06 Freestar LTD - Ran fine, had plugs/wires replaced, now P0420 DTC

[jcasaccio]

Hi Just had my plugs and wires replaced as part of 60k maintenance. Went to Midas. They had a really hard time with this, kept getting misfire issues. Finally had it resolved, but the 2nd drive of the car tripped the Engine Service light. I went to the local auto parts store to have them ck the codes and it's a P0420 - Cat efficiency low on bank 1. I know the Midas folks said they had a lot of misfire issues once they changed the plugs, and kept trying to fix it -finally was a bad new plug in #3 cylinder. I researched this code and found misfire can cause damage to the cat converter. Any other ideas of what changing plugs and wires would do to cause this code? The Midas experience was kind of annoying - took much longer than planned for them to do this and they had many issues. Said they had to drop engine cradle to get to plugs - could they have damaged the exhaust system in doing so - leaky exhaust can also give this cde - from what I have read. Thoughts? Thanks JC

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[BlackSton3]

My first thought (with all due respect) is why did you bring it to Midas? My second thought, unfortunately, is that you'll have to bring it back there since they are totally responsible for your problem and subsequently responsible for making things right. Good news is that their primary expertise is exhaust, so your cat will probably get replaced correctly.

[Use Common Sense]

They could have cracked the O2 sensor, pinched a wire. There was no need for them to "Drop the engine cradle" to get the plugs out. If they had it on a lift, the rear plugs can ge gotten from underneath with very little effort. I've done my Freestar once a year on car ramps when I was running copper core plugs (water injection) in 1/2 an hour laying on the ground untill I put the iridium plugs in. And if they actually changed the wires, the easiest way is to remove the cowling. Pop the wiper arms off and just a few screws and the rear plugs and the coild pack are fully exposed. Did they put dielectrical grease on both ends of the plug wires? Are the plug wires locked in their original wire loom/locks and routed the original way to eliminate cross firing? Any plug wire that crosses another should be at as close to a 90 degree cross as possible. If not, this can also cause mis-fires. I would hold them responsible for any damage that may have occured to the converter as this animal isn't cheap unless you're still under the emissions warranty time/milage.