I was getting a 55 code. Truck would run smoothly at first and then start idling really rough. I tried several ECM boxes gotten from a pull apart yard, with my old chip in and the truck had the same symptoms. I was advised to replace the chip in the ECM. Installed a 'high performance' chip (aftermarket as oem no longer available).

Now I still get the 55 code, even after resetting computer with my reader and leaving the battery disconnected overnight. The difference is that NOW the truck idles very rough for several minutes and then smooths out. When I turn the truck off and try to restart, it is necessary to push the accelerator all the way down to get it to start. Sparks are getting coated with carbon, exhaust backfires a bit and smells like fuel.

I really need this truck to run. Any advice is appreciated. Thanks in advance.

 

I'm leaning towards a connector. Is the plug into the ecm clean? Might try some contact cleaner.