2012 Expy Cat flow problem

[Kiteman]

Have a 2012 Expedition Limited, 5.4 Triton. After replacing the engine with new, I started getting P0420 & 0430 codes. Dealer determined it was not a Oxy sensor problem - all 4 checked fine - but that the Cats were bad. Exhaust shop confirmed. Had Cats replaced with Magnaflow Performance Cats. Still getting codes. Ford dealer and exhaust shop found the Cats were overheating - turning purple! He replaced under warranty, but new ones are still throwing the codes. Ford tech found they are creating too much back pressure. Anyone had this problem and have suggestions? Mileage seems a bit off, but runs/tows fine! Mostly tired of seeing the light & worrying it might be another code! THanks!

 

[Trainmaster]

Is anyone taking responsibility for this cluster of misdiagnosis?

Something's not working right, and to determine what it is, you'll have to know how the diagnoses were arrived at. We doubt three sets of converters - including two new sets from the factory - are bad.

Perhaps you should find out how the oxygen sensors were tested.

New stainless turns colors with normal use. I hope the casing's "turning purple" isn't the "tech's" means for selling you a fourth set of converters.

I would get these oxygen sensors' voltage measured with a meter. I'd check the converters' temperatures with an infrared thermometer. And I'd check the exhaust contents with an exhaust gas analyzer.

To do anything less would be throwing more parts at the problem, and we see how that's working out.

 

[Kiteman]

I'm going back & forth between out ford dealer and the exhaust shop.

The Ford techs checked the sensors and the system, results being the cats are restricting the flow enough to cause excess heat and the codes. They tested all 4 sensors - all are well within spec.

The exhaust shop replaced the set he installed with new ones on warranty - so no cost to me. When he installed the first set, it included a new Magnaflow muffler and all the pipe from the cats to the tip - so entire new system. He has contacted Magnaflow to get help with this problem, but not getting a reply to e-mail - his next step is playing phone tag with them! Hope to know more tomorrow after I stop for a visit!

Neither the shop or anyone at Ford has seen this problem before. The cats are the correct size and style for my SUV. I'll ask my rep at Ford about testing exhaust contents... Engine is new from Ford.

 

[Kiteman]

Reply from Magnaflow - the CATS are correct, they are their performance style CATS - so not restrictive. When I visit Ford, I'll ask about checking the exhaust contents - but wouldn't it running a bit rich cause a code?