Just purchased a 2008 durango with a 4.7 flexfuel engine from a government agency, when I picked it up it had 1/4 tank, I assume that they used E85 regularly, I, however filled the remaining 3/4 tank with regular 87 octane E10. 170 miles after filling up codes P0420 and P0430 appear at the same time. Could the difference in the fuel cause this ?

 

Probably not. PCM should be able to account for the different fuels, that is how it was designed at least. Clear the codes, see how long it takes them to come back. Also see what kind of fuel mileage you are getting on 'real' gas.

 

Thank you for your advice, here's what happened next, cleared the codes, after 18 miles the CEL came back on, this time with only 1 code P0420, drove the vehicle until almost empty and put in 1/2 tank of E85 (which there is only 1 station within 12 miles that carries E85) and turned off the code, now after almost 100 miles there are no codes or CEL, I don't know if the change back to E85 was the solution or I just got lucky and due to the fact that it went from 2 codes to 1 code tells me that as you said the computer was compensating and probably would have adjusted to 87 E10 eventually, but hopefully changing back to E85 solved the issue, if the codes reappear I will ask again. Thank you again for taking the time to respond to my question... Sam

 

Think I would make the switch to E10, and then see what happens. Having to drive 12 miles to get gas sucks. (and in my truck, real chance of running it to low to make it that far. )