TECHNICAL NOTES ON THE EEC-IV MCU - Auto diagnostics

Eectch98-Part5.fm
be better off with 100 μF capacitor with a .1 μF disc ceramic in parallel with it.
The larger capacitor is adequate to provide the long “drinks” the CDI pulls from the
battery voltage, while the smaller disc ceramic works up to hundreds of MHz and will
help suppress the very fast rise time voltage spikes that are the true source of the
radiated noise.
Also, keep in mind that the EEC stops working when the input voltage drops below
about 8 volts -- another reason to keep a good battery and to not share power distribution
paths with the starter.
The starter and charging circuit current loop should not include the engine management
ground current loop, and vice-versa. As much as possible, the ground current
path for the alternator and the starter should be kept entirely separate from the
ground current paths for everything else. The best arrangement would be a heavy
(e.g. 2 AWG) ground wire from the battery negative to the engine block at or near
the starter and a similarly large wire from the battery positive to the starter
relay. The +12 volt power for the ECM and the accessories can be picked off at
either the starter relay or directly from the battery terminal. The ECM/accessory
ground should be taken directly from the battery negative.
Note that steel and iron are poor conductors and that much of the ECM sensing circuitry
uses the engine or chassis for grounds. To head off problems before they
start, heavy, stranded copper wire ground straps are recommended between any component
that has a sensor bolted to it (e.g. the intake or the block) and to the ground
at the battery. Solid copper tubing can be run along the chassis and/or frame and
bolted to it at several points to assure a good ground to even the remote fuel pump
and sensor -- just remember that stranded welding cable should be used anywhere the
conductor can vibrate, move or flex so it won’t break over time. (If you’re not sure
about why this is necessary, measure the resistance from some sensor’s grounded case
back to the battery ground and keep in mind that the voltage dropped across that
same path is E = I * R. So, a resistance of only .1 ohm will have one volt induced
across it if 10 amps were to travel through that path, and the resistances are often
much higher than that.)
TUNING
(by Bruce Plecan with editing by Joe Boucher and then by me)
Introduction
This purpose of this document is to assist someone in the tuning stage of an Electronic
Fuel Injection (EFI) project. It contains discussions about the monitoring
equipment required and the methods and strategies for the actual tuning. The information
is based on the experiences of tuning a GM EFI setup on a small block.
However, the methods should be applicable to most any engine.
This paper doesn’t reveal the location of the maps and tables in the ecm software
but it does discuss their functions. The maps and tables for some ecm’s can be
found on the internet. For example, the Syclone/Typhoon and the Buick T-Type fanatics
have found most, if not all, the needed information to alter the EFI systems for
the extreme modifications on their cars.
Look out, here comes a warning. You can really mess up an engine if you don’t
understand what is going on and are not careful and methodical about tuning your EFI
setup. This is not lawyer gibberish, this is for real. You can turn that expensive,
close tolerance machine into a pool of molten crap real quick. I personally
know of a kid who had too much money and not enough smarts. In the early days of
EFI, he bought an O2 sensor monitor and a device to alter the O2 feed back signal to
the ECM. He didn’t hook up the O2 monitor properly, started twisting the knob on
EEC-IV Technical Notes: Modifications/Upgrades59 last edited: 9/29/98