Code 13 = O2 Sensor.
Here's something I had saved on my computer.
TBI Trucks -
Trouble Codes
12. No reference pulses to Electronic Control Module (ECM). You will get this code when checking for error codes because the engine is not running.
13. Oxygen sensor signal stays lean during warm engine cruise, your O2 sensor could be unplugged or faulty wire.
14. High temperature indicated at engine coolant temp. sensor. Sensor could be unplugged or faulty wire.
15. Low temperature indicated at engine coolant temp. sensor
21. High voltage at throttle position sensor. Sensor could be unplugged.
22. Low voltage at throttle position sensor
23. Low temperature at manifold air temperature sensor
24. Circuit fault in vehicle speed sensor
25. High temperature at manifold air temperature sensor
29. Fault in 4th gear switch
32. Fault in exhaust gas recirculation valve diagnostic switch
33. High voltage (low vacuum) at MAP sensor.
34. Low voltage (high vacuum) at MAP sensor.
41. Cylinder select error
42. Fault at electronic spark timing circuit (sets when timing is set also, clear code and verify that it does not return.)
43. Low voltage at electronic spark timing circuit
44. Oxygen sensor lean
45. Oxygen sensor rich
46. Fault at vehicle anti-theft system
51. PROM error
52. Low voltage at oil temperature sensor
53. High voltage at battery
54. Low voltage at fuel pump OR Low voltage at Fuel pump relay
55. Problem at Electronic Control Module (ECM) - ECM failure OR Serial bus error
62. High voltage at oil temperature sensor
CLEARING THE TROUBLE CODES
Turn the key switch to the off position. To clear any trouble codes, disconnect the battery for 30 seconds or unplug the connectors to the ECM. If this is done at the battery, you may loose your preset stations on your stereo A better place to remove power is at the fuse.
For a more informative diagnastic look at your system you will need a laptop computer, and ALDL cable and a free program called winALDL from here.
http://winaldl.joby.se/[/I][/B]