Big Blue: 2005 GMC Yukon Denali

[Jake]

Mileage: 142,800

I decided that I'd take advantage of the oddly nice weather to attempt a few fixes on the Denali before winter really sets in.

First up, while "working from home" last week, was the evap system "vent valve solenoid." I had a code for it and it's $20 from Amazon for an AC Delco replacement. The part is clipped on to the charcoal canister, located above the rear diff and axle. Two bolts let the canister swing down, which gives you plenty of access to the solenoid.

The entire internet warned me about the plastic tube that you have to disconnect and "OMG you will break the clips, make sure you have spare rubber hose and clamps to replace it!!" Well, if you take more of a James May approach vs. Jeremy Clarkson, you can remove the tube and use it again. It's just some plastic clips that need a gentle touch to remove. I used a small pick and some patience and it worked.

The offender:



I cleared the CEL and it came back after a few ignition cycles. Some Googling reveals a second Evap solenoid thing near the throttle body. It's similarly cheap, and people claim that often the truck will throw the code for one when really the other is bad. So, I guess I'll do that eventually.

Next up - the valley pan of doom.

I say that only because this was an intimidating job until I started on it. I had helped Joey work on Lauren's E39 540i as her valley pan gasket was leaking a few years ago. We had to remove all sorts of crap to get at the valley cover, and it still leaked when we were done. So, that was the "experience" I was going in with.

Really though, it wasn't bad. I found a great DIY that showed how to replace the knock sensors, which is 95% of the job.

Basically... remove airbox and throttle body. Drain and unclip fuel line. Unplug injectors (by far the biggest pain-in-the-ass of this entire job). Unplug some other stuff. Unbolt the intake manifold and remove it.



The knock sensors are under these styrofoam-y covers. Pull those up with a small pick, unclip the harness and then unbolt the knock sensors with a 22mm deep socket. Admire the copious amounts of sludgey shit on the valley cover as you do so, perhaps from a leaky valley cover gasket.



Now unbolt the valley cover and carefully (again, use a pick and/or flathead screwdriver... carefully) pry the cover up. It'll probably be stuck due to aforementioned sludge. You may have to find a stepstool to achieve proper leverage when removing the cover:



Odd thing - when I unbolted the valley cover, about half of the bolts holding it down weren't even finger tight! The torque spec is low - something like 10 in-lb - but I didn't even have to use a wrench to unbolt them. Maybe that's why it was leaky.

Death Valley:



Old gasket and nasty valley cover. I cleaned the cover up with Brakekleen and used a new Victor Reinz gasket.



Put everything back together (valley cover bolts are effectively "snug" torque, knock sensors are 15 ft-lb which is also "snug" and so is the manifold. Be careful.), reconnect the various electrical connections and vacuum lines you pulled, and start 'er up.

I'm now facing a fun quirk - the drive to work this morning was my test drive - when the motor warms up, it gets a bit of a bouncy idle (varies by 200 rpm ish) and the dash lights pulse. Kind of seems like an odd vacuum leak, so I need to check the hoses I pulled. Fortunately, I only pulled a few of them so I'm hoping I can find it easily enough.