Originally Posted by
EagleMark
GM service manual says between 9-13 PSI!
Yes it will run between 9-13 PSI.
Most stock trucks I have checked over the years are 12. I can tell you from tuning that even a bone stock truck runs so much better at 13 PSI. At 10 PSI the BLMs are very high...
Have you checked voltage AT fuel pump? Ground at frame off fuel pump? Low voltage at pump = low pressure. But your saying that disconnecting the altenator makes BLM 128 which is better? Makes no sense? If you can do this again when looking at data see if the data shows it is still in Closed Loop! If not in closed loop the BLM will be 128... usually...
I'm only guessing you have no error codes set? As that would be first thing to check and some how you are seeing BLM data.
When you see the INT/Short Term Fuel Trim go red, it is just the program warning you the numbers are getting high. For the BLM/Long Term Fuel Trim 155 is still within boundaries of the ECM adjustment to fuel, IIRC the max BLM in ASDU is 172. So really not a big thing and if you were not a GearHead you would never know. But you are also experiencing a surge, so you can feel something is wrong.
Hows the truck run if you disconnect the O2 sensor and drive around?
A vacuum leak is extra air that the O2 sensor see's as lean and adds fuel, even though it is not needed....
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