This is my first post, just joined after I bought a 90 Pathfinder XE auto a couple weeks back. I actually have two I'm fixing, I bought another last weekend (91 SE manual) for parts, lsd, etc. but it's in better shape than the first, except:
It ran fine to drive on the trailer. Upper end rattle, the PO said the oil pump went out (how hard could an oil pump be, said the new Pathfinder owner) and there may have been overheating as it was driven until it stopped running. No lower-end noise when running, just upper from no oil. Many, many, many hours later the new oil pump is installed and working fine thanks to much help from this site. Old one was rounded by the crank and shot. Changed the timing belt while I was in there, all sprockets and marks lined up, engine @TDC #1 Cyl verified with the pencil test, marked on the distributor, etc.
Fired it up, black smoke from exhaust and runs like @$$. Won't stay running at idle or if I let off the gas, but when I floor it it's got power. Compression is exactly 122 in five of the cyls, but 110 in cyl #3. Added oil and #3 came up to 122. Looks like maybe the ring in Cyl #3 is going, but I can live with that until a future rebuild.
What I can't figure out is, is 122 too low for the compression? It's consistent, so if it's low then my guess would be timing belt is off. If my timing is off would I see the black smoke? Other thoughts are coolant temp sensor, as the gauge in the dash doesn't move at all. No other symptoms of a head gasket, and I've never seen one blown where all the readings are the same - I almost thought my gauge was going out they were so close. Any help you can offer is appreciated... Thanks!