Truck has 220K miles, doesnt smoke, good power, etc..When cold, and you start the engine, theres a minor "tick" that lasts about 45 seconds..The oil pressure stays around the low side of "N" on normal..Does this sound like a oil pump problem?

 

I'm not an expert on the 351, but if you have low oil pressure, I suggest that you switch to a thicker oil. Try it for 1 oil change and see if it fixes it. Go to 10W40 or something.

 

currently running 15w/40..The guy I bought it from said he had been running that...

 

You can try going to 20W50 if you want to, but I wouldn't use any thicker oil than that. Try switching brands. I like John Deer oil the best. It's cheap, and my truck doesn't burn it like it did every other brand I tried. You can pick any brand you like. Just switch until you find one you like, and stick with it.

 

Most importantly: the gauge is a total fake. It's designed to show mid-scale any time the pressure is above 6 psi. Don't trust it for anything. If you want to know the pressure for sure, buy a cheapo gauge from a parts store or WalMart & temporarily install it. Just let it rest on the engine.

Also, I wouldn't run 20W50 anywhere north of Mexico, this time of year. It's too thick, even for a worn-out engine. Where are you? Put it in your profile.

This may start another $#!+storm, but I'd recommend a good engine flush, following the instructions precisely. Even better, find a shop that uses BG Products & pay them to do it. Be prepared for ~$100 up front, and then a couple of extra oil/filter changes in the near future to get any chunks out. WORST-case, your engine might look like this inside:



It's not too hard to pop the L valve cover off & take a look, though, so consider doing that.

Lastly: I highly recommend converting your oil pressure gauge so it actually works. The new parts cost less than $20, and it only takes ~1 hr to do, including soldering the back of the cluster. It's not calibrated, so it'll never show THE pressure (numbers), but you will be able to see if there's a rise or drop from your normal reading.

.

While you have the cluster out, you might also want to add a low-fuel light, but that takes a lot more work, including drilling the gauge face.

 

Wow! He must have used dirt as an oil additive!!! The only time I have ever seen an engine do that, is if they are full or water, or cheap synthetic oil.