TECHNICAL NOTES ON THE EEC-IV MCU - Auto diagnostics

Eectch98-Part2.fm
(Note that, in Intel format, the LSB is first, so it’s actually as "0054", and
54 16 = 84 10. Multiply by 8 to get 672 10.
ROM addr : Data
0x7A86 : FF
0x7A87 : FF
0x7A88 : FF
0x7A89 : FF
Speed Limiters
There are two speed limiters here, and an ON and OFF value (With hysteresis, I
think. Which means once you hit the speed limiter you need to slow down to the off
value before you can accelerate again)
When data = FF the speed limiter is off, otherwise the conversion is as follows:
0FFH --> 255, then divide by 2 and you get 127.5
Not sure which is on and which is off. Maybe someone else can help.
I think it’s
Speed Limiter A: 0x7A86 ON; 0x7A87 OFF
Speed Limiter B: 0x7A88 ON; 0x7A89 OFF
The ONs and OFFs may be swapped!
Rev Limiter
Max RPMs seems to be PIP filter related! Any thoughts here? Please post your ideas
to the EEC group.
At address 0x7C16 I have for data C103 (reverse bytes to get hi-byte first, 03C1).
H03C1 --> D961 which I think is the PIP filter. When I cut that number in half, my
rev limit is half, so it definitely affects the rev limit.
Half Fuel Limits
They aren’t used in the stang, but if you wanted a half fuel limit:
ROM addr : Data
0x7A82 : 007D half fuel ON
0x7A84 : 307F half fuel OFF
007D --> 7D00 (little endian, remember)
H7D00 = D32000 divide by 4 to get 8,000 RPMS for ON
307F --> 7F30 (little endian, remember)
H7F30 = D32560 divide by 4 to get 8,140 RPMS for OFF
Not only is this programmed above the "MAX" limit, OFF is higher than ON.
A9L Tables
(Gary Anderson wrote) "Just so you guys remember where Tom got the data:"
a9l.v5.out
"Accel Enrichment Fuel [lb/min]
EEC-IV Technical Notes: Software 39 last edited: 9/29/98