06/23/2026
The Yukon decided it wanted attention on the way into town today.
It started hesitating, bucking, and acting like it was running on hopes, dreams, and leftover fuel vapors.
I hooked up the ZEUS+ while limping down the road and noticed the EVAP system was commanding the vent valve open, but the fuel tank pressure sensor was showing around -15 inH₂O.
That's a problem, because when the vent valve is open, tank pressure should be hanging out around 0 inH₂O, not trying to recreate the vacuum of outer space.
Fuel trims were climbing positive too, which told me the engine was getting less fuel than it wanted. The poor fuel pump was working overtime and getting nowhere.
I made it to O'Reilly's to dump some used oil, but instead of leaving, I turned their parking lot into an unpaid diagnostic bay.
I started with the vent valve since they're common failures. It was open and flowing fine. Next, I disconnected the purge line and watched the tank pressure immediately return to atmosphere. Interesting...
Then, for scientific purposes (and because I apparently enjoy suffering), I blew into the canister vent line. I nearly collapsed a lung trying to move any air through it.
The charcoal canister was plugged up tighter than a shower drain on Kashyyyk after a Wookiee family reunion.
What's happening is the purge valve is doing exactly what it's supposed to do. The problem is the vent side of the canister is completely clogged. So every time the purge valve opens, the engine starts trying to suck fuel vapors out of the tank, but no fresh air can get back in to replace them. The result is enough vacuum in the fuel tank to make a Capri Sun jealous.
Eventually the fuel pump has to fight that vacuum just to move fuel, and it starts losing the battle. The engine goes lean, fuel trims skyrocket, and the Yukon starts driving like it's offended that I own it.