Diesel tuning and remapping your four-wheel drive – why you shouldn’t be afraid of a safe tune

By Sam Young 15 Min Read

There’s no denying, that performance tuning your 4×4 is one of the most rewarding upgrades you can make to how your vehicle performs on and off-road. Not only can you increase the horsepower and torque figures. But often you can improve fuel economy and even help increase the longevity of your vehicle. 


For a long time, the concept of tuning a vehicle was a little scary. There was a lot of misinformation out on the internet and a stack of horror stories. But as technology has improved, it’s now one of the safest and best bang for buck-changes you can make… if you do things right.  

Whilst I’m sure there are more qualified gurus out there, I’m going to try and tackle this in layman’s terms. So strap yourselves in. I’ve consulted Hayden from HD Automotive, and I’ve got the information we need. We’ve broken this down into a few key points so you can follow along at home. Let’s dive in!

What exactly is a remap?

In the context of diesel 4×4 tuning, a “map” refers to a set of parameters that are programmed into your four-wheel drive’s computer to control various things such as fuel injection timing, injection duration, and turbo boost pressure. 

These maps are pre-loaded by the manufacturer to give a balance between performance, fuel economy, and emissions. That being said, tuning shops like HD Automotive have the ability to reprogram or ‘remap’ the computer to give more power and torque, increase fuel economy, and a host of other things. 


Boost doesn’t equal power

We asked Hayden what one of the biggest misconceptions was when it came to diesel tuning. Here’s what he had to say; “One of the first topics of any conversation around the performance of a vehicle is ‘So how much boost does it run?’. When it comes to tuning diesels, boost does NOT equal horsepower. Boost acts purely as a compensating method to the fuel provided to the engine.” 

If you’re not quite following, don’t worry, you’re not alone. Hayden had a great example for us to help understand. 

“Say you’ve got a factory Non-Turbo TD42 Patrol that has had a turbocharger kit fitted to it. When fitting the kit, you also fitted a boost controller and want to turn it up because more boost means more power, right? So, you turn the boost controller all the way up, hook your gauge up and go for a drive and with great success, you’re running 20psi of boost pressure!” 

What went wrong?

Sadly, it’s not that simple! Hayden continues with; “there’s only one issue, the vehicles barely any quicker. What’s happened here? Let’s say that the TD42 Patrol on the stock 10mm fuel injection pump produces 90HP at the wheels at an air-fuel ratio (AFR) of 22:1, this AFR may already represent the maximum amount of horsepower at the desired mixture of fuel and air in the cylinders. All we’ve done is add substantially more air into the equation. Luckily for you, this is not dangerous on a diesel as it does not ‘detonate’ like a petrol engine and suffers from leaning the AFR out. All it does is restrict the engine, and throws that AFR up into the 26:1 + zone. Which will produce less power than its previous optimum mixture of 22:1.” 

Now whilst this might seem like a tricky equation to try and get right, at that stage, you would need to add more fuel to make up for the amount of air! I guess what we’re trying to get at here is, don’t get too caught up on ‘boost’ numbers when it really comes down to each individual vehicle. Speak to your tuner, get the right advice, and see a professional.


Modifications needed for tuning

One of the most common reasons people decide to tune their car is to help give them that little bit more go, generally down low and in the mid-range of the revs. One of the questions Hayden at HD Automotive get’s asked day in, day out, is, “Do I need other modifications before getting my 4×4 tuned?” The simple answer is no. Let me explain. 

When it comes to ECU remapping, you can do it to your vehicle at any stage in the build process. A lot of people think it’s not worth doing until you have all the other bells and whistles fitted to your vehicle, but it’s simply not essential. 

For many, remapping is still the best value. Whilst fitting things like snorkels, airboxes, exhausts and other bits and pieces, they’re simply not needed before getting an ECU remap. In fact, if your budget is only going to allow one or the other, you’d be crazy not to opt for the remap first. 

A simple remap on your 4×4 can lead to incredible performance gains. It does depend on the vehicle, but it’s not uncommon to see 20%, 30% or even 40% gains. Whilst having the other accessories may help you extract a tiny bit more from the vehicle, the core of the work is done in the remapping process, and that money is better spent elsewhere! 

The other wonderful thing about an ecu remap is they’re often undetectable to a manufacturer which means if you do need to go back with a warranty related issue and the vehicle is otherwise stock, you shouldn’t have a drama! 

Common dyno issues

Dyno tuning and remapping a vehicle can seem a little scary. You’re running up your pride and joy on a dyno to it’s absolute maximum potential. Cycling through the gears, revving the vehicle all the way to it’s redline, it can be really stressful! It’s important to remember that a dyno puts no more stress on your vehicle than what driving it aggressively on the road would, so try not to worry! Also, as long as you have a professional operating the dyno, and everything is set up correctly, you’re in the best possible hands to keep your ride safe. 

That being said, there are a few common issues that tuning shops like HD Automotive see, so we thought we’d run you through them so there’s nothing to surprise you. 

Intercooler piping

One of the common issues tuning shops see is blowing intercooler piping, leaking radiator hoses and other annoying little niggles like that. If you’ve just been recently working on the car yourself or done some DIY upgrades, make sure you double check your work the night before the tune! Sometimes a loose hose clamp can cause absolute havoc to your tuners day, and trust me when I say, making sure it’s tight before the dyno instead of cleaning up 10L of coolant off the dyno floor is definitely preferable for everyone. 

Another simple issue that people somehow forget is fuel. Make sure you have a full tank in the vehicle when you drop it off! Whilst this seems trivial, you’d be amazed at how many times customers at HD Automotive have dropped off a car basically on the fuel light. Whilst an ECU remap is usually pretty quick and straightforward, and running it up on the dyno doesn’t take much, from time to time, a car may need to sit idle or be run up on the dyno a handful of times. Running out of fuel is one thing that a tuner is not going to take kindly to. 

The other issue, or I guess a piece of advice Hayden and the team speak about is communication. It’s up to you to tell your tuner exactly what you want out of the tune. If you’re chasing the most power possible, then let them know. If you’re chasing a conservative and fuel-efficient towing tune, then let them know. The worst thing possible is not communicating what your expectations are and then being unhappy with the result. 

Proper service including filters

Before having your 4×4 tuned, you really should have it inspected and recently serviced by a qualified mechanic. Before you start spinning the rollers. Simple things like fresh oil, and fuel will give your engine it’s best chance. As will having fresh filters, mainly the air filter and fuel filter, so there are less restrictions when it comes to the things engines love. Fuel and oxygen. A good 4×4 service kit will include these items, they aren’t expensive, and any one can change their air filter, for example, at home. Dyno time, on the other hand, is not cheap and requires a specialised operator. Don’t waste their time, and your money, by rocking up with a vehicle that isn’t in the best shape it could be.

Catch cans

It’s a wise move to fit a catch can, if tuning your turbo-diesel engine. These motors are going to be working harder, as they are producing more power, thus breathing heavier. So, it just makes sense in our eyes to install a good catch can. If you would like to know about how catch cans work, we’ve written a separate article here. The key, is fitting a good quality catch can, from a reputable manufacturer. And to service it at the recommended schedules.


A car with good power and awful suspension is one of the worst things to drive. I wish more people thought about supplementary modifications like suspension upgrades, to get the most out of these new found performance gains. We always say, a properly tuned, quality suspension kit, from someone that specialises in 4×4 suspension, is something you’ll enjoy every time you turn the key. More power, means you’ll use that extra power. Budget in at least having the suspension inspected on your vehicle as a minimum. Which leads us to…


Brake upgrades are another important aspect to consider when extracting more power out of your 4×4. There are so many options on the market these days, it’s really a no-brainer. This is especially true, if you are going to be using this new found power for towing. Brake upgrades can range from a simple pad, and disc upgrade, and perhaps some braided brake lines. Then there are big brake upgrades that could include brake booster, caliper and rotor upgrades.

If in doubt, consult a brake and clutch expert, or suspension expert who can test your brakes for you, to see if they are going to be up to the job. If not, you’ll need to look into a quality brake upgrade. This is serious stuff best left to the experts.

Clutch upgrades for manual transmission

If you own a 4×4, with a manual transmission, you’ll probably have to upgrade the clutch if chasing more power. This is quite common with V8 powered 70 Series LandCruisers, and the KUN (or N70 as some call it) HiLux. Toyota aren’t alone here, most OE spec clutches don’t seem to handle more power for long. It’s just more people are tuning the LandCruiser and HiLux. And they get good results. That is, after the owners fit a heavy duty clutch kit, that will handle the extra power, while not being a chore to operate on-and-off-road.

Last piece of advice

Tuners are very talented people and can accommodate what you’re after 90% of the time, so as long as you speak up, you’re good to go! 

Tuning your diesel 4×4 is a very rewarding thing to do, and something that I recommend to anyone who will listen. It’s important to understand the process thoroughly and put your faith in a professional, and believe me when I say, you won’t be disappointed with the outcome if the job is done right the first time around. Get it wrong, and you’ll know about it.

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