CM871 FUEL CONSUMPTION

[Optimanzltd]

Hi Guy's
Awesome bunch of folk on here, good blog to have a membership going! Hotsauce or not...

I have a problem with a CM871 ISX engine. Initially it cooked 3 x ECM when Cummins had a go at it and it turned out that on DPF regen the ECM was getting a back feed power surge frying them all up.

I sent my guy an exchange ecm with egr and dpf deleted ( I am in New Zealand so this is not a problem) and it has all the @m*m^2 goodies, including a 660 Hp tune. Worked fantastic, and no more ECM issues.
Initially it went fine and was great on fuel and power. This was beginning of January 2016.

In the last month it has gradually lost more and more power and started using more and more fuel.
It was using about 5 MPG (2 Km per liter) which is quite good for here, now it is down to 2.9 mpg (1.2 km per liter). No turbo or intake or inter cooler issues, this was checked by a local Cummins dealer who seemed knowledgeable on the phone.

Any idea's before I send the guy another ECM to make sure it is not an ECM problem?
I am thinking fuel pressure / fuel flow?
Thanks in advance.
Jack