2.5 Power Loss?

[JYau]

I have an 88 shortbed 2.5 2WD 4 speed. The engine I don't believe is original, it might be from an 86 and I say this because the oil filter thread is an M20 which I thought was for engines 86 and earlier, can anyone confirm? Anyways, I've had this truck for almost 5 years and has always run great, gets good MPGs and power always seemed smooth for a 2.5. I have done a lot of Cruiser's electrical upgrades etc. to ensure the 36 year old truck continues to run strong. However, today when I was driving it down a 45-50 MPH road the truck started to randomly drop power almost to the point where I though it was going to stall, it's fine at lower RPMs but 2.5k and up it begins to drop very quickly. It might seem to get worse when it's warmed up because one my ride back home after the truck sat for 30 minutes, it didn't start having problems until after a few minutes of driving. The issue seems to only happen under load, with it sitting in neutral I can rev the engine up and hold it there and it seems fine, but this is just a small test

 

So far from what I gathered online, it could be fuel pump issues, MAP sensor, O2 sensor. When I first got the truck, it had a new fuel tank and pump, and I have changed the MAP and O2 sensor just a few years ago. Also, last year the CPS sensor was replaced. The truck starts up perfect every time and idles nice and smooth. Power and acceleration are all normal except when the RPMs and power drops out. When it drops out it bounces back immediately and sometimes will happen a few times and then stop for minutes. I've attached a video for some more context. 

 

Anyone have any ideas on what to check? Thanks!

 

 

[eaglescout526]

7 minutes ago, JYau said:

engines 86 and earlier, can anyone confirm?

Can confirm. AMC used SAE threads up until probably 86 when they changed. I thought all the 2.5s were the same until I went to change my oil filter on my 84 and it was a different size. So 86-90 use the Renix Metric size. 
 

I’ve had my TPS do the same thing except not totally drop out but just stop keeping up and then come right back and be fine for a little bit. 
 

I’ve had fuel pump be fine until it gets warm and it basically won’t be able to keep supplying fuel until it stops and you have to reprime the pump to be fine again until it repeats. 
 

Issue sounds fuel related but luckily all the sensors can be tested with a VOM. 

[JYau]

I took out the TPS and tested it, seemed to work normal and was steady. It would swing from no throttle at ~3.85V up to 11.8V at full swing. Any tips on testing the fuel pump?