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Cadillac Sedan Deville Failed Smog Lean Fuel Condition

I have a 1993 Cadillac Sedan Deville with the 4.9 engine has 113,000 orginal miles it is a gross polluter because NOx was too high. The NO reading at 15mph was 2809 and at 25mph it was 3294. I had a full tune up done, changed the catalytic convertor, cleaned the egr passages and put a new egr valve, new fuel pressure regulator, new oxygen sensor, new map sensor, changed the fuel injectors and it's still has high NOx. My question is I have changed pretty much everything I know of to changed. Do you think my Cadillac Sedan Deville has a bad computer which is causing the high NOx? Is my Cadillac running lean?

Answer:

The best recommendation we have in this case is that your Cadillac Sedan Deville's fuel injector pulse widths are diagnosed. You've pretty much replaced every component responsible for fuel control and NOx reduction. To find out if still the problem is computer related check the injector pulse widths to make sure the computer isn't commanding lean. Without getting too technical on pulse width frequency, check for variations in pulse width from cylinder to cylinder and check to see pulse width changes with RPMs. Use a sensitive and accurate multi meter when performing this diagnosis. No pulse width change, possibly defective computer (assuming and this is a big ASSUMING) all other emission components are functioning properly. posted by SmogTips Support

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