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2005 Cadillac Escalade ESV 6.0 LQ9 AWD
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Discussion Starter · #1 ·
I have to start with I absolutely love my ESV, she has just over 200K, runs and drives great. Recently I had to replace my knock sensors, and while I was in the engine that deep I did my valve cover gaskets ( had an oil leak due to worn grommits), did plugs & wires cleaned up the gunk from the oil leak and made sure wires, hoses, and connectors were good. Easy peasy.

About 3 weeks later my check engine light returned, OBD scanner showed bad Mass air flow sensor, switched it out and was good to go.

About a week later at fuel up it took over 20 minutes to fill my tank, the pump kept kicking off. At that point I found the charcoal canister had gone bad so took care of that, along with the purge canister and solenoid and cleared the lines from any stray little carbon balls. No check engine light or indication of any issues for two weeks when it was time to fuel up again, still have the slow fuel issue but its not as bad as it was, I can live with it.

A few days after that fuel up check engine light decided to say hello again. I pulled off codes P0171/P0174 fuel trim system lean banks 1&2. Everything I've found on line so far says I have a vacuum leak. I've been trying to pin point for a month where now, no luck. No driveability issues at all, no hesitation when I accelerate, no change in mpg (I have a lead foot so I average between 12.5 to 13.9 mpg in town) no rough idle, no start up hesitation nothing but the check engine light. Honestly this is an issue I would ignore because she is running so great but I live in Cali and I have to smog and cant with the light on.

So today I went to a smog shop told the tech my issue asked for suggestions ideas maybe some free labor, he was unable to find a vacuum leak either, monitored the fuel trim for a few, listened to how it was running and suggested checking the fuel pressure. My LT fuel trim is averaging 20% both banks and ST is between -2% and 1.5% both banks. He was thinking fuel pump/regulator issue. So I get home and check it out and my fuel system is 58 psi, well within range of what it should be ( 60psi +-5) my fuel to air ratio is a steady 14.6:1.

I have reached the end of my mechanical knowledge and as a single mama putting her in the shop is just not in the budget. Please if anyone else has dealt with this issue or similiar or can maybe offer a helpful suggestion on what to check next, or a link to a free service manual it would be appreciated beyond measure. Thank you in advance for any advice!!
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