Well, I've had to put my daily driver into the shop and have been driving my truck this week. Monday I noticed the MDS not engaging on the way home and watched my mileage drop significantly. I figured it may have to do with the oil being ready for a change, so I changed the oil Tuesday morning and drove to work. Seemed ok on the way down, but on the way home still the same issue, MDS was working the first 20 miles or so of the trip, but then I was in 8 cylinders the rest of the way home. I haven't had time to take the truck into the shop, but the problem is intermittent. Sometimes all is ok and I switch in and out of 4 cylinders normally, and then sometimes it's always in the gas sucking V8. I understand that the truck must be at a certain temp, and at a certain load to drop to V4, but I'm driving it steady for 70 miles, on some pretty flat terrain, cruise set at 62 normally. Any ideas?? I just don't have the time right now to get it into the dealership...

 

Have you tried taking it off cruise and see if it still runs on all 8? I've never had good luck with the MDS and cruise..

 

Cruise should not effect the MDS, I know it doesn't on mine.

 

I know that SC is flat, but is there a difference in elevation between home and work? Going up even a slight incline requires more engine effort and could cause you to run on 8 cylinders. I do not have MDS (2004) but I can see the fuel usage change on the overhead. I make frequent tips to Baltimore from Northwest Jersey. The difference being about 900 feet as Baltimore is at sea level. That equals an average net change of 4 1/2 feet per mile. 200 miles each way, I average 16 mpg going down and about 14.5 back up. The difference is larger in the car

 

Dealership re-flashed my PCM, all is well now, for anyone else that runs into this problem...