gogmorgo

The logic I was told is that the water getting pulled through the leak is thicker than air so it momentarily is blocking the leak. There’s undoubtedly some effect on combustion running water through the engine, but mostly you’re noticing the change in airflow into the engine. It’s going to set the idle air control to basically closed with all the extra leaking air flowing in, and when that extra air stops it has to respond by opening the idle control back up to compensate. The intake and exhaust manifolds use a combined gasket. The head gasket is its own thing so no need to worry about it right now. If the manifold bolts have been loose any leaking exhaust will burn holes through the gasket, potentially also on the intake side, so while you might get lucky just snugging up the bolts it’s likely it’ll mean a manifold gasket is in your truck’s future. But the good news is it’s not difficult to change the manifold gasket. All you really need to do is unbolt the manifolds from the head (intake may also be bolted to power steering pump) and push the manifolds over out of the way, get the old gasket out of there, and scrape any remaining gasket off sealing surfaces on the manifolds and head, then put it all back together. Unplugging the injector harness might give you some extra room to work.

Are you at or near full steering lock when it happens, and does it go away when you dial the steering back a little? It’s pretty common for a tire to catch the lip of the lower control arm, especially with larger than stock size tires, but even stock sizes can make it happen with aggressive enough tread. If that is what’s happening, going to tubular lower control arms like the WJ arms might be enough to stop the rubbing, or at least give them something with less bite to rub against compared to the stock arm. My ZJ on 31’s was bad for that, it would turn heads while parallel parking before I swapped the lower control arms. I’ve also had tires catch my inner fenders a little and make not great noises, but the tread blocks catching on the lower control arms can be drastic enough you’ll feel it in the steering wheel.

Air pressure gurgling through something isn’t a particular good tell of whether or not a heater core is free and clear, or if a valve is operating correctly. Definitely not enough to commit to changing a heater core. You can bypass the heater valve easily with some hose adapters. That’ll tell you whether or not it or the vacuum to it is the problem over the heater core. If your weather isn’t cooperating in a way that would let you run a garden hose through the heater to flush it out, you can usually get away with doing it at a wand wash, but be real ginger careful with 2000psi if you can’t get the tip off the pressure washer wand.

You can also just use water while the engine is running to find a small vacuum leak. The rpm will dip while the water is being pulled in (temporarily stopping the leak) and going through the engine, sometimes it makes noises. No harm in doing it either, it’s no worse than driving in the rain. Smoke testing works by pushing pressurized smoke into the system and seeing where it leaks from. Potentially you could do similar with soapy water, but I’ve never attempted it.

Spectra’s a Canadian company. They’ve shifted a lot of production to China but the bigger bulkier things like fuel tanks that cost a lot to ship are still made in Canada.

Blend door movement is visible without taking anything apart. It’s under the dash above the passenger’s left foot. If you peak your head under the dash and slide the temperature lever back and forth you should see the cable moving a little bent rod, the other end of the rod is the blend door. I don’t recommend removing the cable from the rod unless you need to. The valve changed at some point so I don’t know for sure if this is the rule, but I had a ‘92 XJ with almost no heat and patching a vacuum leak in the line down to the reservoir in the bumper brought the heat back. Which was nice cause I was road tripping it at -40 when I found and fixed the vacuum leak. But at any rate that would tell me the valve opens when it gets vacuum. The vent selector kinda worked prior to correcting the vacuum leak, but mostly only at idle.

Bad NSS is a no-crank situation so it’s not that. Intermittent issues are difficult. And there isn’t much that letting the vehicle roll will do that cranking the engine over won’t also do, other than giving it time to clear out a flood, let a hot component cool down, or let a weakening battery recover a little. If it acts up again, try cracking the throttle a little while cranking, then roll in and out of WOT for clear flood mode. It would also be good to check for spark at the distributor, pull the wire off the middle button and check against ground, just don’t hang onto it yourself. You can also shoot a little starting fluid down the intake to see what happens. Just to confirm you’ve got spark all the way to the plugs. I’ve had three issues on my ‘91 lead to similar results, occasional stalling and no-starts where I’d come back a few minutes later and it would start. The first was the bellhousing bolts were loose, which meant the flywheel and CPS weren’t properly aligned. The second was a worn out distributor that wasn’t moving spark through it. The third was a broken flex plate, likely the result of the loose bellhousing bolts, but leading to similar misalignment problems.

I suppose something could be scrambled in the abs computer. If the sensors aren’t quite in alignment due to age or weathering, a hard manoeuvre of some kind might be just enough of push out of alignment to start registering issues. Bearings often end up getting replaced in sets, based on the logic that if one is gone then the rest aren’t far behind. I don’t fully believe in that logic, but if it holds it would stand to reason that failing bearings are happening around the same time. And unless there’s a seal or lubrication failure, you can get away with rolling on loose bearings a long time before something catastrophic happens. The same everything happens equally to everything logic also applies to corrosion, dirt accumulation, anything else that could suddenly get to a tipping point. But we’re all just speculating here. I’ve experience cases where a lost signal makes the vehicle incorrectly think the wheel has stopped while braking, actuating the abs and releasing the brake on that corner, but you’d notice the pull and pedal pulsing.

“Signal malfunction” instead of a circuit code would tell me the sensors aren’t sending useful data, rather than a wiring problem. Meaning they’re not reading the tone wheels properly. That would be a bearing issue, sensor misalignment, tone wheel corrosion sort of concern. The sensors passed the circuit integrity checks but aren’t sending good signals.

Wheel bearings going out at more than one corner, tone wheels rusting and/or packed full of stuff... wiring issues maybe. Kinda depends on what the code is. If it's a circuit code then that would indicate a wiring issue, possibly a bad sensor. If it's an erratic signal it's more likely to be a mechanical issue.

Which end of the harness was wrong? Do you still have your original speed sensor in there or the one off the YJ? There’s a few different part numbers for the speed sensors for ‘91-‘93 and another one again for ‘94-‘96. I want to say I went through this on my ‘91 when I swapped to an NP242 out of a ‘93. I had to reuse my MJ’s speed sensor because the ‘93’s wouldn’t work with the MJ. It might have been a ‘94 though, it was a long time ago. At any rate I remember wanting to use the XJ’s speedometer gear for a better tooth count than my MJ had, but then I couldn’t use it. There was also something about the 4x4 switches that I think is tied into that interim harness, although my memory’s a little fuzzier there, it could be part of the trans harness, not Tcase. The CAD models use a switch on the CAD, but the later models use an electronic switch at the transfer case in place of the big vacuum mess. When I did it I think it took some effort sorting through to figure out what I needed to do, and I can’t quite remember what all I did ten years later, but everything plugged together in the end. But then I was going from XJ to MJ, not involving any YJ parts.

No, I was wrong So turns out it is a four wire, this is a terrible picture but I think you’ve got the right one. The under hood light connector is a two-wire.

It’s that area and that general shape of connector, yes, although I think the four-wire connector is for the transfer case position switch. I thought it was only a two wire connector, but I could be wrong. I think the speed sensor changed from a 2-wire to a 3-wire sensor sometime between ‘92 and ‘95 but I don’t know how that would affect the connector. I’ll have to double check mine when I get home.

It’s a pain, yeah. Every time I do it I think about looking into a remote mount to make it easier. I think sometimes I’ve unplugged the distributor harness to get myself some more room to manoeuvre in my ‘91 2.5, but I do the same as what everyone else is doing, rotate it so it faces up and lift it up through a hole it doesn’t want to come through nicely. The new filter goes back in the same way, usually with some fresh scratches in the paint.

What did you do to jump start it? If booster cables were hooked up backwards it can do interesting things, blow the diodes out of the alternator, pop fuses… I only know this because I’ve had it happen to me so no judgement if that happened. My first thought was battery terminals. Having a battery go completely dead does sometimes cause corrosion on the terminals. The brown wire at the ignition switch is also a strong possibility. If the blower motor was going, as voltage goes down and a motor slows down, current through a motor goes up, and it will find any weak spot in the circuit.