Although Chevy 350 V8 and Chevy LS V8 conversions into 4wd vehicles are the most common in the US, based on their affordability, availability, price and number of people that know how to work on these engines, the Lexus 1UZ-FE V8 engine from the Lexus LS400 and other models, has now become a popular alternative for Lexus and Toyota enthusiasts, that want to stick with the same brand as the vehicles, but want more power in their 4wd. The 1UZ-FE 4wd conversion is also already extremely popular in many other countries and has been for many years.
On main problem encountered with this conversion, is when using the automatic transmission that comes with many of them, and trying to adapt it to word with the 4×4 transfer case in the 4wd that it must be put in. That will basically determine which ECU or engine management system will be used, and what level of computer programming or wiring will then be needed to be performed.
These are actually very tough, basic and reliable engines, and provide great power for the money, and the low weight they offer. The main reliability issues that is usually read about on forums or social media, comes from the poor quality work that went into the conversions in the first place from many backyard mechanics. When done right, this engine will outlast most factory OEM engines in any rough off road situation, and take all the abuse you can throw at it.
When wanting to use the standard 5 speed automatic transmission that these donor engines come with, in a 4×4 vehicle, you need to ensure a few extra things are done in the process, to make it work correctly firstly, and suitable to the 4wd application.
Engine Management System
If you plan to use this engine with the factory 5 speed automatic transmission that they are often sold with, you should not be installing it with the factory engine management system, as this management system was design and programmed for use with a normal road car like the LS400. So, it will shift at the wrong rev ranges for 4wd use. Another big problem, is for instance when you are driving down a steep slippery descent on a trail, like a wet or muddy hill, or a sand dune, in those situations, as most experienced offroaders know, you should not be using your brakes to slow the vehicle down, as that would cause it to lose forward traction, causing it to often start sliding sideways, which could easily cause it to end up rolling over and all the way down the hill or dune.
With a manual transmission, the best method would be to put the transfer case in low range with the transmission in first gear, take your feet off the gas and brake pedals, and just steer whilst letting your engine do the braking braking against the low gearing so you maintain forward motion and traction with the wheels, and still maintain steering and control of the vehicle during the descent.
With modern 4wd vehicles with automatic transmissions, those engine control units are programmed to keep the transmission in a low gear during descents, so it also provides engine braking against low gearing, to serve the same purpose.
These engine management system that Lexus has in these 1UZ-FE engines with the 5 speed automatic transmissions, was not programmed for slow off road descents, as they were installed in road cars, so when using the factory management system, it becomes very dangerous in such situations off road, and that is one of the main reasons why we would definitely recommend having a good aftermarket engine management system installed with this engine in your 4wd, by a reputable shop that knows how to program it for off road and 4wd use.
Most 4wd vehicles also have completely incorrect diff ratios for the gearing in this 5 speed automatic transmission, so you should definitely change your gearing in your differentials to suite this transmission gearing with the tire size you plan on running with it. The diff ratios often make or break the 1UZ-FE 4wd conversion.
Transmission to Transfer Adapter
In order to turn the factory 5 speed automatic transmission that is usually sold with these engines into a 4wd transmission, which you would want to do to make a 1UZ-FE 4wd conversion, it needs to be mated to the transfer case of the vehicle you are putting it in, or else have a custom transfer case made for it. The first option being the easiest and cheapest, also the most straight forward regarding interior and knobs if the vehicle you are putting it in was a factory 4wd.
It is important to prepare the 1UZ-FE engine you buy well before you drop it into your vehicle, basics like giving a normal service of all oils, belts, plugs and filters if you know the condition and mileage of it, but I would also highly recommend opening it up and checking the condition of the valves, sleeves, pistons and cam if you do not know the condition and mileage of it. This will give you piece of mind and prevent having to pull it again in future for costly repairs soon after putting it in.
The other major issues that needs attention before hand, is ensuring the radiator, fan and cooling system that you are putting into the vehicle with it, is firstly sufficient enough to keep it cool under all load circumstances, and fit into the engine bay with it.
You have to be sure to check the clearance of the steering shaft, as well as the sump or oil pan to make sure that it does not come into contact with the front axle even on full articulation or compression, and that the engine always gets oil, even at strange angles that your 4wd may find itself in.
Lastly, depending on whether the 4wd vehicle it is going in is a closed vehicle that you will be using daily on the roads or not, often the most costly and difficult part of the whole conversion, that a lost of people forget about until the end, is the air-conditioning system, and adapting one to work with this engine, inside the vehicle it is going in.