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Adventures Under the Hood |  |
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Adventures Under the Hood | |
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The diagnostic connectors are located at the right
side of the battery and are covered by rubber boots to
protect from splash. These connectors do not provide the
more sophisticated serial data like some of the newer
cars, but provide voltage test points for most of the key
circuits in the computer system. The connectors
themselves are standard Molex 6 and 15-pin types
available at any good electronic parts source.
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Below are diagrams of the two diagnostic connectors listing which pins do what.
Those who know how to use a good voltmeter (at least 10 megohms input impedance) may want to look farther down this page.
Note: H = system voltage (12-14 volts)
L = 0 volts (chassis ground)
Connector D1 |
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|---|---|---|---|---|
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Key On |
Engine |
Notes |
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| 1. | Tach |
L |
- |
Same tach signal as at ignition coil |
| 2. | Choke |
H |
H |
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| 3. | Ground |
L |
L |
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| 4. | Start |
L |
L |
HI only when key is in "start" position |
| 5. | Sol-Vac (after relay) |
L |
- |
HI when electric Sol-Vac is engaged |
| 6. |
- |
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Connector D2 |
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|---|---|---|---|---|
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Key On |
Running |
Notes |
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| 1 |
- |
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| 2 | Idle (Sol-Vac) Solenoid |
H |
H |
LO when vacuum solenoid energized |
| 3 | Altitude Jumper Wire |
H |
H |
Only LO if wire is grounded to block |
| 4 | B+ |
H |
H |
|
| 5 | Downstream Solenoid |
H |
H |
LO when energized |
| 6 | Wide Open Throttle Sw |
H |
H |
LO when throttle is fully open |
| 7 | Ground |
L |
L |
|
| 8 | Upstream Solenoid |
H |
H |
LO when energized |
| 9 | 10" Hg Vacuum Sw |
L |
H |
LO if below 10" manifold vacuum |
| 10 | Thermal Electric Sw |
- |
H |
HI above 65° (See 10 below) |
| 11 | Stepper Motor BØ |
- |
- |
(See 11 Below) |
| 12 | Coolant Temp Sw |
- |
L |
(See 12 below) |
| 13 | Idle Speed Relay |
H |
- |
LO when electric Sol-Vac energized |
| 14 | Stepper Motor AØ |
- |
- |
(See 11 below) |
| 15 | 4" Hg Vacuum Sw |
H |
H |
LO above 4" vacuum (See 15 below) |
10. The Thermal Electric Switch should be LO if the air cleaner air temperature is below 65° F. (nominal). In any case, it should go HI once the engine is warmed up.
11. Once the engine is warmed up and the computer is operating, the stepper motor signals should continuously alternate quickly between HI and LO. This corresponds with the movement of the metering pins in the carburetor.
12. The Coolant Temperature Switch should be HI until the engine reaches a nominal 135° F., and then should go LO as the switch closes. On my engine this happens as the temperature gauge needle has begun to move but is not yet above the "C".
15. The 4" Hg vacuum switch should be HI at idle. It is tied to ported vacuum and should go LO as the throttle is gradually opened and the ported vacuum reaches 4".
