Author Topic: Cummins Poor Fuel Economy  (Read 192 times)

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Offline Blemon56

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Cummins Poor Fuel Economy
« on: July 03, 2020, 11:51:34 AM »
Hi. New to the forum... but not RVing... been full time for 10 years.  Have a 2008 Fleetwood Excursion with 92K miles, Cummins ISC 360, Allison 3000 Transmission.  I’m not a diesel mechanic but am a retired aircraft mechanic so I understand how things work. All annual maintenance has been performed by either Freightliner or Cummins... mostly at Gaffney. After initially realizing that the faster I drove, the more fuel I used, I’ve settled at 60 to 65 and would get around 7.5 mpg.  Three years ago I noticed 6.5 to 7 on the computer.  Two years ago I noticed 6 to 6.5.  Started doing my own calculations fuel stop to fuel stop over a few thousand miles and verified mpg.  Last year went to Cummins Ocala with this issue. They checked and serviced the engine and found a cracked exhaust manifold.  Went there this past February and had it replaced $$$.  I reset the trip odometer after warming up the engine and drove 72 miles at 4.9 mpg. I planned to schedule another Cummins appointment but COVID hit and am still sitting in Florida 🥵. I was hoping to put a few hundred miles on the coach to verify mpg post exhaust manifold repair. Years ago I met Ask Dave at a rally so I called him. He suggested a faulty hp fuel pump or a blocked port on a valve ( can’t find my notes). 

Planning soon to head north.  Any ideas would be appreciated.  Keep in mind that I’m not complaining about fuel usage or the cost of operating a motor home... I know the deal and am enjoying the full time RV life.  Just that the gradual change in fuel consumption over the last few years has me concerned.

Thanks in advance for your replies.