ECU _ Basic details of Lotus Esprit S4

1. Basic ECU Details

The Lotus Esprit 4-cylinder cars from 1989 onwards were equipped with a GM/Delco ECU (also found in the Vauxhall, Opel or even Holden). The GM Part No is 01228708 they can be sourced from a number of GM/Delco parts specialists in the US such as AUTOECM. However the Memcal is unique to the Esprit. The only source of Esprit memcals I am aware off is from John Welch at WC Engineering. You can often pick up Esprit ECU's for about £100 from parts fairs but they will never contain memcals at that price.



2. Memcal

The Memcal is a large brown and blue 'T' shaped plastic carrier that plugs into a special 50 pin socket inside the ECU. Half of the MEMCAL is an 27C256 EPROM [128Kbits - 16K bytes, 150ns or better] that contains the computer software and look-up tables for a specific vehicle. The other half of the MEMCAL is that neat little board covered in "squishy clear jelly" and a couple of chips beneath it. The circuitry covered in the clear jelly is the Electronic Spark Control [ESC] module The ESC module is engine specific (2.2L 910 and 2.0L 920 engines have different ESC modules) it is basically an acoustic filter circuit that listens to the output from the knock sensor and sends a yes/no signal to the ECM to indicate the presence of knock. As you can imagine, an incorrect PROM can cause a car to run bad, or not at all. An incorrect ESC module can tell the ECU that knock is there when it in fact isn't, or worse yet, NOT tell the ECU when knock is present. The two chips under the SC board are the chips that powers the car in "limp home mode" in the event that the EPROM fails.

Sanjaya Vatuk provides a memcal reprogramming facility for US Esprit owners.

3. Chip Tuning

Over the past 5-6 years several people such as John Welch, Andy Whittaker and most recently Marcus Freudhoefer (PUK) have reverse engineered the engine mapping stored as a binary file in the EPROM, on the ECU's memcal. Once that had been achieved they are able to produce new chip variants that can either improve the overall running characteristics of the engine or increase boost and so up the cars performance.

PUK now sell are large number of chip variants for the SE, S4, S4s, and GT3. They have been extensively reviewed by LEW.

Summary of Most Important Modifications

Cooling Fans On:
Cooling Fans Off:
High Boost fuel Cut-Out pressure
1.25 bar
1.24 bar
Engine overheat temp:
   for more safety
Engine overheat reset temp:
   for more safety
ECU Boost Control threshold temp min.:
eliminates the low-boost-thermostat-problem
ECU Boost Control threshold temp max.:
   for more safety
Overboost RPM trigger:
for more low down torque
5000 rpm
RPM+TPS overboost wastegate add-on:
(only comes on when RPM>3500 AND TPS>94%)
2.3 %
Off course the other tables: ignition, spark, fuel, idle, boost controller,... and correction tables are also different.

I am currently running the Chip #6 supplied by PUK. It contains the following modifications to the latest evolution for the S4s code.

4cyl. Chip #6. Red-Race-code

— special code based on the S4s-Mk5 or Sport300
— max. boost up to 1.25 bar
— Codes personalised for your Esprit


click to enlarge




One of the best step by step guides for modifying the memcal can be found here .



4. Further Reading

Freescan Page

ECU Tables Page



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