On Saturday, at 330,200 miles, I did the following work on the K2500:
Replaced the O2 sensor. I couldn’t believe how easy this was to do. It’s easy to access and easy to unplug, right next to the transmission.
Replaced the PCV valve.
Replaced the spark plugs, with the new ones gapped to .045″. The air filter housing specifies .035″, but people online said I’d probably experience improved fuel economy with a slightly larger gap.
Replaced the spark plug wires. This was problematic. I should have done one wire at a time, but instead I marked them (apparently incorrectly) with the cylinder number, then unhooked everything, thinking that would be easier to match up the new wires by length. But I hooked everything back up wrong — twice — and upon cranking, the engine was not at all happy. I finally got it right the third time by disconnecting everything again, looking up the firing order (18436572) and marking the distributor cap carefully, and hooking up the wires one-by-one.
Replaced the distributor cap and rotor. No problem there.
Replaced the fuel injectors and cleaned everything well. This was the first time I’ve replaced a fuel injector on any vehicle, and wasn’t hard at all, though you do have to be careful to follow the procedure step-by-step to get the order of seals, washers and o-rings correct. Also, the injectors have to be oriented a certain way or you won’t be able to hook them back up.
This all took about four hours, mainly because of screw-ups. Once I got it all right, the engine fired up just fine. A test drive revealed no difference in power or driveability. I’m hopeful that the fuel economy will improve under highway conditions.