I have a 1994 gmc suburban c1500 with 240000 mils.

At about 230000 miles (once the engine was fully warmed up) there was a loud knocking going on in the engine bay and the oil pressure would drop super low and the idle rpm. My wife had it inspected by a mechanic who claimed it was a rod knock.

Now, if that were true that would definitely suck, but I do want to rebuild the engine anyway. I didn't believe the diagnoses because the truck runs amazing, considering the miles.

I replaced the plugs, wires, distributer cap/rotor and oil pump. After this the knocking would only happen after about 30 minutes of driving at idle, in which the idle would be almost nada, which lowered the oil pressure drastically.

I inspected the vehicle with the knocking going on and located the source, it was a cracked motor mount.

I highlight this because I don't seem to find people checking for that online, but I do see a lot of people with various knocking issues. This is the one I had. Also I did have the engine rebuilt anyway, since it definitely could use it in order for me to get what I want out of it.

I am getting headers, cat, catback, an intake added soon after completion of rebuild. At this point I will test, then post on this site the hp/torque and my observed fuel efficiency.