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Old 07-25-2014, 03:09 PM   #1
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Default Need help with a code

2004 Ford F-150 5.4 V8- 114K miles, tune up at 97K.

I noticed my truck was running kind of rough and had a hesitation when I'd give it gas from a stop. I went and had the code read and it was P0420, Catalyst System Efficiency Below Threshold (Bank 1). I've been trying to read up and see what could cause these problems and there's a laundry list but none of the problems match up with my symptoms.

When I take off from a stop, my truck feels like it's bogging down, like I'm pulling 50K lbs behind me. However, if I "gas it" then it will clear up. It seems to only do it around 1500-2000 rpms. I'm leaning more towards the passenger side cat being toast, but any and all help would be appreciated.
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Old 07-30-2014, 10:20 AM   #2
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Default A guess, if I may

Hello, I've only replaced a few of these sensors; an upstream sensor in a 1997 F-150 4.6L being the most recent.

Since your code is relevant to a downstream sensor MAYBE it's economical to replace that sensor (downstream, right) first. Kira
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Old 07-30-2014, 10:28 AM   #3
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It's most likely the O2 sensor or the Cat...but I think your 04 has 4 cats..
08 FX4... Flowmaster Exhaust, line-X, Sky Jacker leveling kit. 295/65/20 Nitto trails mounted on 20 X 9 Carroll Shelby wheels. AIRAID CAI. Harley headlamps and LED Tails & 3rd brake lights,custom upper and lower Grill. Edge Evolution. Interior/Exterior LED lighting, NFAB step bars, America Tri-fold Tonneau cover.
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Old 08-01-2014, 12:03 PM   #4
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Alright, don't hate on me, I'm a 3rd gen mechanic and I always tell my customers to try this first before they go dropping big bucks on chasing down the 420.

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Old 08-01-2014, 02:58 PM   #5
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Thanks, I'm always hesitant about adding things to my fuel, no matter what it is, I've also thought about taking it apart and cleaning it too.
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Old 08-02-2014, 01:42 AM   #6
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Check see any exhaust leak or any crack around cat convert area.
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