Q: engine ping on 2001 Jeep Wrangler

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have 2001 wrangler with a 4.0. had rebuilt motor put in 1000 miles on it . it has a motor ping. its not ruming hot . has a code 420 in it, scanner shows it runing lean at times. not blowing 02 codes but was thinking bad front 02s or maybe a cooler t stat. also has new water pump and rad.
(1) Answer
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Engine pinging is caused by hot combustion chamber temperatures caused by localized hot spots, not high enough fuel octane rating, excessive cooling system temperatures and or lack of a properly working EGR system.
P0420 is a low catalytic converter efficiency code. The cat convt could be caused by a lean mixture (which may also cause pinging).
It may be more cost effective to get a repair shop with a god quality scantool to read live sensor data to so how much air is thought to be entering the engine, actual engine running temperature, fuel trim figures, and live )2 sensor data. Looking at this information live n a scan tool is quicker and is very accurate and less intrusive testing than trying to test each sensor yourself.