Lucas 14CUX Firmware / Tune Memory Addresses (Offsets)

The fuel data and software program are stored together with a combined size of only 16KB (16,384 bytes), the data and program together are then duplicated on the tune chip to full 32KB (32,768 bytes).  The 14CUX’s CPU only accesses the second copy at prom file Offsets $4000 to $7FFF, but RoverGauge’s “Save Prom Image” option only saves a single copy to a Prom file with offsets $0000 – $3FFF. As a result I’ve listed both sets of prom offset addresses in the last table. Please note all of the following prom chip offsets / addresses start at the beginning of the prom file at offset $0000 and are not to be confused with the CPU’s internal addressing of C000 - FFFF.  You can use the 14CUX Toolkit to duplicate the RoverGauge single copy ready for flashing to a chip, plus the 14CUXToolkit can fix the checksum if you’ve made your own changes directly in the file.


It’s important to note the location of the fuel data on the prom moved in 1993 for revision R2666 onwards, the old and new file offsets are listed in the first two tables below. In TunerPro you’ll see there are two sets of fuel tables, "R2422" tables for the older prom layout and the other tables are for the later R2666 on layout.  The RoverGauge software is clever enough to automatically identify the correct location of the fuel map to display.


Please note TunePro has now been configured to update the majority of the settings in the tables below except for the Road Speed comparator as its location varies in different tunes and also not for the RPM set points as its not very straightforward to change the RPM brackets.   To run the extended 6203 RPM fuel table please switch to using one of the tunes with the extended RPM table already set-up. If you prefer to create your own RPM brackets then please see the section below on the RPM set points, if you don’t extend the RPM table correctly you could end up with a RPM curve with glitches which then cause a glitches is the ARF as demonstrated in the graphs to the right.


AFR Glitch cause by bad RPM brackets See below




Fuel Map Offsets for Revision R2422 or earlier



Map 1 

Map 2

Map 3

Map 4

Map 5

Fuel Table Start







Multiplier (different CC)







Coolant warn up table














AFM Table Row Scalar







RPM Safety Delta







RPM Safety Limit







Map Last Byte









Fuel Map Offsets for Revision R2666 on



Map 1  

Map 2

Map 3

Map 4

Map 5

Fuel Table Start







Multiplier (different CC)







Coolant warn up table














AFM Table Row Scalar







RPM Safely Delta







RPM Safely Limit







Map Last Byte







Map 1-5 data length = 274bytes/112 hex      (128 FuelTable + 2 Fuel scalar + 144)


Generic Fuel Data Setting


RoverGauge 16KB

Full 32KB Chip File 

Disable application of long term trim 00=Off; 80=On



Overrun fuel cut minimum start $10 (1600rpm), $09 (2,700rpm)

$08 (3,000), $07 (3,400), $06 (4,000rpm), $05 (4,800rpm)



Neutral gear idle increase

$0159 - $015A

$4159 - $415A

A/C idle increase

$015B - $015C

$415B - $415C

Base idle

$0176 - $0177

$4176 - $4177

AFM Row centre offset

$01C7 - $01C8

$41C7 - $41C8

Heated screen idle increase

$01E9 - $01EA

$41E9 - $41EA


$0231 - $023E

$4231 - $423E

Disable Tune resister (north USA) Locked = FF, unlocked 00



MIL On = FF, Off = 00



Start of the program code



RPM Set Points Table

$0800 - $083F

$4800 - $483F

Road Speed Comparator for different sensors   (Offset varies)

$1409 (R3652)

$1323 (R2967)

Engine Tuner/Builder ID if not FF



Revision ID

$3FE9 - $3FEA

$7FE9 - $7FEA

Checksum fixer (See note below)



Tune ID

$3FEC - $3FED

$7FEC - $7FED

Processor's reset vector

$3FFE - $3FFF

$7FFE - $7FFF



AFM Row Table Scalar & AFM Row centre offset

When using a larger AFM you can improve the bottom row usage and move the idle row by adjusting the AFM Table Row Scalar & AFM Row centre offset (in TunerPro see TABLE 1-5 MAF Scalar & TABLE 1-5 MAF Scalar Offset).  The scalar increases/decrease the scale of the rows and the offset move the mid point of the rows up and down.


RPM Set Points Table


RPM set points should be extended to 6250 RPM for TVRs or to the red line of your engine so that you have mixture control past 5500 RPM.


The rpm set points are arranged in 4 columns starting at prom offset $800 with the highest RPM first. The first 2 columns of the table are the 16-bit RPM set points represented as the spark period (2 uSec units) and the 3rd and 4th columns are used to keep the AFR smooth between the set points.


Smooth 6250 RPM Table

04 B0 40 00 - 6250 RPM   Delta

05 94 00 12 - 5250 RPM   1000

06 A8 80 F0 - 4400 RPM    850

07 9C 00 10 - 3850 RPM    550

08 9A 80 F6 - 3405 RPM    445

0A 76 80 7F - 2800 RPM    605

0D F3 80 48 - 2100 RPM    700

10 BD 80 60 - 1750 RPM    350

14 ED 80 3D - 1400 RPM    350

1A A2 80 2C - 1100 RPM    300

20 8D 80 2B -  900 RPM    200

25 8F 80 33 -  780 RPM    120

29 DA 80 3B -  700 RPM     80

2F 40 80 2F -  620 RPM     80

3D 09 80 12 -  480 RPM    140

92 7C 40 2F -  200 RPM    280


If you want to create your own RPM set points do not simply raise the top bracket but spread the difference out over several brackets and the 3rd  and 4th columns will probably require changing along with the 16-bit period value. For further information please see the readme file for the RPM Table Simulation tool that can be used to test different RPM set points.

RPM Table with Glitch that caused ARF Glitch above



Smooth RPM Table to 6250




Checksum Fixer

Every time the ignition is first turned on the ECU program reads though the entire prom chip calculating the checksum to determine if the map is corrupt or been hacked. If the checksum isn’t correct the checksum error code is set which is merely an indication that the prom file has been altered and is not the code of death unless your prom is badly corrupt.  Therefore after updating the prom file with TunerPro the equation below is used to calculate a new checksum fixer to a void the checksum error.  The checksum can also be fixed with the 14CUX Toolkit described on the gadgets page.

          New Checksum Fixer = Old Checksum Fixer - Sum of all bytes in bin file + 1


CO Trim screw adjustment

For non-cat vehicles it very important for smooth running the CO trim voltage is set correct for the different tunes. The CO trim adjustment is via 7/32 Allen key on the side of the AFM and basically the ECU supplies 5v and the variable resister in the AFM pulls the voltage down to ground. Please note RoverGauge only show the live CO trim adjustment once the engine is running or stalled by turning the ignition turning off long enough to allow the engine stop and then quickly back on again.



The column headings for the MAP TEMPERATURE FUEL MULTIPLIER matrix (0x00, 0x36, 0x56, 0x145, 0x171, 0x194, 0x224, 0x238)

on the left refers to hot temp and on the right refer to cold temp.



Coolant Temperature based Idle Control Simulator Program


Land Rover 3.9


Steve Lower Cold Idle





Disable Long Term Trim

If you want to re-map a cat map with without lambda control Mark Blitzracing has proved you can copy map 5 with multiplier to map2 then work on map 2 with the CO trim set to the mid point of 1.25 volts which equals lambda trim 0%.  When finished simply copy the remapped map 2 back to map 5. 


In addition Lucas actually provided a means of turning off long term trim by changing the “Disable application of long term trim” byte.  The value at prom offset $00A0 is normally $80 but changing this to $00 (clearing bit 7) the application of the long term trim is bypassed. The long trim is still calculated and displayed by RoverGauge but is simply not be added to the fuel value. Interesting as the trim is calculated as normal and not applied the ECU keeps adding more and more trim until it hits 100%.  Please note when setting $00A0 to 00 we are current not sure if the short trim is still calculated and applied.


ADCMux & HiRPMAdcMux to remove Road Speed Limiter

AdcMux stands for Analogue to Digital Multiplexer and is a list of sensors that the program uses to control the order the input sensors are read. Each map has its own AdcMux plus their is an additional power up AdcMux list that explains why the CO trim is not read until the engine fires up. While the rpm are above 4185 and the throttle is more than 70% the software uses the special HiRPMAdcMux table in place of the current maps AdcMux table that is heavily loaded with road speed measurements, the 87s. Lucas had a lot of trouble with the road speed limit and the High RPM MuxTable was possibly another patch to try to make the thing work correctly. The actual road speed limiter is in the program code and not the data section. TVR remove the road speed sensor from this list for precats to disable the road speed limiters but on later cars TVR reverted back to the Land Rover HiRPM AdcMux containing the limiter and bypassed the limiter in the program code that works at all RPM. The actually road speed limit is set in the code and it’s location varies between revisions, try look at the value at $2A41 and if it's $C4 then that is the limit in KPH (196 KPH or 122 MPH).

Input Sensor Numbers

87 - Road speed transducer

86 - Air con load input

02 - Air flow sensor (main signal)

03 - Throttle pot

84 - Coolant temp sensor

8D - O2 Reference Voltage

88  - Main relay voltage

8B - Fuel temp sensor

80 - Inertia switch

85 - Auto neutral switch

81 - Heated screen sense

09 - CO Trim screw

8E - Diagnostic plug



AdcMux List

2 (non cat)


5 (cat)






Hi RPM Adc Mux

TVR 1992



8B 86 02 03 84 02 8D 88 02 8B 80 85 81 FA

LR 1991



87 02 87 86 87 02 87 87 87 87 87 87 87 F7

LR 1994



87 02 87 86 87 02 87 87 87 87 87 87 87 F7

TVR 1993on



87 02 87 86 87 02 87 87 87 87 87 87 87 F7



Tunes resistors

Wire Colour







Australian 3.5 & 3.9




Europe & UK 3.9 (or 3.5 Disco)




Europe & UK 4.2 and Gulf States 3.9




Europe & UK 4.2 and Gulf States 3.9




Europe & UK 3.9 (or 3.5 Disco)




Dan's Google Drive

14CUX Wiring Diagram


Demonstrates glitches in the rpm table causes glitches in the ARF


Diagnostic socket plug is a Lucas-Rists 5-way TTS socket housing (female terminals) -


Original Instructions on Piston Heads (August 2013)

Original Overview (November 2013)