Thanks for the reply, Mooseman,
The 07 trailblazer has 262,000 miles on it. I am the original owner and have always done the oil and filter changes as soon as the reminder light comes on. About 2 months ago, I removed and cleaned the throttle body for a low idle rpm code. It was pretty dirty and gummed up. Problem solved. About 3 weeks ago, I had to replace the thermostat (stuck open) because the engine was running cold and set the CEL. Other than that, it has been completely trouble free until last week. On my way to work, it took a long time to accelerate to highway speed and it just didn't "feel" right to me. I then noticed the oil pressure gauge was wavering and briefly dropping to zero and jumping up to 40+ again. I also had more engine noise than I usually do. I got off the road and checked oil level. It was low, but only about 1.5 quarts. In the last couple of years, I don't get 4 quarts out during oil changes anymore. I assume its burning a bit by now. I had it towed back to my house and found I had a P0017 active. I cleared the codes and started up in the driveway. Was hard to start (never was) but when it did, it idled OK with oil 40 psi. I didn't want to drive it in case the 0 oil pressure was real earlier. After 2-3 minutes, it faltered and stalled. Wouldn't re-start, just cranked. I'm thinking the low / no oil pressure is real and the P0017 is a result of that. What I find strange is the sudden onset of this, the day before, it ran like a champ. Can a timing chain "skip" a tooth ? And what is a "case relearn" that I see mentioned. How bad a job is it to replace the oil pump in the 4.2L, if it comes to that. Maybe cleaning the pick up screen ? I am not a motor head, per se, but I have no problem getting my hands dirty as long as it's a job I can do.