On the 2000 Ford F-150 with the 5.4L engine, the NOx being high is usually most associated with a problem in the EGR System. The NOx means there is too much exhaust gas not being recycled properly and this very well could produce a knock or ping. So, best place to start here is by checking all the vacuum lines to/from the EGR Valve, EGR Pressure Feedback Sensor and EGR Control Solenoid making sure there are no cracks, holes or loose connections (inspect these carefully! This is common, especially at the DPFE!). Next, would be to clean the EGR Passages. Remove the EGR valve and using some throttle cleaners and a flat-blade tool, scrape out as much build-up as you can while trying not to let too much fall inside. Inspect the EGR for signs of any build-up as well. Sometimes it can be cleaned, but more times than not, if build-up is found, it will need to be replaced. If all of these check ok, or cleaning/replacing doesn’t solve the problem, the DPFE Sensors are extremely common well-know fail items and replacement would be the next step. The gasket WILL need to be replaced and the mounting surfaces perfectly clean and smooth to reinstall. Make sure to clean the passages and the EGR Tube as thoroughly as you can. Again, triple-check those vacuum lines, especially the DPFE and Vacuum Solenoid. IF the cleaning doesn’t help, look into the DPFE and/or the Solenoid functionality.
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