178k miles. Has an aftermarket intake tube and Doug Thorley shorty headers that have both been on 7-8 years. Replaced the Y-pipe and catalytic converters about 3 years ago with a crappy Walker replacement (works, but doesn't seal well on bell & spigot joints). Changed the water pump last fall when it started leaking. Otherwise it's just been regular maintenance.

Recently started getting short term fuel trim CEL and then occasional misfire on Cylinder #7. It runs OK when loaded, but the short term fuel trim goes to max at idle. I did a compression test yesterday and have 2 cylinders below spec and #7 is below 100 psi. I broke out my leak tester and tried it on a good cylinder to make sure it worked. I then used it on #2 and #7 and confirmed the leak-by, but couldn't hear anything from the open throttle body, open oil fill cap or out the tail-pipe. I had noticed that the ceramic coating on the headers had been coming of the #7 runner and suspected it was because it was near the battery, but now I suspect a leaking exhaust valve.
I'll take it to someone that is more equipped for checking it out, but I'm not optimistic. The truck is still in good shape otherwise, but I'd lean more toward a low mileage junkyard motor or rebuilt long-block rather than tear into this one. I think the trick will be finding one, as they changed in '08. Any words of wisdom?

 

I think you're on track with the exhaust valve. Wonder if it dropped a seat or burnt? Too bad ... Either way, it needs to be fixed. I would go for the reman with warranty.

 

these trucks are famous for dropping into the #2 cylinder. mine did at 217000 miles,

 

Thanks for the info!

 

Got the heads rebuilt, including new hardened valve seats in place of the powdered metal seats. When I pulled them off I had a couple seats that looked rough but none that had come loose. First fire was yesterday and all is good, other than an exhaust leak from my crappy Walker replacement catalytic converter/ Y-pipe. I'll work on that my next day off and get a few miles on it before doing another compression test and leak-down test. I made a ring leak-down tester with a 6" square piece of 1" thick aluminum plate. Drilled 4 holes for head bolts, one spark plug hole for the leak-down tester and gasket material glued to one side. I bolted it to one cylinder at a time and used my leak-down tester to check each cylinder in turn while waiting for the heads to come back. I had some variation but nothing that worried me. Since I had it all apart I also replaced the timing set and the front main seal. I wasn't super excited to tear into it, but I didn't want to buy a junk-yard motor or a rebuilt long block that still had powdered metal valve seats.

 

How did the #2 and #7 valves look? No burning?

 

#2 and #7 were cut/burnt but weren't loose. #7 had thicker deposits on the intake and exhaust valves that looked like a coolant leak, but there were no tracks on the head gasket or sealing surfaces and I've never had to add coolant between changes. EGR comes from #7 so that may have something to do with it.