Commanded fuel pressure stuck

[windowrattler]

Figured I'd update this post. We did fix/tidy up the can network. Still was having an issue. Was able to catch the fuel pressure going into the negative reading when the hiccup happened in the drivability. Well there is no way that the negative reading was correct so we put a fuel rail pressure sensor in it. Still had the issue going on with commanded staying at three levels and actual staying constant at 13k no matter what was commanded.

So what I was seeing the symptom not the cause of the issue. I was assuming that the difference between commanded and actual when "stuck" was tripping the 1911 code. What was going on was when the under full load fuel pressure would be fine at 37k when you go to shift you get a small increase in fuel pressure to about 39k when the injectors shut off for decel. The fuel rail pressure relief valve was opening at that 39k dumping the fuel pressure too quickly down to about 13k. The ecm would then go into a protect mode which keeps fuel pressure constant and commanded at the few different levels. After a little bit the ecm will "reset" the fuel pressure which causes a short engine cutout, fuel pressure sensor will cycle (where my negative numbers were coming from) and it will start operating 100% correctly again until the next time the relief valve opens. After the replacement of the relief valve fuel pressure doesn't dump at a shift like it was.

The code we were getting was 1911 and eventually a 3727 (which helped us look at the data more correctly). When 1911 is active that is what makes the fpr "stick" in some default values/limp mode until it resets itself and returns to normal.