GTSBoy

Look, there is no way, no way at all, that you have an interconnection between your PS system and your AC. So just put that thought aside. The PS pump is the top one. The AC compressor is the bottom one. You cannot mistake them or their hoses. I do not understand what you mean by "tiny as metal needle". Is that "tiny as" as in "tiny as f**k?" And then "metal needle" as in what looks like an electrical wire poking out of a bit of conduit (in both photos)? I mean, it's clearly a single electrical wire, connected to a loom plug....on the AC compressor? I'm not that familiar with what that connection looks like, even though I had that part of my car (Neo25DET) partially apart today - I wasn't looking there). It could just be the clutch signal wire for the AC. The AC comp could be covered in PS fluid because....it is underneath and oil drips down.

According to the photo, the start signal wire would not have a ring terminal on it. It would have a normal push on spade socket (the spade itself is the terminal on the starter solenoid). Anything with a ring terminal would want to be the main, big, fat wire that actually carries the many many amps that run the starter motor itself. In that photo, WS appear to be providing a pair of fat wires to the starter, one from the alternator output and one from the battery - effectively making the connection between the alternator and the battery at the starter. I dunno. Maybe this is the way it is done with vehicles with the battery in the boot (because the batter wire comes from the rear, under the car. But I think on front battery cars the connection is typically direct from alt to battery. The battery to starter connection is also direct, so the common point is at the battery, not the starter. Either will work, but the loom really should reflect the chassis as well as the engine.

Yup.

Has no effect on the steering itself. Is for idle control.

Just join the 2x hoses together there, or at the other ends. You will lose the idle up, but it should be fine.

P plate turbo (actual Hi-Po vehicle, not "turbo" as in all small shitboxen are turbo these days).

You're not getting an exemption. They say it is possible, but in practice you will be bleeding out your arsehole by the end of the process (and still not have it).

No. The opposite. Life sucks when you remove it.

Yes, the fan shroud.

Meaning the recirc temp sensor? That was my thought also, except that I thought that was 2pin. Hadn't had a chance to pull ash tray out to have a peek.

Sounds fine.

Is it factory looking? If so, have you looked at the wiring diagram?

I've just had the world's best bad idea. We have fuel returning back to the tank. Just point some/all of it at the inside of the bulkhead fitting. Direct liquid cooling!

Hypothetical hat on.... I think they want to make sure that it is no more than 8.2mm to ensure that the 14mm hex electrical isolator washer thing stays outboard of the hole, so the o-rig on it seals properly, and they want as much room as possible between the passthrough bolt and the plastic lid, so that it can't touch the plastic and heat it. Even assuming that the steel should run cold enough to not be an issue, they are probably applying additional paranoia in case of the sorts of crimp/terminal problems we're thinking might be at play in your situation.

Not more than 50°C. Anything you can't touch is putting up more of a fight than it should be.

Bah. That bit there can't be more than 0.5mm thick, and only about 6mm wide. That's only 3mm2 XS area**, which is a lot smaller than any other part of that circuit. (Although, granted, the wire inside the tank on that blue ring crimp looks a lot smaller than the wire outside!). The equivalent neck on the blue crimp has to be even smaller. **And yeah, I realise that 3mm2 should be able to carry ~30A. But something has to be the weak link here, and that is the narrowest part of the whole thing. So, unless the crimps are bad and causing high voltage drop, the next most likely suspect has to be the necks. The face area of the ring onto the passthrough's landing would have to be multiples of the neck's XS area. So long as they started out tight they (the ring contact face) never should have been the source of the heat. Same with the suspicion of the possible nyloc. If it started out tight, it shouldn't have ever gotten hot enough to melt the nylon, loosen and then cause the heat that melted the nylon. The circular argument has to start elsewhere. If it were me, I'd be thinking about some other sort of passthrough that doesn't require the nuts and ring terminals for conductivity. If there were passthroughs that had direct crimps on both sides, they'd be single use, but they would have metal to metal interfaces only at the crimps. Would be solid metal between the crimps.

I'd try the Jaycar one first. Don't even bother with replacing the passthroughs, as they will still work provided the melting is only minor and they still seal and insulate. You can always go back and replace those later. After you've put the new crimps on, you just have to make the pump work for a bit, then go back there and laser gun the terminals (or touch if you're brave enough) to see if they are sufficiently cool to relieve your concern. You might want to gather a data point with the old setup first, to see how hot they get now.

Yeah, see, I think I've worked out what is happening here. You (and other people) buy these massive "40 amp rated" pass throughs, and use fat wires, then make the connection between them using a ring crimp that has a much smaller cross section in that piece in the neck between the crimp and the ring terminal than any other part of the system. And it gets hot there. And because it is very well connected to the passthrough....that gets hot too. We probably need to be using more chunky wire terminations.

I'm thinking that if it is struggling to make boost....the turbo is damaged.

I don't know. Look at the wiring diagram?

You can't do a really convincing examination of either the valves or the pistons (through the plug hole) with an endoscope. You can have a look, but it is difficult to see everything.

Both the black plug (red/white/black wires) and the grey plug (yellow/green/brown wires) go to the location at the front of the plenum. I didn't recognise the wire colours in your first photo of the grey plug because they are so dirty.

What Josh was saying is that the stock gauge reads dead on centre across a really wide range of temperatures, from "not quite up to operating temperature" all the way to "you're just about to cook it". That means that if you ever see the gauge over the 50% mark it is actually very bloody hot, and yes, you might have done the gasket at that time. Or, you might not. Head gaskets can fail so that coolant enters the cylinder, exhaust gases enter the coolant, oil enters the coolant or water enters the coolant, or any of the possible combinations. Just not seeing emulsified oil in the radiator is not sufficient to rule out gasket failure. You also need to test the coolant pH, to look for dissolved combustion gases (CO2 -> carbonic acid when dissolved in water). A fluffy idle could be from a dying/dirty injector, dying coilpack (or perhaps damaged sparkplug), a vacuum leak on the inlet manifold gasket, broken piston/ringlands or burnt exhaust valve, and any of a number other things. You need to start working through the list.

OK, so after a closer look at your first photo I realise that while the body of the TCS throttle is present, the motor isn't really there and it looks like the TCS TPS is not present on the back. So you should not have any wiring coming out of the three bolt cover on the front, or on that block of alloy on the back. That leaves just the main throttle body (the part closest to the plenum). To the best of my knowledge, the main throttle body and its TPS is the same between TCS cars and non TCS cars. What do you mean by "the throttle body has two plugs"? The main throttle body TPS in your photo clearly has one bunch of wires coming out the TPS on the front, and these should go to a loom plug at the front end of the plenum, as I described above. You show that grey plug with 3 wires, but you do not say where those wires come from, apart from "out of the throttle body". But where on the throttle body? Are you sure? As to the driving behaviour. Are you running >10 psi? The stock ECU will chuck the shits at you based on the inputs from a number of sensors (the AFM and the boost sensor primarily) if it thinks you're pushing it harder than Nissan wanted, which is not very hard at all. If you are, you should really have Nistune in the ECU.

FWIW, I got about 20 out of the RS4s. I liked them....until I didn't.