Loss of MPG Kenworth 2009 C-15

Any help with diagnosis...

Kenworth 2009 C-15 with 3:36 rears and an Eaton automatic...

Over the last three months my MPG is down 1-2 mpg. I replaced an ARD head and the temp sensor in the ARD head 3 weeks ago when I also changed the primary air filter and changed the oil in the transmission. This weekend I had the fuel PSI checked and it was idling at 110 on a mechanical gauge. There are no codes on the ecm and there is no check engine light.

The truck has recently begun surging in the mornings and has been surging but only going downhill on cruise control. It reminds me of a sound like someone is dripping fuel into the system. It will rev up a little then subside, rev up a little then subside, but if I give it a little accelerator it stops and then as the day goes it goes away.

The engine fan is also running 80-90% of the time on both heavy and light loads with the a/c on and off.

I wondered if it may be the air charge cooler and my next test will be to see if I have a leak there. The engine has 2 thermostats if one went out would it cause these issues.

 

It stays steady under 200 but something I forgot is the engine fan is running 90% of the time now...

 

Ended up with a split diagnosis. I had a check engine light come on and the engine wouldn't regen and began derating. Went to Atlas Tire and Truck Center in Channelview and the mechanic looked at in and ran the wires and found that the plug was only clipped in on one side on the dpf regulator control. He pushed it in the light went out and it regened.

I drug a 40000 lb load to St Joseph Mo as I started out the A/C was off (Im assuming the mechanic fiddled with wires) and the truck ran normal with the fan working properly. My hot natured self I turned the a/c on and immediately the fan went back to running 95% of the time. I watched some videos and looked for a picture of the high pressure sensor and couldn't find it.

Finally I watched a video of a guy in a prostar truck who pointed out all the compenents on his A/C and explained their function. I went out to my truck and found the sensor in the engine side of the radiator which I push/pulled and disconnected reconnected it. I also ran the wires and gently push/pulled and fondled the rest of the similar looking connectors. Then I closed the hood and went to sleep.

Started off this morning and up to now at lunch time the truck is running its beautiful normal self with no engine fan constantly running.