Question about 2003 Ford Expedition

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How do you know whens the cadilac converter is Bad/

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When it is 14 years old - you replace it

When it fails - you replace it -- AFTER you make sure you have no cylinder misfires,vacuum leaks & all data & sensors are okey

You have to look at scan tool data for the oxygen sensors

If the Emission Monitors do not run--that is a key

If you have O2 Sensor Codes-you check switching times with
an oscilloscope,especially if the front to rear switch bias voltage
is not with range. (that is what sets the PO420 & 430 OBD Codes)

On your vehicle-- I can tell you it is unlikely the spark plugs have been changed & not every 3 years
Also the ignition coils fail on Fords after 6 to 7 years-then you get
cylinder misfires that ruin the converter
Some 5.4 motors had leaking injectors-they take out a converter in a couple months

My suggestion:

New Spark Plugs
8 New COP Ignition Coils
New Front Oxygen Sensors-at 100,000 miles
New Exhaust Converters
Mail away your 12 year old injectors to be tested &
Ultra-Sonically Cleaned
Clean MAF Sensor

Not knowing about vehicles & the required Preventative
Maintenance, is why you have those problems

Posted on Nov 18, 2014

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  • 31 Answers

Loss of power and some times overheating

Posted on Nov 18, 2014


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The codes your car are throwing up and important codes to get fixed. The O2 sensor code is there because the cadilac converter was removed. The O2 sensor measure the amount of oxygen present in the exhaust both before the cadilac converter and after. When the measurments are the same the computer knows the cadilac converter is not working properly and it turns on the Check Engine Light. This code in itself will not effect the performance of the vehicle in any way OTHER then emissions. This is bad for the environment and if you live in a place that requires emission testing you will fail and eventually your resignation will be revoked making it illegal to drive that vehicle. It is illegal for a shop to remove the cadilac converter without replacing it so I recommend you avoid that shop in the future. There is a $10,000 fine if they are caught **** this.

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