Is there any general FAQ about ECUs? I have an 87 NA and am wondering what I can do to tune things up a bit. I don't understand much about the ECU and all the engine management stuff. What for example is an AFC? Might it do what I want for a very slightly modded engine, say intake, exhaust and injectors? I'd appreciate any help.

 

Aftermarket ECU's are basically divided into two groups:
1) Engine Management System (EMS) = Controls both fuel and ignition, and some auxiliary functions such as rev limiter, boost control, electric fan, etc., depending on the brand and model of the EMS.
2) Fuel Computer = Controls the fuel injectors and maybe a few other auxiliary functions, but not the ignition.

There are three types of installation:
1) Piggyback = Attaches to the stock system.
2) Plug & Play (aka Plug & Tune) = Replaces the stock ECU by plugging into the stock connectors, and uses the stock wiring and sensors.
3) Standalone = Bypasses or replaces the stock ECU and wiring.

This website is a bit dated, but some of the functions are explained well in a very brief description, and the picture of the 3D graph gives a good representation of load vs. rpm vs. injector pulsewidth.
http://www.redlinerotary.com/wolf.htm

EFI for Dummies:
http://home.clear.net.nz/pages/phil....0Operation.htm

AFC = Air Flow Converter, which means that it alters the signal from the airflow meter. You may be thinking about the Apexi Super AFC (aka S-AFC).
http://66.216.67.51/product.asp?0=208&1=245&3=251
http://www.apexi-usa.com/default.asp
It would allow you to tune the fuel injector output if you find that your air/fuel ratios need adjusting because of your engine modifications. However, since it is a piggyback computer, it still uses the slow stock ECU, so you may want to consider a full standalone EMS if you can afford it. BTW, the stock AFM isn't as bad as you may think, but the stock ECU is awful by modern ECU standards, especially on the 86-88 models.

You can browse through the various EMS websites to learn more about each product, or EMS/ECU's in general. Some sites even have manuals and software for free downloading.
http://www.aempower.com/
http://www.autronic.com/
http://www.haltech.com.au/Products/ECUs/ecus.html
http://sandstallion.com/link_wiem.html
http://www.mazkwik.com.au/products/microtech/
http://www.motec.com/
http://www.sdsefi.com/
http://www.electromotive-inc.com/
http://www.efisystems.com/
http://www.force-efi.com/felpro.htm
http://www.bgsoflex.com/megasquirt.html
http://www.wolfems.com.au/home

 

Wow! Thank you very much for the answer. I'll check out the websites and learn what I can.
One question crossed my mind. If the stock S4 ECU is particularly handicapped, could you use one from an S5 of the same model, e.g., two GXLs? I realize that there are some differences in the engines and that the S5 must have more inputs but most inputs default if the signal is lost. Just a thought.

 

You could rig an S5 ECU setup, but I don't think it's worth the effort because although the S5 ECU has twice the processor speed, it is not programmable, so you would still need a piggyback computer to tune your engine. I think you would be better off just slapping a $300 S-AFC onto your S4 ECU if you want to go the cheap route and just have something that "works". If you want something better, then just save up enough money for a budget full-function EMS like the Microtech LT8 which you can get new for under $1,000, or you could find a slightly used Haltech E6K for under $1,000. Your next step up would be the $1,400 Wolf3D 4.0 and $1,600 Haltech E11, which have 15 times the injector pulsewidth tuning of the LT8.

 

Yes, I think the AFC is the way to go; cheapest and simplest! So, as the money comes in, I'll put on a cold air intake and the AFC and see what I can do. Thanks again for your help!