Have you removed and checked the EGR and the intake for carbon build up? As far as the fuel pump, under a load, if there isn't enough fuel pressure, it may start running lean and the O2 sensors will tell the computer to richen the mixture. I know it sounds odd, but it happens. There are so many computers and sensors on vehicles today, one thing can set off a chain reaction of events.
Friday, February 18th, 2011 AT 2:19 AM