Car is '84 Z28 H/O 4AT, all original. ~60,000 miles

The car had been sitting for about 5 years. I believe the previous owner had overheated it a few times, as fan doesn't kick on (busted relay I'm guessing), and the cooling system was pretty beat. I replaced the head gasket which was warped. During the job I cleaned out everything at the top of the motor and adjusted rockers. Some sludge underneath the intake near the lifters, but nothing crazy.

I've been driving it around the block since then periodically, as I've been waiting on antique tags and insurance. I'm a young guy and I work as a tech, but I don't work with V8s or older cars that have huge issues like rod bearings or detonation (replacing the head gaskets was the biggest job I've done, though I had help and I'm sure I did everything correctly). And I'm not totally sure what a misfire sounds like on an 8 cylinder (only a 4cyl).

It is very possible the sound was there from the beginning but I never noticed it. The motor has some lifter tick on startup, so I'm not confusing the noise with that (as in there are 2 distinct noises). Standing in front with the hood open I can only hear lifter tick, but moving towards the side of the car right before the doors I hear a slight, deeper tick. The exhaust has a rattle. I put a broomstick to the oilpan and put my ear up to it and heard some slight scraping and chugging. Additionally, when I start it, the starter hesitates, almost like it's trying to move a melted bearing.

The car does hesitate a little when in gear, but I figured that was older tranny fluid. When revving it backfires sometimes when letting off of gas. Just now when I was listening with the broomstick the check engine light came on (I do not have a scanner). I only put 91 in it and emptied the fuel tank before starting it. Haven't rebuilt carburetor.

I haven't done anything stupid with the car and the oil has been changed and is at a good level. Oil pressure is pegged but I figure that is a bad sensor. Perhaps pressure was low and I didn't know. The distributor and wires are old, perhaps leading to misfire.

Apologies for the long post. I am out of my depth, and just did a (by my experience) huge job with this thing and I really don't want to do a full rebuild. And expertise is appreciated.

 

Nothing wrong with a longer post, since the details can be important.

The lifter/valve train noise could be an indication of low oil pressure or poor oil delivery. That same issue could be affecting the oiling to the crank, and thus the potential rod noise you might be hearing. The noise could also be the result of a dead cylinder from misfire, and there are several potential causes for that.

The biggest concern is the oil pressure. If the gauge is at the "0" position with the engine off and goes full-scale when running, it is possible that the oil pressure sender has failed, causing a pegged gauge. It's also possible that a restricted oil passage is actually causing high pressure. Your mention of sludge in the lifter valley might be a hint of further sludge in oil galleries. The indications off overheating (warped head) might also point to a lubrication problem.

Temporarily connecting a pressure gauge would be my first action to see exactly what the pressure is. That should be done before running the engine much more to avoid any potential further damage.

As for the error codes, this version of pre-OBDII control does not need a scanner to retrieve codes, just a jumper. The instructions have been posted here literally hundreds of times.
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