TECHNICAL NOTES ON THE EEC-IV MCU - Auto diagnostics

Eectch98-Part5.fm
only way out of not being able to tune the accelerator pump features of TBI, since
no commercial program I’ve heard of allows this to be done. However, once you have
things rather close you can try other chips from other applications, and put your
tables on them. From the good old days, a big block always took more accelerator
pump than a small block (hint).
Again rich you buy spark plugs, lean it’s internal engine parts. For Spark, not
enough timing, and you foul spark plugs, too much advance it’s internal engine
parts. (too long, too retarded, overheating)
If TPS enrichments aren’t changeable then try setting the VE high and low, (to try
having different BLs), then this BL will start to work as an enrichment during TPS
transitions. The reason this works is that the ECM will start moving the IAC counts
around.
When tuning remember the IAC is a vacuum leak. Less is better.
A Note About Timing
I have done a bunch of playing with timing especially at WOT, and lately have
noticed that 2d less than triggering the knock sensor has had no effect on performance.
In the past I’d spent lots of time doing dyno work and many times the
customer would wind up taking 2-4d out from where we had it. Please note this is in
the early 70’s, and we were using one we made, and were no where as sophisticated as
they are now. Might mention this was also getting the AFR to correct within .2
volts at each timing spec.
Try adding timing to the spark table, and remove a similar amount from the WOT spark
addition. The same with the fuel table, and WOT enrichment. When you start getting
close, change only one thing at a time, one thing only. Move two and things
might seem fine but then 2 moves later everything takes a turn for the worse and you
won’t know where to start.
Maf System Differences
On a 89 vette there aren’t really the VE tables as shown before, my example was for
a TBI which is a Speed Density. The computer knows from various sensors what is
going on but has to calculate the air entering the engine, and then fine tunes it by
using the O2 sensor. So you have to "give it a range" to estimate where to start
these calculations, and based on that a set of look ahead tables for it to consider.
Now, on an engine with a Mass Air Flow sensor the ecm is constantly being
told how much air is being used, and with that known it’s a simple calculation for
figuring the injector timing. So all it really needs is something for enrichment
for acceleration, and something for WOT. Setting up a MAF is really easy to do compared
to a MAP, if ya can get the WOT enrichments then you about have it all. Some
tinkering on the timing might be nice.
The listed items are so tightly wound together that I really don’t know how to separate
them for this document. And any one that has more to say on the subject I
would invite to comment further. Again this is from my experiences on the subject
matter, and my interruption of what others have told me, to correct difficulties
that I’ve experienced.
The ecm is a marvelous thing, but it has no self generating logic, it just follows
instructions. So it can be lied to and will never know the difference, and generates
signals we humans use as a language to understand what the computer is doing.
In other words if the computer is told to generate a WOT AFR of 13.5:1 it will do
this using the information that is feed it. So this 13.5 is a calculation, and may
or may not be an actual real world reading.
EEC-IV Technical Notes: Modifications/Upgrades67 last edited: 9/29/98