89 MJ

You are correct. I get why you’re second guessing yourself, this is a super strange issue

Goodness, that's probably what Old Faithful wants to be when it grows up. At least its all rust proofed. So somehow, it seems that the lifters are getting way too much oil or possibly that the lifters are diverting all of their oil up through the pushrods. I'm betting the first option though. Does it sound like it has a lifter tick? Being that it did it with the old oil pump too, I think we can safely rule that out from being the cause. I found this on how the oiling system in the 4.0 works: This has me thinking that possibly the main oil gallery is either somehow larger than it is supposed to be or that the other oil galleries coming off of the main gallery are partially blocked. No clue how that is possible though. How did the main and rod bearings look when you changed them?

I like this idea a lot. And as a bonus, I'd think it should help keep the shop a little bit cleaner too.

I'd agree that the oil pressure seems on the lower end from a fresh rebuild. Might want to check it with a mechanical gauge. Is it a geyser out off all of the rockers or just a few of them?

I would say that is true

There’s definitely something there. I’m right there with you

I also don’t think that the 4.0 is much better than the 2.5L. Certainly isn’t worth the work to swap in a 4.0 from a 2.5L. The only reason that I think would justify a 4.0 swap is if the truck was going to spend a lot of time towing.

That’s what I thought. The vinyl floor trucks seem to rust worse than the carpet trucks, which makes sense.

What is your oil pressure when it’s running?

Could be. Looking closer, I wonder if the gauges are aftermarket ones for something like an 80s F150. And maybe the climate controls are aftermarket like Vintage Air?

Makes sense, this was just the first I’ve noticed it

And the build sheet says 3.55 gears. I thought all 2.5L AW4 rigs had 4.56 gears. The build sheet also says it’s an MPFI 2.5L

I wonder what’s up with those gauges in that MJ

The belt should have less than an inch of movement if it’s tensioned properly. I’d pull the belt off and figure out what isn’t spinning and replace it.

If the belt is on and tight, the water pump and alternator being seized would be my first two suspects.

Hopefully its still fairly solid with the conditions its sitting in. The visor and rain deflectors are neat.

I was told that if its bent tubing, its a header and if its cast iron, its an exhaust manifold. Headers also typically have closer to equal length runners. That's why I call it a header, but I'd guess the parts books call it an exhaust manifold. At the end of the day, I suppose it doesn't really matter what we call it though, they have the same purpose.

This feels very familiar to me. The floors were rustier than I expected. Let me guess, it had a factory vinyl floor?

Yes they can because they have a header and not a cast manifold. Maybe talk to Newcomer racing about the lifters they use. Otherwise, anything made in the US will probably be your best bet.

Sounds like a lifter to me, but I’d make sure all of the rocker arms are tight first. I’ve had a hole in a rocker arm before where the pushrod goes and that was my tick. While you’re in there, you might want to lap the valves and change the valve stem seals. Maybe throw a timing set at it too. Make sure the lifters you get are good quality. It seems that most flat tapper lifters anymore are cheaply made garbage that like to wipe out cam lobes.

The NP242 does throw a wrench into things. Of course, if you aren’t going to use 2 high or 4 low, you could use a NV149 or NP149 which were the AWD t-cases used in GM vehicles in the early 2000s. For long term parts availability, I prefer using OEM parts instead of needing adapters by various companies. With the number of well known adapter companies, that’s a fairly weak argument though. I also want to be clear that I’m not trying to tell you how to build your truck, this is just some food for thought.

I’d find an NV3500 out of an 88-05ish GM truck. Then it’s using all GM parts, none of the fancy conversion bellhousing or anything like that. I do also really like the 700R4, my mom had one in her 46 Chevy and put over 70,000 miles on it with no issues, my brother has one in his J10 that sees off road use and has had no issues, and I’ve got one in my 40 Chevy pickup and it has been fine for moving the truck around for over a decade, but it hasn’t seen the road yet. At the end of the day, I’d recommend using a GM trans for simplicity. Then it’s just your preference for a stick or an auto.

That’s odd. I would think that the pump would’ve run again. I suppose the pump ground would be the first thing I’d check. Good that it started though.

Would it be easier to sandblast it?

That’s always the best way to do it