I noticed enormous fuel tank pressure yesterday. And it lasted for quite some time after shutdown. All the hoses are clear and they are clear to the tank vent line as well as I blew air through them and could hear air come out the tank, enough to move a rag on the full neck. Did the evap test per the service manual and was failing the 10 HG vac test on the solenoid with the ECM grounded via AB on the aldl. Putting batt voltage directly to the solenoid made the system work. So the ECM wasn't providing a ground. I could see 12 volts on a meter but not enough to power a test light. So I ran a wire direct from the ECM pin, GRN/YLW wire and still got nothing. I think my ECM driver must be fried. I also noticed that the solenoid can get hot to the point you'd leave skin on it. Wonder if that caused a driver failure. And does anyone have a 1227165 ECM

 

I have a few 165 ecms , used and refurbished.

 

May have been barking up the wrong tree. For ****** and giggles I plugged in the factory blue EPROM chip and the system tested. Something must be up with my tune. The T103 CCP %DC table is 99.61% across the board. I think that's keeping the purge solenoid closed. The stock ARAP bin is 0 until it gets to 24 grams. Glad I checked this.

 

Oh wow, I woudnt of expected that. Good find

 

Not sure why it's not testing with AB jumped though. I don't know where on the EPROM that takes place. I'm thinking that my solenoid is actually getting commanded while it's running but seeing as it was skin burning hot I think it's being commanded closed and held closed which would explain the hot solenoid. Which would also be why the tank isn't venting. I can hear gas burble in the tank. Yesterday there was a good 15 seconds of air coming out of the fill port. Put the cap back on and I could feel the pressure as I tightened it. That's a lot of pressure with nowhere to go because to make matters worse, GM's logic was to keep that pressure in the tank on shutdown and let it release very , very slowly through 2 restrictions. One at the tank vent and one at the control valve. So if while driving that solenoid is commanded shut then that means pressure is constantly building with nowhere to go. I'm going to copy the ARAP table for that CCP and Flash the chip again

 

Wanted to update my findings in the event others are experiencing this. The BBK 52MM TB is the issue. It's so poorly designed on the vacuum side that there's zero ported vacuum. The 6E mask diagnostic test is different than the 32B. AB grounded does not force the purge solenoid to close. On the 6E the purge solenoid has 12 Volts at key on. You then ground AB and it drops the voltage so it's essentially backwards. That was the first confusing thing that was rectified. The bigger issue was the BBK. There is no vacuum on the ported fitting. Therefore there's no vacuum to the vac control and purge control valve. So the solenoid can energize until it's blue in the face and nothing will leave the tank. Moved the source to manifold vacuum, made a few minor changes to enable parameters in the BIN and all is well now.