first time swapping rb25det into r34

[dingleberry]

hows it fellas,

my first post here which seems crazy cos half the forums i read are like the same age as me haha.

to make a long story short ive got an r34 sedan (rb25de neo auto) which im swapping to a s0/s1? rb25det, r33 big box and nismo gt pro lsd.

i have the motor and gearbox all bolted up outside the car, old motor and trans out.

i bought the motor with stock ecu and loom, do i switch over to that? or will it be easier to get a r34 manual ecu and keep the loom if thats even possible. 

also engine mounts look different, anything else thats different or incompatible?

cheers, hope this all makes sense

Paddy

[Duncan]

This seems to be a very popular swap since all the turbo skyline prices went through the roof!

I'll let someone more familiar chime in, but I understand that yes you probably want to swap the loom in to swap out the auto TCM stuff. You should not assume everything just plugs in either, you need to check at least the ECU wiring diagram for any differences at the plug at the left headlight and probably the ones near the ECU that join the dash loom too

 

[GTSBoy]

Let me assume that the concern over a manual ECU is that the NeoDET that you have was an auto and has an auto ECU. That ECU will not be a problem, but you WILL have to Nistune it. And you would have to Nistune it even if you had a manual ECU, because the turbo ECUs will shit the bed if they do not have all the things that they were told they have to have, to be happy. The big one being the TCS CU, which you won't have in your car.

Anyway, with an auto ECU (which I have running my originally auto NeoDET in a manual R32) Nistune allows you to put in a Stagea image which doesn't panic about the absent TCS, and allows you to override a whole bunch of other annoyances that would otherwise see the check engine light on 100% of the time. Also, you can't wind up the power very far on the stock NeoDET ECUs without Nistune, because the boost sensor gets in the way. Nistune allows you to push that problem much further up the dial. Do you even have the boost sensor with the engine? Without it, you are SOL and will need an aftermarket ECU (or to find a sensor somewhere, god knows where).

I can't tell you what the wiring loom differences are in a 34. But what Duncan said above needs to be considered. When you say "loom", does that include the transmission loom? Because you will need to swap out the auto tranny loom for the equivalent manual loom, and get rid of the neutral/park start interlock (basically hot wire it).

[Kinkstaah]

I do believe from context he is talking about a S0/S1 R33 RB25 with associated ECU and Wiring for that, and a manual gearbox into a R34 N/A Auto.

I don't have the knowledge of all the pinouts and such but my gut feeling from doing my own conversion is to use as much of the R33 stuff that you can. The "car" wiring is quite seperate from the "Engine" wiring when all things are considered.

The only things to truly consider 99% of the time is the cluster, reverse lights and potentially disabling the 'not in P/N' immobilizer circuit.

[Murray_Calavera]

This sounds like a perfect excuse to install a Haltech R3.

[MBS206]

42 minutes ago, Murray_Calavera said:

This sounds like a perfect excuse to install a Haltech R3.

Came here to say, put all the wiring from the new motor and gearbox in that you can, then throw the stock ECUs in the bin, and get an aftermarket ECU. Should be pretty easy if you can use a multimeter and read a wiring diagram to then use a PNP aftermarket ECU to suit the motors wiring loom, and make the minimal changes you will to get it to work in with the body loom (If any).
This will mean you can very easily circumvent/bypass the Park/Neutral start disable switch, and get everything running really easy!

[WMDC35]

I've done this both ways, I'd use the original loom & swap plugs on the engine side as you'll usually end up changing a lot of those anyway.

Series 1 is usually non ABS which requires wiring which I can't remember how to do as haven't done it for over 15 years.

The auto inhibitor is easy to bypass or in the meantime you can put it in neutral & unbolt it & tape it somewhere in the bay haha, then just wire reverse lights.

I'd go straight to aftermarket ecu.

A few basics are built in ignitor coils & reverse the CAS wiring, sort the plugs for whatever injectors & IAC-you can use an adaptor for the neo type otherwise the s1 will still work, use the knock sensors that suit the loom & it'll be pretty much running.

 

[dingleberry]

thanks very much for all the replies, huge help.

to follow up with @WMDC35 so stick with the de neo loom? would some sort of plug and play ECU designed for the r34/25neo work? looking at maxxecu’s but open to suggestion 

[WMDC35]

On 22/06/2025 at 9:05 PM, dingleberry said:

thanks very much for all the replies, huge help.

to follow up with @WMDC35 so stick with the de neo loom? would some sort of plug and play ECU designed for the r34/25neo work? looking at maxxecu’s but open to suggestion 

That's how I'd do it, I haven't used Maxxecu but most ecu's that work with rb25det neo will work with the neo de loom etc, check with whoever is going to tune it if they have a preference, Link is good in NZ as most tuners are fine with them.