Hi, I'm new. I'll introduce myself. I drive beaters since they are not expensive and often easy to fix. Current truck is B2200 Mazda that hit a small deer, then a phone pole and I got it for parts, only to break the heat sensor off the rad by accident, which actually fixed the truck :). The fan started running all the time and the quick JB WELD rad fix has lasted. I am driving it again as my other old Mazda, backfired and blew the timing belt. I had driven it for 3 years for a $250 investment, so not worth paying more than double to get it fixed. The accident prone Mazda I'm driving now has manual steering and it's not for me any longer, except for emergencies. so.... end of introduction and on to the ranger question.
I found a 1991 Ranger 4x4 auto trans. Apparently It has an engine knock... all else okay LOL except the hubs don't work. I have an old 1989 Ranger that broke in half (luckily not on the road). Its been sitting for quite a while. Yesterday I checked the VIN and it has a 2.9ltr 6 cylinder motor. The motor was good and also had auto trans and power steering,(it just rusted out). Same motor as the 1991 for sale. I looked up on line about engine knocks so I would understand a bit about it and then just called the seller of the 1991. He said that the oil pressure stays up for about 20 minutes and then it loses pressure...... I don't know him. So I asked a few other things and then he said he thinks it might be the connecting rods. I was thinking about having someone look at my old motor that I have and thought about maybe an engine swap. I looked for an engine online and the wreckers showed that they should be interchangeable.
Q.1 What could cause the oil pressure to drop after 20 min of driving with no actual oil loss (maybe it only happened once, I forgot to ask) and could it be a connecting rod problem? Q 2. If the engine is a write off is it a huge big deal to swap it out for my engine... Any thoughts? thanks, Neddy

 

Welcome to the forum

Engine "knock" can be a few things but if it also looses oil pressure then its for sure a bearing issue
Yes, could be connecting rod bearing or a crank(main) bearing, no they don't leak oil, they just loose pressure which causes other bearings to fail
So yes that engine is not going to last long

1989 to 1991 2.9l engines should be a direct swap, wiring harness on 1991 should just plug into connectors on 1989 engine

Same for transmissions both will be A4LD automatics so plug and play for wiring and bolt up to engine and frame

It depends on your idea of a "huge deal"..............
There are many videos on pulling and installing engines, even some for Ranger although its pretty much the same for any engine swap, or trans swap
Take LOTS of PICTURES, they are free, so you know where wires and hoses connected when removed, you can label as well
There is no specific knowledge needed, its all just wrench work and common sense

You can rent engine hoists, or buy one used then resell it when you are done with it, that's what many people do so they are always coming up on craigslist or ???

One heads up, the weight of the engine is what is compressing the coil springs, the suspension in the front, so when you start to lift the engine up, the front of the truck ALSO comes up, maybe 6-8 inches UP, so you need to make sure your engine lift can go high enough to clear the rad support to get the engine out
If you get into a jamb or don't think you will have enough clearance, remove front wheels and lower front of truck down on to blocks

You can pull engine and transmission at the same time, but should have 3 people, one under, one running the lift and one watching and guiding engine and trans