Jaguar XJ (X350) 2003-2009 4.2 V8 400bhp remap figures

Who is the Stage 1 map for?

• Drivers who want a sharper throttle and a small, honest gain from software alone.
• Owners who would rather keep the car standard in every other way.
• Anyone who wants the fullest software-only map for this engine, accepting that the gain is modest without a turbocharger.

What this means for your XJ

Without a turbocharger the improvement comes from ignition, fuelling and throttle mapping rather than boost, so expect a smaller but still noticeable change in response.

The ECU recorded for this variant is a Denso. Older engine management is simpler to work with, but age matters: worn sensors, leaks and tired components can hold back what a remap delivers, which is why we run a diagnostic check first.

We remap at our Belgrave Gate workshop in Leicester, or at your home or work within 30 miles, and every job starts with a diagnostic check.

Please note: these are expected figures, not guarantees. Real results vary with the condition of the vehicle, the ECU software version, fuel quality and the hardware fitted. Some options - including Stage 2 and anything that needs extra hardware - are for off-road or competition use only. We check every vehicle first and confirm what is achievable before any work starts.

Figures reviewed 22 October 2026.