TD42 Injectors

The TD42 uses a mechanical indirect injection system, which is fundamentally different from the common rail direct injection found in modern diesels. Fuel is delivered by a mechanically driven injection pump, with individual injectors opening under spring pressure at a set threshold. There is no electronic rail pressure management or ECU-controlled injector timing in the standard TD42 and TD42T. The TD42Ti introduced electronic management into the mix, including a needle lift sensor on the No.1 injector that feeds timing data back to the engine control system. Understanding which variant you have is the starting point for selecting the correct injector.

On a mechanical injection system like the TD42, injector wear tends to show up as black or blue smoke at idle or under load, a rough and uneven idle that wasn't there before, loss of pulling power particularly on hills or when towing, and increased fuel consumption. Hard cold starts are another common indicator.

Fuel leaks from worn or poorly sealed injectors can also allow air into the fuel system, which compounds startup difficulties and contributes to smoke on initial start. Because the TD42's injectors rely on a precise spray pattern to ignite fuel correctly in the pre-combustion chamber, a worn nozzle that dribbles or sprays poorly causes incomplete combustion, which is what produces the smoke and the power loss.

On turbocharged TD42T and TD42Ti setups, properly functioning injectors also play a direct role in keeping exhaust gas temperatures in check. Worn injectors that deliver inconsistent fuel cause the engine to run lean in affected cylinders, which drives EGTs higher and puts additional heat stress on the turbocharger. Left unaddressed, worn injectors can carbon up the pre-combustion chambers and accelerate broader engine wear.

The naturally aspirated TD42 and the turbocharged TD42T use Zexel mechanical injectors that are closely related but calibrated differently to suit their respective fuelling requirements. The TD42Ti added electronic management to the turbo platform, and its No.1 cylinder injector is unique in that it incorporates a needle lift sensor. This sensor monitors injection timing and feeds the data to the ECU for fuel management corrections. The TD42Ti No.1 injector is not interchangeable with standard TD42T units, and fitting the wrong injector to that cylinder will cause timing faults and running issues. Bailey's stocks injectors across all three variants, including the TD42Ti No.1 as a separate item.

Blueprinting is a re-manufacturing process where the injector is disassembled, inspected, and rebuilt to a higher specification than the standard OEM setting. On a TD42, blueprinted injectors are set to deliver a more precise and consistent spray pattern, which improves combustion efficiency, reduces smoke, and in many cases adds a noticeable improvement in throttle response and low-end torque.

For high-performance builds, a conical spray pattern is particularly important for optimal atomisation, and worn injectors that can no longer hold the correct pattern are a risk factor for engine damage in heavily loaded applications. Bailey's also offers a High Flow Stage 1 blueprinted option for TD42 owners running a high-flow 12mm injection pump, which increases fuel delivery to match the pump's higher output.

It's worth noting that high-flow injectors are ineffective without a suitable performance fuel pump to back them up, so for a high-performance build, matched high-flow injectors and a 12mm performance injection pump should be specified together. Blueprinted injectors are particularly popular in lifted or modified Patrols used for touring and off-road work, where a cleaner-running engine under sustained load makes a real difference.

No. Unlike modern common rail diesel systems, the TD42's mechanical injection system does not require ECU coding or electronic calibration after injector replacement. The injectors are set mechanically, and the opening pressure can be tested and adjusted using a pop tester if needed. What is important is that the injectors are fitted correctly with new sealing washers and that the installation is carried out by someone familiar with mechanical injection systems. On the TD42Ti, the needle lift sensor on the No.1 injector needs to be connected correctly and its wiring inspected for condition during the job.

On a high-kilometre engine, replacing the full set is strongly recommended. TD42 injectors are generally recommended for replacement or reconditioning every 100,000 kilometres to maintain engine longevity and reliability.

The TD42's six injectors wear at a broadly similar rate, so when one has reached the point of causing noticeable symptoms, the others are typically not far behind. Replacing a single injector on an otherwise worn set restores combustion in that one cylinder but leaves the remaining five contributing to uneven fuelling, continued smoke, and a rough idle.

When replacing the injectors, it is also worth replacing the injector return line at the same time, as these lines become brittle with age and are prone to cracking when disturbed. Doing the full set in one job eliminates the imbalance issue and avoids the labour cost of going back into the engine within a short period of time.

If you're participating in Bailey's core exchange program, simply send your old injector cores back to us within two weeks of purchase using the prepaid return process outlined on the core return guidelines page, and the deposit will be refunded once the cores are assessed.

Yes, and they should never be reused. The copper sealing washers on the TD42's injectors compress to form a combustion seal at the base of the injector bore. A reused washer that has already been compressed once will not seal correctly the second time around, which can allow combustion gases to track past the injector seat and cause carbon buildup, backpressure issues, and premature injector failure. 

A complete TD42 injector kit includes six injectors and a full set of fitting washers and seals, built to OEM specifications to help restore precise fuel delivery and smooth engine operation in both standard and turbocharged applications.

Always fit new copper washers and inspect the injector bores for carbon deposits before installing new or reconditioned units. Genuine Zexel injectors are manufactured with components including the nozzle, shim, spring, and body, and new units provide better atomisation and sealing than refurbished alternatives. Using genuine components in any reconditioning work similarly enhances the quality and longevity of the finished injector.

Reconditioned TD42 injectors can be a cost-effective alternative to brand new units, and when carried out properly using genuine components, the quality of a reconditioned injector can be very close to new. A well-reconditioned set can resolve common performance issues including rough running, excessive smoke, and increased fuel consumption that has built up over time.

Bailey's re-manufacturing process recovers usable cores and rebuilds them to a consistent standard, giving TD42 owners a practical option for restoring fuel system performance without the cost of a full new set. The price difference between reconditioned and new units makes reconditioning a worthwhile consideration for standard applications where OEM output is the goal rather than increased performance. 

That said, where budget allows, new genuine Zexel injectors remain the preferred choice for the best atomisation and long-term sealing performance.

Yes. If you're unsure whether your Patrol is a TD42, TD42T, or TD42Ti, or if you're running pump or engine modifications and want to know which injector spec suits your setup best, the Bailey's team can help. Bring your build details, engine number, or any pump modifications you're running and we'll point you toward the correct unit before you add anything to your cart. Thanks to decades of hands-on experience with the TD42 engine family, our team can navigate the differences between variants quickly and get you sorted without back-and-forth guesswork.