EFI  A "basic" guide in layman's terms.
by George Dow
EPROM is the plug in chip that all to many think they can fiddle with to get "more" performance, the letters stand for... Erasable Programmable Read Only Memory.

The EFI , (Electronic Fuel Injection)  ECU (Electronic Control Unit) is made up of components kinda like your computer, only smaller. It processes information in a similar way in that it has inputs and outputs and the PROGRAMMING determines output relative to input. In other words, your computer has peripherals.... Printer, scanner, mouse, keyboard,monitor etc.etc. the automobile ECU has sensors, flow meters, injectors etc. etc.

Just like early computers the early EFI kit is less sophisticated and has fewer functions, Now however there are a myriad of digitally processed functions available to auto engineering that make old EFI seem simple.

So the ECU is a "processor" of information and dependant on the information it receives from the sensors (input peripherals)  its PROGRAMMING will determine what signals it sends to its actuators (output peripherals). or injectors etc. if you prefer...

The programming is all important here, just like the many differing programmes on the market for printing, scanning or photo applications, etc. all of which should operate on your PC, though perhaps with different aspects to some functions, some more suitable than others for your requirements?  So Programming is ALL when it comes to EFI. (unless the
peripherals have a fault)

The hard disc on your computer along with its BIOS (Basic Input Output System) Chip, RAM (Random Access Memory)Chip, ROM, (Read Only Memory) all fits into a system of hardware that enables processing of information. there are many other components, though I do not wish to cloud the issue (-:

The EPROM is the device in an ECU that holds the PROGRAMMING, it acts asl the memory device that your PC needs to cope with its tasks.  As EPROM is Erasable Programmable Read Only Memory, it is similar to a floppy disk or CD  in your PC and it`s physical form is a multipin chip which can be plugged and unplugged at your ECU by various interface devices (sockets). The EPROM holds the programming and with the correct interface it can be plugged into a PC and if the PC has the correct software, the programming on the EPROM can be studied or downloaded into the PC and copied and modified. It can even be sent by modem to a garage miles away for the mechanic to load into a waiting EPROM plugged up to his PC.

For you guys who are "really" paying attention......if its Erasable and Programmable,  how come it is read-only ???  Well obviously it can be written to..... Though only when plugged up to a PC that has the software to write to it, So when it is in place in the ECU the programming is "read only"....... In order that it is "safe" from corruption (Changes to any aspect of the programme)

So we have:

Input.....Programming......Output   Roughly in that order, and it can be seen that modification of the programme will affect the output. The programme like most is made up of stages and what happens at any stage can be programmed differently to suit requirements.  For example, if we want maximum acceleration, the w want loads more throttle and fuel though in a measured way that provides the ideal mixture for max acceleration. (This may be ideal in a racing car, though not likely to impress the guys
who measure emissions.) So we have sensors in the CATS (catylitic converters) to say ...."Hold up on the fuelling..... the mixture is too rich for those governement guys!!

Modern cars, their sensors and programming are configured in such a way as to appease many demons, this leaves an opening for those with the necessary software to alter the EPROM programme and thus fuelling by tweaking the amount of fuel air mix and timing to give "more" in certain circumstances.Though many would be chip programmers are not much more than computer literate chancers!! BEWARE!!

The optimum settings SHOULD have been programmed in at the factory and in general terms I suspect they are a best average for average conditions and an average driver....... I guess if there is one word that is difficult to apply to a Morganeer or his car.....It has to be .."average" !!  Though I suspect the EPROM on your ECU is programmed for a huge lump of a Range Rover,  and therefore the average settings leave room for improvement for a suoper light sports car.  As far as I am aware MMC do not modify the original RR programme. Therefore there is possibly room for improvement.  I`m aware of modern systems that have an inbuilt ability to "learn" from your driving style and thus modify the programming within the confines of current emission regs...... Orwellian or what !!!!

But for a DIY are more of a good fit. I like the early systems designed with  no exhaust emission sensors as an input.... Kinda "relatively"... raw unsophisticated power..... Just the way I like it!

I hope someone somewhere has found this ramble in some way  useful.

Cheers,   George.