924Board.org

[ted von Kampen]

My 1981 924 NA has a frequency valve, O2 sensor and a ECU 931.617.101.01 and bolted to side is a small alum box PN 477906209 which I find is called an O2 sensor relay. On the back of the alum box is two circular pin outs with the smaller having 8 pins and the larger having 13 pins. Does anyone have a diagram of what is inside and what pins are used/not used. or where can I find a description on them.
Thanks

[CRF]

It my understanding that this unit, and the simpler 4 pin one used in the 1980 are used to enrich the fuel but only at rpms under 3500, and only when the car is cold. Once the car reaches normal operating temperature, they no longer do any thing. The 1980 cars run fine without the 4 pin version plug in, but the 1981-82 control unit is wire between the ECU and the car, so you can't just remove it. As I remember it (it was a few years ago the last time I looked), the 81-82 unit has a PIC microprocessor inside, but I haven't tried to figure out how it works since it should only works for a brief time at startup.

There are four wires that are need to go between the 8 pin and 12 pin connectors to allow the ECU to work without the enrichment unit. The enrichment unit PC board that the pins are connected to have permanent connections between these four lines, so you could take the unit apart and remove the two connected PC boards and the car should run. Just be careful if you do this, I tried once and ended up breaking the PC board into several pieces. The other option is to wire up four pins between the 8 and 12 connectors. The four are: Frequency Valve 8-5 to 12-9 (brown/yellow), Full throttle switch 8-6 to 12-7 (white/black), idle switch 8-4 to 12-10 (white), just follow the wire color codes and you will be fine here. The fourth one that not so clear, but you need to connect ECU pin 5 that goes to 8-3 (brown) that goes 12-5, which is cross connected to 12-11. If ECU pin 5 is NOT connected to ground, the ECU does not generate a duty cycle. Not sure why, but I'm guessing it a safety device. On my car, the grounds from the three switches and the ground wire from 12-11 all connect to a single point on the intake manifold, and I have been told that this a common failure point, one or more of the grounds stop working.

Here is the wiring between the ECU, the acceleration enrichment unit and the car for the 81-82. I found that both the Haynes and the factory wiring diagrams were different then how my car was wired. On my car, pin 12-5 goes to engine ground and 12-7 goes to full throttle switch, factory diagram has 12-5 going to full throttle switch and they don't show 12-7 or 12-8.

Carl

ECU

1 NC
2 O2 (GREEN)
3 NC
4 O2 Gnd (?)
5 Car Sens (Brown)
6 IDLE (White)
7 FULL (White/Black)
8 Master +12 (RED)
9 NC
10 NC
11 NC
12 Acc Pin 2 (Red/Brown)
13 NC
14 Acc Pin 1 (Red/Blue)
15 FV (Brown/Yellow)
16 Master GND (BROWN, tied directly to ground)
17 Test (Black)
18 NC

ACC to ECU

1 ECU Pin 14 (Red/Blue)
2 ECU Pin 12 (Red/Brown)
3 Car Sens (Brown)
4 IDLE (White)
5 FV (Brown/Yellow)
6 FULL (White/Black)
7 GND (Brown/White, tied to ground)
8 +12 (Red/Yellow)


Acc to Engine

1 PART (White/Blue)
2 NC
3 NC
4 NC
5 Car SENs (Brown)
6 Tach (Green/White)
7 FULL (White/Black)
8 *FULL (Jumper internal to pin 7)
9 FV (Brown/Yellow)
10 IDLE (White)
11 GND (Brown, also jump to pin 5)
12 Temp (Blue/Red)

[ted von Kampen]

Carl--thanks for the detailed explanation of the wiring. I was going to ask you which pin was which number but after looking with a magnifier I saw the tiny pin numbers on the connector. So that should give me a key. It is so cold today (-7°F) that my garage is not suitable to work in. When I do get to work on it again I may have more questions. Hope you don't mind more!--Ted