dbm7

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...

I'll just reiterate that it's best to do all the wiring diagnostics, before even thinking about buying replacement solenoids ~ that is, be absolutely sure the solenoid is bad.....ie; bad connector(s), rodents chewed through a wire, etc etc. If you don't so this, you can fork out all the money for solenoids, only to find something else is wrong (this'll make you cry if you pull the valvebody only to find a broken wire is at fault... ...some more glue on the solenoid packs -- this is the RE5R01A shift solenoid assembly.... ...these are all shift solenoids ~ ostensibly they're the same as the shift solenoids from the 4-speed auto.... ...this is the RE4R01A solenoid set... ...with these, you have 3 shift solenoids attached to the plate, and the separate solenoid is the EPC solenoid (line pressure control) -- with both designs, the TC lockup clutch solenoid (also PWM so they could slide the clutch shut), is located on the lower valvebody half.... ...(story time)...back in the 90's, it was a common fault that the EPC solenoid (or TC-lock solenoid) would fail, but Nissan only sold them as part of the assembly (think ~$350 at the time) ~ thing was, Isuzu also used these boxes in light commercials, and you could buy the PWM solenoid as a separate part, so it was possible to buy/use that solenoid (around $65), and make it fit (remove the circlip, fit to old plate and deal with wiring)...making it a more cost effective repair. I've not seen the RE5R01A shift solenoid assembly, but with the 4-speed RE4R01A it was possible to hack/fit a single shift solenoid onto an other working set, using a donor solenoid from another set with failed EPC....(by rights the whole set should be replaced), but it ends up being a question of how much life is left in the box itself ; sometimes it's a viable repair to fix one solenoid, just to get another 100k of road miles out of it before it needs first overhaul...other times the box is that old/worn, you're as well doing first overhaul and replacing the solenoids and starting fresh... What Nissan did here with the 5-speed, was relocate the EPC solenoid to the lower valvebody (next to the TC lockup solenoid), and stuck the direct-drive clutch solenoid (for the extra gear) where the EPC solenoid used to be on the 4-speed....I can only imagine they did this for serviceability ; the PWM solenoids are most likely to fail, and it's a doddle to drop the pan and change these out (as opposed to dropping the valvebody itself to get at a top mounted EPC)... ...also keep in mind, that some BMW 3/5 series & Mazda (and maybe some Ford/Mazda rebadges, not sure), also used the RE5R01A box under a different name/part number...not saying parts availability is any better, but sometimes it helps to know this when it comes to NOS floating about in the EU.... HTH

That'd be right ~ the early RE5R01A is pretty much the same as the RE4R01A in many ways ; problem is they made lots more 4-speeds than 5-speeds.... I'm in AU, so you'll need apply the US supply scene... https://www.alltranz.com.au/shop/drivetrain/automatic-transmission/Mazda/RE5R01A/#scroll-electrical_components This'll give you the aftermarket parts listings -- you're looking for #56712 & #56713

And the rules change with time ...but speaking to the premise you raise here, some of us old farts will remember seeing every police motorbike with a rubber rear mudflap extension, fitted to the end of the rear mudguard. This was due to an ADR that required the rear mudguard to extend lower than the rear axle (iirc 15 degrees lower as measured at the axle center line)...it was changed in '89 updates, but basically before that date, any road going motorbike was technically 'illegal' (unroadworthy) ...the whole area is a real prickly pear... 😃

M'kay....that's the one (single wire unit is just for dash temp gauge as you say) ; auxiliary air regulator is worth checking, and EFI relay of course.

Check coolant temp sensor ~ symptoms fit the hard hot start/cold start OK scenario --- if sensor goes open circuit, ECU thinks engine is cold and enriches mixture ....works when engine cold, but floods them with rich mixture when hot (Hyundi MAP engines are a bit infamous for this)...

Those 2 solenoids in that assembly I mention, are the PWM solenoids for torque converter lock-up clutch & EPC (line pressure control) ~ when most folks hear of 'solenoid failure', the tendency is to think electrical failure...but fact of the matter is, especially wrt the EPC solenoid (which is moving/running all the time), you can have an electrically 'good' solenoid, that's absolutely broken/worn out mechanically inside...ie; valve plunger return spring rubbing against spring retainer plate, lowering preload pressure.. ...and the solenoid armature extension limit spring wafer with bad wear/broken off petals... ...and if there's ever been any metal flying about, damage to the valve plunger end itself... ...the stuff one never really sees, unless you go the whole 10yards trying to answer the question "why is my line pressure screwy, but TCU isn't flagging any EPC solenoid fault?"...and carefully dissect the solenoid. Worst (and most probable) scenario is when the plate spring petals break off, they get held by the magnetic flux, get mashed up by the armature into little bits, which end up in the space between the armature & shading core bore, and things get stuck or randomly jam up, and your line pressure goes flat and doesn't change...and the TCU never sees it, as it doesn't actively monitor LP... ..then it gets into insidious land, if you end up with lower than expected line pressure...lets say high clutch..and the lower pressure causes it to slip ~ when I say 'slip', think say 2000rpm on the drive plates, and 1800rpm on the driven plates, because the slip is making them under-rotate by 200rpm ; you get all the usual nasties like heat and band/clutch wear, but even if it's only 20rpm slip the same thing happens...and... you'll hardly ever pick this up driving the thing with the torque converter active as it effectively masks these sorts of slippages that are line pressure related ...(the newer TCUs can detect clutch slip rate)...just FYI as it were...

Ahh... it's an early RE5R01A box, that means the pinouts I gave are wrong (they were for the RE4R01A 4-speed box)... I'll have to dig around in my docs to see if I've got that schematic (they used the same gearbox plug, with the vacant pin wired to the direct drive clutch solenoid)...prolly hidden away in a supplement somewhere... ...there were 3 variants of the RE5R01A ~ this early schema was what we called the 'dumb' 5 speed ; it's what jatco called a 'medium duty' box, with torque holding up roughly ~200ft/lbs or so, which was good for NA from RB20/25DE and up to around VG30 output spec. With the RB25DET (and VG33/35 mills), the only options they had was the 4-speed 4AX00 box, which had been beefed up to handle the extra torque (primarily for the VG35, but it also suited the RB25DET mill and others)...and the RE4R03 box in large 4WDs a lot of the time... ...the next variant of 5-speed was redesigned, stronger, and 'smart'...first ones had external TCU with internal (on valvebody) Shift Control Unit, pressure switches, and 2 x TSS...and the last ones had internal TCU+SCU setup, with CANbus control etc etc. @DRoc81 On the RHS of the box towards the rear, there should be a stamped silver ID tag -- what's the model number? Oh...and with the early 5-speeds, the torque converter control solenoid assembly should be replaced as well (31940-60X00)...it's a bit Murphy's Law ....if one has failed, bet on the rest not being far behind ...

...just a note of warning, you shouldn't drive it about with the TCU in limp mode with only 3rd gear available ~ apart from the fact you end up sheering the ATF at the torque converter interface, the high clutch in these isn't especially the strongest, particularly bolted to the RB25DE mill...which is likely a 4AX01 box with lighter duty high clutch (the RB25DET got the bigger high clutch)...be careful out there...

...oops. forgot the TCU end...

...gearbox connector... CD06 -- solenoid A

If shift solenoid A is bad, that explains limp mode --- now you're in the same position as I mentioned previously, in that the next step is to confirm loom/wiring integrity from TCU to gearbox connector with a multimeter (the TCU cannot detect a broken wire, which can happen ..ie; rodent damage, loom rubbed through)...and then finally measure resistance (at the gearbox connector) for shift solenoid A ... ...once you confirm shift solenoid A is bad (open circuit, really low or greater than 40ohm resistance), then it's a job ; you have buy a complete solenoid set, get under the car and drop transmission oil pan, and remove valvebody assembly (the solenoids sit on top), replace solenoid set, and reassemble....it's not exactly a fun task, but readily doable.

Yeah, they're pretty dumb though...ie; they'll throw a solenoid error if the solenoid is dead, shorted, wiring is open circuit, or even if the driver transistor has failed (they can't self-diagnose much, they can only test inputs/outputs)... but if you wanted to try, I believe it's this protocol....(uses a long pulse indicator with short pulse counter)...

Yeah...I always start at the shift solenoids, because there's only a few reasons these will spook into limp mode, and bad shift solenoids is one ~ the other can be the shift control module (if you have steering wheel shift buttons)...it's easier to eliminate the solenoids first.

Aye, it has been pretty good since the shift ~ I just want access to the wiki ..again.. (now the mediawiki stuff has been updated), to get it all straightened out with consistent presentation (I talked to Session about it, turns out the mediawiki version was largely at fault..and pages created with older versions, etc etc)...I've basically given up asking, never get a reply...bit sad...but it is what it is.

From the OP's description, sounds to me like the TCU is in 'limp home' mode --- that is, no actuation power to shift solenoids, and the EPC valve is shut (full line pressure). This effectively sticks the box in 3rd gear, with as much line pressure as possible, to try hold the high clutch clamped shut....and so you get woeful acceleration and don't feel any shifts (because they're not happening). If you don't have Consult or some other scanner to interrogate the TCU itself, you can test with a multimeter to see if it's in limp home mode....ie; stick it in D with engine at idle (hold vehicle with hand/foot brake), and measure the voltage at the TCU feeding shift solenoids A & B -- both should be ON (battery voltage). If they are energized at the TCU, you can unplug the harness from the TCU, and check resistance down through the wiring to the solenoids themselves -- you should see about 20ohms on each coil --- if you do, you can presume the wiring to shift solenoids is OK -- if both measure open circuit, you have to check intermediate connectors in the loom down to the gearbox (and the gearbox connector itself), and check the shift solenoid resistance at the gearbox connector itself --- if the shift solenoids test open circuit here, problem is in the box (ether the solenoids or wiring to them is bad). If you get no voltage at TCU connector for the shift solenoids (and the solenoids/wiring test OK), check powers/grounds to the TCU itself --- if they're ok, it suggests the TCU is the culprit (and you'd need to interrogate it if possible, to find out why it's behaving badly)...

Just FTR, I see this morning the site is up again ~ dunno what was wrong, or if @niZmO_Man worked some magic (thanks if you did)...either way, good to see it back (although by the sounds of it, the future is undefined)...it almost makes me wonder if R31SkylineClub should be incorporated here somehow?... 😃