dbm7

Ahh...should have been clearer ~ there's 2 ... SMJ = super multi junction (connector)... ...this is connector 6 & 25 in above image -- body harness to engine loom (6) & body harness to main loom (25) Headlights go to front via connector 6 ; fuel gauge goes to tank sender via connector 25 ...like I say this is R33 diagrams, but at a pinch R34 won't be too far different. *IF* the two ground faults are related, this can be the only place where both wires converge (as one runs to the back, the other to the front)... ....thing is, you probably need to establish if the faults are related (unless you examine that area and find obvious chaffing on the looms there to body ground)....*IF* the fuel gauge is still broken (full needle deflection), I'd be headed for the boot, remove fuel sender wire, key on and measure the voltage there ~ it should be roughly 10volts. If that's ok, check sender to ground resistance...if this is a dead short to ground (and there's fuel in it), then sender has failed or something funky has happened to wiring in the tank. edit: ahh...rereading the thread, this is R32....above fuel sender test still valid tho'

Correct ~ fuel gauge receives power (usually about 10volts) from a linear regulator on the cluster board (gives a stable reference voltage), and as you say, via a variable resistor to ground (float level) ; high resistance when tank empty, a low resistance when tank full. As you surmise, if the fuel sender wire was shorted to ground, there'll be full defection of the fuel gauge needle. I haven't got an R34 wiring diagram, but going by the R33 spaghetti schematic, about the only thing common here between headlight & fuel gauge circuits is the SMJ connector...

Yeah, R34 with RB25DE likely has a 4AX01 box in it, which is a medium duty auto ~ with the RB25DET mill, it would've been fitted with 4AX00 (4AX13) heavy duty build (same case, different internals). An RB25DET will lunch on a medium duty 4R01 auto in pretty short order ...to give you some visual idea of differences between the 'medium' and 'heavy duty' boxes, you only have to look at the 2/4 band for comparison...it's chalk and cheese...(plus bigger high clutch, extra pinion in the planetary sets, higher oil pump output, different bearings, higher TC stall speed )... You can control them with just about any aftermarket TCU for electric-over 4-speed with TC lockup clutch (ie; the GM 4L60E and others)...I have a custom standalone TCU that includes MAP sensor (for turbo applications) along with TPS, RPM, and line pressure monitoring...in other words, I don't use any ECU signals...no real need to.

Very unlikely...

He's right ~ there is no 'magic' with stuff like this ... it is more likely that in the process of looking for the short, the loom/wire 'incidentally' got moved in the process, thus removing the short ~ now, that maybe a wire (in a loom) rubbing against the edge of some grounded metal, that's worn through the insulation, causing the (now intermittent) short to ground. If one wire in a loom has been damaged in this fashion, it's reasonable to presume that other wires beside it may have also be damaged, and now exposed...you can bet the green crusty copper corrosion will start... ...that'd be a pisser, Murphy's Law steps right in as GTS observes...but worse, something like that is easier to find when shorted...ie; unplug bulb and fuse, and put multimeter in continuity mode so you get constant beep, and carefully poke about hoping to find if some movemet of the harness stop the beeping.... ...it's still all a bit Arnie tho' ..It'll be back... 😃

...yep, in the dark of a wet rainy night most likely 😃

Yeah. air pressure leakdown test is where I would be headed next here, using one's ears to determine whether it's the valves or bores/rings leaking...

Duh... to answer my own silly question, it's actually described in the FSM... ...400 pages away at the end of the manual, for RB25DE/DET signal descriptions, it cites the TPSwitch signal action, is dependent on the TPSensor value ~ this tends to infer the builtin POT voltage signal is the primary, and the switches are fallback/secondary should the POT fail/TPSensor signal lost (and switch alone with no TPSensor signal allows for base idle speed setting).... makes sense... they (TPS units) used to fail/wear the POT with time, they're not exactly built to last ~ having the switch as a redundancy gets around this...(or, it's less likely both signals would be lost as they're on different power rails)... and of course wrt RB26DETT, you have to electrically disconnect the IACV solenoid from the harness, to defeat idle air control...

Same thought crossed my mind ~ depends on how one connotes 'stalling'...ie; gets a rough/stumbling idle as it get warm until it stalls... or... idles ok and simply falls-over when it gets to temp... ...you can test the whole circuit with a couple of resistors ...unplug coolant temp sensor, bridge terminals with a 2K7 resistor (ECU will do cold start), or with engine warm bridge with a 330R resistor (ECU will consider engine to be at normal operating temp)...it's a quick way to check wiring integrity/ECU response when you don't have a multimeter handy ...

For sure the later RB26 variants had a different setup (6 cam voltage sender?), but the RB25DE/DET share the same ECU pinout/PCB footprint, and at the ECU plug it ends up being 'throttle sensor in' & 'throttle sensor out' (to A/T TCU) ...you stick a multimeter on these pins and you'll find them directly connected (0 ohms) ; I had an pair of Nissan ECUs on the bench long ago, and I noticed this throttle sensor in/out link, actually linked to an op-amp ...which was unpopulated on the NA board, but present on the T board and I went 'ah-ha!' in some moment of clarity... ...it wouldn't surprise me if they changed strategy here though (in the software and actual monitoring of this signal), because they did with other stuff (A/T signals).. and 0.45v as a trigger point makes sense, as that's what the external TCU units expect at idle ; kudos, thanks for that insight...I suppose it boils down to whether or not Consult can display real time data of that signal's voltage... ...in any event, it presents the same target...ie; rotate TPS unit to achieve 0.45v to suit both ECU&TCU, and where do you goto from there? Just disconnect TPSwitch connector and/or that plus TPSensor connector....or do you go for the throat and disconnect IACV solenoid and see if it still stalls? (probably throws a recoverable fault code and goes for default idle strategy?)...

It's actually one of the worst bits of Nissan nomenclature (also compounded by wiring diagrams when the TCU is incorporated in ECU, or, ECU has a passthru to a standalone TCU).... the gripe ~ they call it the TPS, but with an A/T it's actually a combined unit ...TPS (throttle position switch) + TPS (throttle position sensor).... ..by the looks of it (and considering car is A/T) you have this unit... https://www.amayama.com/en/part/nissan/2262002u11 The connector on the flying lead coming out of the unit, is the TPS (throttle position sensor) ...only the TCU reads this. The connector on the unit body, is the TPS (throttle position switch) ...ECU reads this. It has 3 possible values -- throttle closed (idle control contact), open (both contacts open, ECU controls engine...'run' mode), and WOT (full throttle contact closed, ECU changes mapping). When the throttle is closed (idle control contact), this activates what the patent describes as the 'anti stall system' ~ this has the ECU keep the engine at idling speed, regardless of additional load/variances (alternator load mostly, along with engine temp), and drives the IACV solenoid with PWM signal to adjust the idle air admittance to do this. This is actually a specific ECCS software mode, that only gets utilized when the idle control contact is closed. When you rotate the TPS unit as shown, you're opening the idle control contact, which puts ECCS into 'run' mode (no idle control), which obviously is a non-sequitur without the engine started/running ; if the buzzing is coming from the IACV solenoid, then likely ECCS is freaking out, and trying to raise engine rpm 'any way it can'...so it's likely pulling the valve wide open....this is prolly what's going on there. The signal from the connector on the flying lead coming out of the unit (for the TCU), should be around 0.4volts with the throttle closed (idle position) ~ although this does effect low throttle shift points if set wrong, the primary purpose here is to tell TCU engine is at idle (no throttle demand), and in response lower the A/T line pressure ... this is often described as how much 'creep' you get with shifter in D at idle. The way the TPS unit is setup (physically), ensures the idle control contact closes with a high margin on the TPSensor signal wire, so you can rotate the unit on the adjustment slots, to achieve 0.4v whilst knowing the idle control contact is definitely closed. The IACV solenoid is powered by battery voltage via a fuse, and ground switched (PWM) by the ECU. When I check them, I typically remove the harness plug, feed the solenoid battery voltage and switch it to ground via a 5watt bulb test probe ; thing should click wide open, and idle rpm should increase... ...that said though, if it starts & idles with the TPS unit disconnected, and it still stalls when it gets up to operating temperature, it won't be the IACV because it's unused, which would infer something else is winking out...

Hahaha, yeah.... not what you'd call a tamper-proof design.... but yes, with the truck setup, the lines are always connected, but typically they sit just inside the plane of the rear metal mudguards, so if you clear the guards you clear the lines as well. Not rogue 4WD tracks with tree branches and bushes everywhere, ready to hook-up an air hose. You can do it externally like a mod, but dedicated setups air-pressurize the undriven hubs, and on driven axles you can do the same thing, or pressurize the axles (lots of designs out there for this idea)... https://www.trtaustralia.com.au/traction-air-cti-system/ for example.... ..the trouble I've got here... wrt the bimmer ad... is the last bit...they don't want to show it spinning, do they.... give all the illusion that things are moving...but no...and what the hell tyre profile is that?...25??? ...far kernel, rims would be dead inside 10klms on most roads around here.... 😃

There's actually quite a bit of aftermarket for automatic/manual tyre deflater/inflater systems ... many will have seen YT vids of trucks on tropical forest roads (read: mud), with air lines leading from the chassis/bed down to a hub piece, which in turn connects to the tyre valves ...most of the time only used on the drive axles, to adjust tyre pressures and get some grip....(bit like letting air out of a 4WD to get traction on loose dirt/sand)...

No worries, now that I'm closer to 70yo than not, this sort of stuff will one day be 'lost knowledge'... and even now, I wonder just how many folks out there have the Kent-Moore J34291 shim setting tool set to set end clearances rebuilding these...but right the now, there's less and less hard parts available, and you'll be headed to the wreckers to buy a donor box if it's worn out...(or pay a shop to do exactly the same thing). In a way, it's fortunate the 4-speed was so popular, because there's still heaps of consumables (banners kits, bearings & plates etc) around ~ these early 5-speeds weren't exactly that prevalent, so there's not quite as much about for them... but it's a race between perceived demand for these parts, versus how much they fetch at the shredder for recycling purposes...

'Did' work on them is more accurate ~ on the R31 Skyline forum, you can spot me as 'Solder'... I've written quite a bit about the 4R01 boxes there, and I ended up reverse-engineering the older TCU type operations, so we could fudge a custom TCU to pull off other tricks...and like all things, when you do it a lot, see the failure patterns, have to find parts etc etc, your head ends up filled with whys and wherefores... there was a reason Nissan went with these in more than 60models over 16+ years... all in all, the JR401E based design is an interesting study, as Nissan changed things over the years in a never ending battle against them lunching on themselves <grin>...by the time the RE4R01A rev.C came out (often referred to as RE4R01B), they'd more or less perfected the design...