ISX EGR grrrrrrr

Need some guidance on what's killing my power and mpg.

07 IH 9400 with an 06 435 isx. Got the truck showing two egr codes. Replaced the exhaust pressure sensor + pigtail and the egr valve. Cleaned the little tubes and inspected the mix pipe. Light dry soot present but no buildup at all anywhere.

Pre-repair mpg would run 7+ easily, the only sub 7s was pulling +40k across I-68. Post-repair mpg dropped to low 6 and gotten worse with time to an abissmal 5.3 on my last tank. That run was pulling a whopping 3k from northern Ohio to Wisconsin and 25k back with a pair of 100 mile deadheads thrown in. Not exactly strenuous work. Power is sluggish and the turbo has a random cough.

Now for this tank. I unplugged the egr valve and immediately laid down an 8.4 deadheading from central Ohio to Nashville then backed it up with a 7.4 back to Florence KY with 32 on the floor. Turbo cough is gone and power is back.

I don't mind driving with the egr unplugged since this truck doesn't trigger the ce light for that code but I'd like to have it working right.

 

Exhaust pressure sensor and egr valve codes. That's why those two parts got changed.......

I guess I wasn't clear enough. The codes were there when the truck was purchased. The egr valve and exhaust pressure sensor were verified defective and were replaced. At that point there were no codes but there was also no power and truck started using fuel like I owned an oil well. Now the truck has an egr valve code, sorta expected with the egr valve unplugged.

 

I was trying to be nice but... I generally don't replace $800 parts plus labor on a whim. I'm not an idiot or a rookie. If I replaced the egr valve it's because the valve was bad. Now it's not. What I want to know it what condition or failing component will cause the ECM to operate the egr valve in a way that will cost me 2 mpg and kill my power WITHOUT causing a code. Is that clear enough?

 

Ok let's start over.... I have an isx that gets crap fuel mileage, has low power, and the turbo coughs. It has no codes at all. When I unplug the egr valve my mileage improves by over 2 mpg, my power is back, and the turbo cough disappears.

The entire egr system has been cleaned and inspected, the egr cooler is not leaking, and I repeat there are no codes. There is no "mechanical" problem with the egr system. Every plug has been cleaned and inspected to the point of doing continuity checks using a fluke digital multimeter to each sensor.

Based on my 14 years of military technical experience with digital and analog electronics, and over 10 years custom tuning of oem and aftermarket engine management systems, I'm going way out on a short limb and say this is a sensor issue. I'm making an educated guess that at least one sensor in the system can get out of range without the ECM coding. I could Easter egg like 99% of mechanics but I don't Easter egg unless there's no other option.

Now about my attitude. It's based I the fact that I didn't ask for help troubleshooting any codes. I do have them btw. However I don't keep maint records inside my truck. I find its a good way to lose things and its sort of pointless. Had I needed help deciffering codes I would have posted them. Btw, I can do that several ways. See, I'm moderately skilled at reading the fault display on my dash and pretty good at reading my scan gauge d. I'm also pretty good at getting our mechanic to break out his snap on diagnostics unit when I want to see more detail.

Now, if you don't know of any sensor that could cause this issue I'd like to chat with someone with more expertise