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[BeatMarti]

I recently bought a great scanner tool (highly recommendable from Autoenginuity with Ford extensions using a PC for about $350) and started to do some analysis using the shop manual as a guide:

I recorded samples of various PIDs while driving a long uphill at full load. It was very apparent to see how the de-fueling kicks in when EGRT(a) reaches 1400 degrees. Problem with this is that the temporary de-fueling significantly reduces power (about 150 foot pound and 700 RPM drop) resulting in the EGRT to drop to between 1200 and 1300 degrees for a little while, then it'll increase the power again until the temp reaches 1400 or thereabouts. The cycle begins again.

I noticed right away that the IAT sensor (combined with the Mass Air Flow sensor) was biased to show a +35 degrees error and the IAT2 sensor (the one on the manifold) shows a -30 degrees error. Both errors are greater than allowed tolerance by Ford. I started with replacing the MAF/IAT sensor. Now, the IAT shows the correct temperature and the engine ran significantly better when pushing up a long 10% grade! It was morning (ambient temps around 60 degrees) - no problem at all. It felt just like when it was new! (Also, it had just finished a regen cycle).

Today (ambient temps around 80 degrees) I came back over that pass and found it had a lot of trouble staying under 1400 degrees EGRT(a) temp and consequently, I had less power, but still a bit better than prior to changing the MAF/IAT sensor. I am planning to replace the IAT2 sensor as well since it is off by quite a bit hoping that it will further reduce the problem. One other observation: This was after about 80 miles since the last regen cycle.
It is quite apparent that the EGRT(a) temperature reaches 1400 degrees much faster once the DPF is starting to clog up.

One other thought I had: What if (due to use of a programmer) the EGRT(a) temperature reached a really high point (let's say 1500 degrees) and damaged the sensor. When you look at the shop manual, that sensor reduces resistance with temperature increase. It is conceivable that the sensor is actually reading maybe as much as 100 degrees more than it should when within 1200 - 1500 degree range. It is too bad that the EGRT(a) sensor is nearly impossible to change without removing the cab and/or all kinds of other gear. Otherwise, it would be a logical next step - replace that darn thing.

Otherwise, my regens (for the 17K pounds I am dragging around all the time) are pretty normal: Somewhere between 80 and 200 miles depending of the type of road/driving. Also, my exhaust is quite clean (at 44K miles). No problem with oil dilution (anymore?) - level remains right where it should.