Came across this site while trying to sort out issues with my 1992 GMC K3500 7.4L farm/work/daily driver flatbed truck. Currently waiting on a cable so I can see if I am smart enough to capture senor data and isolate the issue, which is Code 45, rich O2. A code I could only pull after replacing the computer which would not give any codes when jumpering A&B terminals of the ODB1. After replacing it sadly I admit to throwing parts at it, O2 sensor, temperature sensor, MAP, rebuilt TBI, distributor, coil and all grounds cleaned. At this point everything has been replaced except the fuel pump and chip in the computer. Really hoping scan data will point out what is causing the problem.