Slartibartfast

My '95 liked to stick in 4x. Changing the transfer case fluid fixed it.

My '93 has a hole behind the bracket so the bracket and switch from a 94-95 would fit--no carrier light on the dash, though.

Interesting about the trans buzzing. I had the same issue on my '93 recently while I had it all to bits. The trans started buzzing whenever I turned the ignition on. Drove me nuts trying to find the issue until I found the battery was down to eight volts or something (I'd been running the fan, messing with the windows, and testing circuits with the engine off). I charged it back up and it went from buzzing if the key was on to only buzzing key on and throttle open a little like you've got. Full charge, no more buzz. I have no idea if this issue has anything to do with what you're dealing with, but it couldn't hurt to check the battery voltage and condition of the clamps/fuse links/etc. You might also try wiggling wires/plugs under the hood to see if you can make it act up--or clear up if it is acting up. It could be a bad connection somewhere that can't decide if it wants to make good contact or not.

"Honey, have you seen the oven mitt?"

Yep, the gearbox in the Scout snow plow is the same way. If it won't go into reverse, I either let the truck roll slightly in neutral or slot it into first or second.

The holes for the hold-down rods are supposed to be at the front and back of the tray--pull the battery and you should be able to find them easy enough so long as it hasn't been modified by corrosion or a previous owner.

That harness is part of your alarm system. No idea why screwing with that would make it run better.

Is your battery hold down busted or missing? If you're just looking for a "for now" fix you could put a bungie cord across it. A friend of mine's van has been that way the whole time he's owned it. You might also try cleaning the connections where the wiring meets up if possible. Even with the battery shifting around, you shouldn't be losing the headlights like that.

If you're doing it yourself, the writeup on beergarage might come in handy, or at least give you an idea of what you're up against.

My first thought is to look for any trim that might be loose. See if the rubber splash guards (I'm assuming the R51 has those) are in properly. Maybe also look for a plastic bag or something that could've gotten caught underneath. A couple friends and I tried to stop the air coming in around the doors of a van with duct tape once (it's that kind of van) and succeeded in making a very loud buzzing sound as highway-speed wind beat the tape against the sheet metal.

If it came on without warning, or after moving the distributor (or if you check the dizzy and it's loose) then it could be timing. Wouldn't hurt to check the distributor bearings as well, especially with the tach acting up. Anything about how the issue started that might help diagnose it? 55 means the ECU doesn't know there's anything wrong. IIRC if it knows there's a problem with a sensor it'll throw a code and fudge that sensor's output from stored values--you might try unplugging the usual suspects (MAF, O2, coolant temp maybe) one at a time to see if it runs better guessing than it does reading them.

I think I read about running the rear end with diesel on another forum as a last-ditch way to bring back glazed LSD clutches. If the LSD still works it's probably not worth the bother.

Interesting. I guess if the shaft was running around in a flogged bearing, the optical slits could've just been misaligned with the sensor or something.

I was actually thinking they might be directional. I had one to bits before I switched to manuals but only sort of understood how it was supposed to work. The FSM helpfully shows nothing except the bits that stay on the CV shaft, with the rest being part of a (presumably non-serviceable) "assembly." Hopefully the problem will be obvious on disassembly. If not, drive it with the hubs off, see if it still makes the noise... if it does then something else is wrong.

with a million little clips held in mostly by habit, just waiting to go all to pieces when you touch them...

Definitely sounds like something didn't go back together right. Not much to go wrong where you bolted the CVs to the diff, so I'm inclined to suspect that a ) you've got automatic hubs and b ) they didn't go back together right. They'll chatter and grind and generally let you know when they're not happy. When one of mine came half-unstuck it sounded like the wheel was going to fall off. Pull the hubs, see if the noise goes away. If the washer/clutch/snap ring stacking checks out, consider switching them side to side in case you mixed them up on reassembly. I assume they're different left/right given how they operate. Don't worry about your transmission, though, I don't think even the most ambitious of us can stuff the trans or transfer case while doing CV axles.

What makes you think it's the transmission cooler issue? IIRC the Strawberry Milkshake of Death issue didn't start until the next generation with the four liter. Having a mechanic read the trouble codes for the transmission could tell you a lot. I would hazard a guess at a shift solenoid that's gotten bound up (assuming the wiring to the transmission isn't damaged).

You might try running it with the MAF unplugged. The computer should go to to stored values then. If the MAF is reading horrendously out from where it should be, the stored values would be an improvement. If not, I'd guess it's not the MAF. If pulling it does make it run better, it could be the MAF, or it could be going back to open loop and ignoring an erroneous input from another sensor. I've only read about one ECU failure by natural causes (not counting submarine attempts as natural) and IIRC that one was an instant fatality. My money's still on the dizzy.

Without a whole lot of documentation, unreal sounds like a pretty good assessment to me too.

Cleaned a bunch of mouse crap out of the air system, drilled a broken cargo hook bolt out of the cargo area (yes, Nissan, phillips-head was a good idea), wondered why there was fluff in the channel under where the trim goes... spent the rest of the night cleaning out the mouse nest that was in there. The nest itself wasn't too bad, but there's this green putty kinda stuff left behind that's a really bright translucent green and doesn't seem bothered by any solvent I've thrown at it. I can only assume it's what happens when mouse piss meets mold spores. Have I mentioned that I hate mice?

Was the dust in the distributor sort of reddish? I remember reading that red dust in there is a sign of the bushing going out. Given that the angle sensor is optical, the dust could be causing problems. I've also read that a distributor going out will act up more as it warms up. Your fuel pump readings look fine to me. EF&EC 139 says ~34 psi with the regulator hooked up, ~43 unhooked, which is right in with your readings. I think you can rule out the fuel pump.

The thing about going a way nobody's gone is that nobody can tell you what you're in for. IIRC people have done long-travel IFS but usually end up 2WD since there isn't much room for the diff. SAS is more common but quite variable depending on what axle you run, how you match it to the rear, and how you do the suspension. It also depends on what's available in wrecking yards in your area and how much they want for it. Which setup to go with kinda depends on how/where you want to drive the thing. Keep in mind with either an SAS or grafting another rig's IFS into it, you'll have to match the ratio in the rear end (or swap the rear end as well), and if you're keeping the stock engine and trans then you'll need a front end with the diff on the driver's side--apparently passenger's side is much more common.

You want fun? Turn the fan on 4 with the resistor pack out. Leaves everywhere!

31x10.5R15 was a factory size. Never had rubbing issues with them mounted on factory alloys (Legos) at stock height and they don't stick out past the factory flares. I've heard you can go up to 33x10.5 on Legos with minor fender work. If it works at stock height, you should be golden on a 3" lift.

If something in the driver's side of the engine bay is loose enough to bang around, even if it's not causing the problem on its own, it could be setting off your knock sensor. It's just a little piezo deal under the intake manifold that sends a signal when the engine vibrates, so if something's banging around against the outside of the motor, the knock sensor could well be picking that up instead. Good luck!