Whats the relationship between Ford 4.0L “Check Engine” lights and new valve springs?
Some 1997-2002 Ford vehicles equipped with the 4.0L SOHC VIN E & K engines may display a check engine light “ON” with diagnostic trouble codes (DTC) P0300 (Random Misfire) or P0301. The DTC will set when the engine is operated at high rpms (4,800 rpm and higher). The misfire code results due to system interaction of higher than expected transient exhaust system backpressure (under heavy acceleration) coupled with valve spring resonance points experienced at these engine speeds. This interaction may cause the exhaust valve to hang open at engine speeds of 4,800 rpm and higher. Revised valve springs should eliminate the stored P0300 and P0301 codes on some vehicles. After verifying that the DTC sets only at 4,800 rpm or higher, remove the old intake and exhaust valve springs (p/n F77Z-6513-M) and replace them with new service intake and exhaust valve springs (p/n 2L2Z-6513-AA). Note: All twelve valve springs (six intake and six exhaust) must be replaced in order to maintain and ensure th
