Long story short, my LTFT on both banks when driving normally are +20-35%. I was able to do a WOT test and confirm that there is a vacuum leak somewhere due to the fact that LTFT drop to +4%. Once and a while, it pulls P0174 & 171. I bought the car from my mom (who was the original owner) and I think at around 170K Miles, she blew a head gasket. Considering the fact that she got the car fixed the same day she brought it in, my guess is that the shop she brought it to, used a head gasket maker as opposed to installing an OEM gasket. I decided to change spark plugs to see if that would fix the problem. If you don't know all ready, you have to pull everything from the intake box to the manifold to access the plugs facing the firewall. As well as removing the wiper blades and hood cowl. I visually inspected everything to ensure there was no cracks or tears in the induction systems. I also checked the PCV valve (which was fine). However, at the time, I didn't think to inspect around the cylinder head. If its not obvious, changing the plugs didn't fix the problem. I also had the cats replaced at 180k. I also tried using smoke to visually look for looks. I also bought a new MAF sensor to see if that would change anything. I have done almost every possible inspection I could do. So I have a couple of questions.
1.) Could a faulty head gasket cause high fuel trims? And no, there are no visual coolant leaks
2.) Could clocked injectors cause this? In my opinion, I don't think it could be injectors because the ECU has no problem adding fuel to compensate for the lack of fuel/high LTFT
3.) Do I need to re-flash the ECU/PCM?
4.) Could it be the upper windband sensors? They have never been replaced. However, I have replaced the lower O2 sensors
As of today, 01/13/22, it is pulling a catalyst below efficiency threshold (bank 1).
