4-cylinder GM - AC Delco MPFI

What is a Mem-Cal?

The Mem-Cal (Memory-Calibration Pak) contains data tables that determine what the default operating parameters are for the system. These values are used during initial boot-up of the ECM, or after re-application of power any time the ECM power has been disconnected for over 30 seconds.

Each vehicle usually gets a specific Mem-Cal designed for it. This is why you need a different Tech-1 cartridge for different vehicle and/or model year.

So, although the ECM can be the same for various engine applications, there's no reason why each Mem-Cal can't be designed/programmed unique enough so that the defaults give adequate performance for each type of vehicle.

Someone asked the members of the Lotus List if his "thumpy idle" could be adjusted by somehow altering the ECM data. Seeing as I'm referred to as a sort of resident expert ;-)of ECM-related issues, I figured I had to toss in my 2 pennies worth.

If you hook up a Tech-1 scanner tool with a proper Lotus cartridge to either diagnostic port of the ECM you will find that there is a parameter called "Desired Idle". According to the Lotus Service Notes this indicates the rpm to which the ECM is trying to control the idle speed.

When I first used the Tech-1, I noticed that the value of this parameter started at about 2500 rpm with the engine cold (known as "Open Loop Mode"). According to the manual, this number varies and depends on the coolant temperature. Once the engine warms up and switches to Closed Loop operation, the number drops to 985 rpm.

The Tech-1 is bi-directional, and thus allows you to change the value of this parameter using the Up and Down buttons (although, I personally, did not try it). The problem is that since this value changes based on Open/Closed Loop state of the ECM, I suspect that it gets the numbers (particularly the Closed Loop one) from its ROM tables in the Mem-Cal cartridge.

If this is indeed true, it means that once the engine cools down and then goes through another cool-to-warm cycle, the ECM will substitute the 985 value in this parameter again and you'll have to repeat the process. So, unless you want to drive around with a Tech-1 hanging underneath your glovebox at all times (I've contemplated this myself), it could be kind of inconvenient.

The other option is to call someone like my buddy Steve at SuperChips, and have him make you a custom Mem-Cal with an adjusted idle parameter. Sounds like a lot of trouble to go through over a thumpy idle though. And, there may be some emissions regulations being violated, I don't know.

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Mem-Cal Software Upgrades

You can improve the performance of an Esprit SE or S4 by installing the larger turbo of the S4s and by replacing the Mem-Cal in the ECM with the one that comes in the S4s. These two upgrades together will yield about a 20-30 horsepower increase. Additionally, if you own an S4s and you have problems with engine stalling you may benefit from a newer version of the S4s software that was released by Lotus. In either case, you may obtain the new S4s Mem-Cal through Lotus Cars USA (1-800-24-LOTUS) or from my friend Sanjaya Vatuk. Prices are in the $60 to $75 (plus shipping).

Click Here for Sanj's step-by-step procedure on removing the ECM and Mem-Cal.

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