1985 Prom??
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
The 1985 uses the the 1226870, also know as the 870. This prom was only used for 1985. It only transmits data back and forth at 160 baud. In 1986 GM upgraded to the 1227165 which transmits data at a rate of 8192 baud. In simple terms, the 85 prom is very slow in taking samples and making corrections.
The prom itself is a computer chip that has a series of tables. The computer takes the data it collects from the engine and compares it to these tables and makes corrections to the injector impulses and other factors.
When the car first starts up it runs off these tables until operating temp is achieved and then it responds to the input collected from the sensors.
The prom itself is a computer chip that has a series of tables. The computer takes the data it collects from the engine and compares it to these tables and makes corrections to the injector impulses and other factors.
When the car first starts up it runs off these tables until operating temp is achieved and then it responds to the input collected from the sensors.
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 2
From: Huntington ma
The actual PROM chip for the ECM in an '85 is a 24 pin DIP 2732(x) 32k (4k x 8 bit) Eprom (uv eraseable) chip. These chips are considered "obsolete", but can still be purchased - either new (when you can Find some) or used/recycled. Usually they can be bought for less than $3.00.
These chips were commonly used in Arcade games in the 80's and are probably still available mostly for that reason.
The chip is held onto the main board (in the ECM) with a plastic holder. These holders are also becoming very difficult to find.
The PROM chip stores (it Is just a memory chip, afterall) a "masked" data file in binary format, 4k in size. This file contains all of the "lookup data" , tables, constants and etc, that are used by the ECM to control the engine fuel and timing. It is the data in this file that is changed (edited) during "tuning".
You would be better served to ask a question like this in the Scan and Tune section of the forum
BTW - the 160 baud date transfer rate for the 1226870 ECM is correct, but only applies to the data rate for the ALDL (assembly line data link) serial data line. It does NOT mean the ECM "talks" to its various inputs and outputs that slowly..
These chips were commonly used in Arcade games in the 80's and are probably still available mostly for that reason.
The chip is held onto the main board (in the ECM) with a plastic holder. These holders are also becoming very difficult to find.
The PROM chip stores (it Is just a memory chip, afterall) a "masked" data file in binary format, 4k in size. This file contains all of the "lookup data" , tables, constants and etc, that are used by the ECM to control the engine fuel and timing. It is the data in this file that is changed (edited) during "tuning".
You would be better served to ask a question like this in the Scan and Tune section of the forum
BTW - the 160 baud date transfer rate for the 1226870 ECM is correct, but only applies to the data rate for the ALDL (assembly line data link) serial data line. It does NOT mean the ECM "talks" to its various inputs and outputs that slowly..
