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1,414 Posts
Discussion Starter #1
Hello does anyone know if the motor ecu harness ect from a 96 5 speed t100 will work for a 3.4 swap in to a 94 pickup.Thanks in advance ! :cool:

13,296 Posts
Go over to YotaTech if you don't get the answer here... (Hoping thefatkid chimes in here though)

1,110 Posts
i think that as long as you get the motor,harness and ecu from the same vehicle it should work.

1,414 Posts
Discussion Starter #7
Hey thanks guys this helps me out! Also to thefatkid do u have any experinece with doing the wiring on a 3.4 swap?

1,414 Posts
Discussion Starter #9
Oh really!! I'm getting to know people still!! lol!! good cuz I'm going to need help on the wiring!!

1,414 Posts
Discussion Starter #10
I hope I can pick his brain!!;)

1,110 Posts
I hope I can pick his brain!!;)
He is a nice guy and will help you out. there is also a lot of information on it out there if you search. here is some that I have on it.
(sorry its a long post)

Could there truly be so few wires???


All right, the wiring.

Of course, all swaps will be a little different... but this is my swap, so take what you
can from it and run.

Basically, the 3.4 ECM and the 3.4 motor work as a team. They don't care in what vehicle
they are mounted. Just give them air, fuel, coolant... and you'll have a very happy

Then your vehicle needs to be told some information so you can see what's going on
through your various gauges. Of course, that step could even be skipped. The 3.4 doesn't
care if you know what's going on after all.

One thing the ECM also needs is power. That is provided from the original 3.0 body
harness. How it gets this power is important, as other related '90 components need to be
told what to do as well

These are the wires I hooked up:

IG2 from the '90 to the IG2 circuit wires from the 3.4 harness.
Engine coolant sensor from the 3.4 harness to the '90 wire from the temp gauge.
Oil pressure sender from the 3.4 harness to the '90 wire for the pressure gauge. (note,
'90 pressure sender is used on the 3.4)
Indicator lamp pin from 3.4 ECM connected to the '90 gauge indicator lamp wire.
Stop light switch from the '90 to the 3.4 ECM stop light pin.
Speed sensor from the '90 gauge to the 3.4 ECM.
3.4 ECM circuit start relay pin to the circuit start relay on the '90.
3.4 EFI relay pin to the EFI relay on the '90.

And that's almost it.

I ran a new wire from the STA pin on the 3.4 ECM to the starter itself. That particular
wire got lost in the '90 harness for me.

I haven't done the AC yet, but have pulled the wires from the AC amplifier and related
from the '90 as well as the 3.4 ECM so I can connect them when I figure that out.

I still need to do the 10ohm tach mod so the '90 tach can handle the 3.4 signal, but that
wire is marked from the 3.4 ignitor and just needs to be connected.

There is one pin from the 3.4 ECM that is for the OBDII port. 4 wires in total need to go
to the port. Second is a ground from the DS intake, third is a standard body ground and
the last is a 12v power supply with a 7.5a fuse. I still need the port, but have all the
wires to plug into it when I get one. And as I have learned, any vehicle post '96 will
have one that I can use.

I left the 4WD, cruise control and ADD pins disconnected from the 3.4 ECM as I did not
need them.

You'll probably find as I did that many of the systems between the 3.4 equipped vehicles
and the 3.0 equipped vehicles are very similiar. Of course, the newer the 3.4 you get the
farther the two systems will be apart. If you have the Toyota factory EWD from both your
donor vehicle and current vehicle most of the pieces are fairly easy to figure out.
Patience and accuracy is the key.

You may also find that 95% of the 3.4 ECM to the '90 connections are located in one plug,
plug D. Also, 95% of the connections you'll need from the '90 are right there in the PS
kick panel by the original ECM. Plug IH1 and IH2 had almost all I needed to connect to.

If I did a swap again and found a donor with a uncut harness I'd have been miles ahead.
Adding a supercharger or an automatic into the equation would surely complicate things,
but I'd imagine still something that could be handled.

Mind you, I am just fine sticking with the complexity of the 5spd swap... that was hard


13,296 Posts
I hope I can pick his brain!!;)
We pick Brian (thefatkid's) brain a lot, but remember this is his business so if you need more than some answers to a few questions you might want to throw some money (or whatever he wants... Beer??) his way. We always try and treat thefatkid well, he is a life-saver I tell ya!

13,296 Posts
Also MrDoug put together a fantastic TO do list (in order) - he's anal that way. I'm re-posting it here.

Mr Doug's list:

This is my list of what needs to be attacked and in roughly what order. Some things can be done out of order, others cant. I think it's obvious, but I'm constantly going thru the list and making small changes based on whatever I'm thinking at the moment (go figure why the saved file had some non-sense in it.)

front clip
body mounts
remove fule/brake hardlines
paint engine bay

fan shroud

re-gear t-case
dual adapter

pull engine
check/replace timing belt
check/replace water pump
replace oil pan and pickup
drill oil dipstick
spark plugs/wires
build crossover pipe

buld crossover pipe
place engine with bell housing, tranny, dual case and case mount
cut up tunnel
weld motor mounts
weld t-case mounts
rebuild tunnel

pull bed
move rear crossmember
gas tank mount

pull cab
paint frame
mount bed

paint inside cab
paint under side cab
mount cab

hookup body electrical
install dash

mount engine
install flywheel
install clutch, throwout bearing, pressure plate
mount tranny/t-case

modify hood

Mount airbox
Heater hoses
radiator hoses
speedo cable
throttle cable

fuel lines
evap vsv's

clutch master
clutch hydro
clutch slave

Battery tray
engine electrical
fan temp sensor/switch

o2 sensors

brake master
v6 calipers
brake hydro
underbody heat shields

front springs
shock towers

P/S gear
P/S cooler

rebuild front hubs


rear shackles
replace rear axle
rear spring perchs


front bumper
wire winch


Oh, and here's my parts list for what I need to pull/gather for the 3.4 swap part of my build:

Motor Purchase:
Exhaust Manifolds and crossover pipe
Intake Plenum
throtle body
injectors, fuel rail, VSV's, Sensors
Alt + brackets
P/S pump + brackets
coil packs
engine harness
oil pressure sending unit

Other Source:
Cat (1 or 2 depending on motor)
intake airbox, tubing, MAF
air flow meter
evap canister
evap vappor pressure sensor
evap pressure VSV
evap purge VSV
5vz fly wheel, pressure plate,
3vz throw out bearing, clutch
o2 sensor exhaust port (2? check exhaust mani bung)
3vz radiator, shroud (90-95 v6)
clutch slave cylnder
clutch master cylnder
2wd T100 oil pan, oil sump, dipstick
throttle cable

Maint Items:
o2 sensors (2)
spark plugs and wires
5vz clutch

7,735 Posts
My to-do list is for my full build (replacing almost everything). It wouldn't apply to a simple 3.0-3.4 swap.

I'll throw another vote for theFatKid. If I remember right, he specializes in electrical trouble shooting and I plan on throwing some money his way to help me with the wiring harness.
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