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Jun 4, 2003 | 04:56 PM

explorer724

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code420

code420- i changed my oxygen sensors all 3of them.also had a tune-up-changed plugs,wires,filters,oil.coil-and just had it inspected and it passed.

Jun 5, 2003 | 08:30 AM

thelonerangerxlt

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code420

724, my book says code 420 is "Catalyst system efficiency below threshold (bank 1). That sounds to me like a catalytic converter problem on bank 1........???

Jun 5, 2003 | 08:46 AM

thelonerangerxlt

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code420

724, it seems that a degraded catalyist (code 420) can be caused by a slew of things: lean mixture, rich mixture, running leaded gas, high fuel pressure, wires crossed on O2 sensors, vacuum leak, misfires, just to name a few.......

You probably have a partially melted cat on bank 1. I would pull the codes; this will indicate what caused it.