytic converter. If the engine is running lean, it's producing more NOx than the converter can handle, so don't blame the cat. If the engine is running right, then think cat.
That's a start, anyway.
Good luck!
posted by 140.157....
, Thu, 7 Mar 2002 18:01:11, Thu, 7 Mar 2002 13:00:31 <-- Viewing This Message, Thu, 7 Mar 2002 23:20:24
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