Truck Fixed - Ready to Roll

Wasn't a fuel problem after all. The trouble code set in the computer was a loss of buss data. Translated that means that the various computer modules were not talking to the central computer. That's a basic description.

The central computer is located under the dash. The various modules, (ABS, Airbags, Instrument Cluster, et al) are located under the driver's seat. The computer, modules, and various sensors on the engine are connected by two wires called the PCI Buss. One wire is 2.5 Volt positive and the other wire is 2.5 Volt negative. The voltage pulses constantly. This is how the central computer "talks" to the modules. Each sensor is connected to its respective module by individual wires. The sensors function at a voltage rate of .5 volts. If there is a problem the voltage of a sensor will increase or decrease. This variance is picked up by the module which in turn increases or decreases the PCI buss voltage to the central computer and it will test the voltage of the sensors governed by that module. Whatever sensor does not have the proper voltage will be located and a code is set. The computer does not know what the problem is, only that the sensor voltage is outside of the voltage range indicated in the computers programming.

Since I had a total loss of communication, I knew that the problem was with the buss wires themselves, or at least it was the place to start. I also knew that I was most likely looking for a chafed wire where the insulation had been worn through by something.

First order of business was to locate the main wiring harness connectors on the engine. Schematics told me there were two. One attached to the cylinder head and the other behind the battery. Next, with the engine running you perform a very difficult procedure, you gently tug on the harness to see if there is a reaction.
When I tugged on the harness behind the battery, the engine died. BINGO.

Sure enough, the positive PCI buss wire insulation had been chafed through exposing the wire and it would touch the retaining clamp grounding it out. The clamp was missing its rubber lining that was supposed to protect the harness. A factory mistake. I disconnected the battery to prevent any voltage spikes during the repair, and disconnected the harness connector. I repaired the wire, retaped the harness, and lined the clamp with piece of rubber hose. Reconnected everything and started the engine. Tugged on the harness again and did not get any reaction as the engine continued to run normally. FIXED. I'm letting the truck sit overnight to see if there is any further reaction to water as it is raining here since it was water that collected on the bare metal of the clamp that grounded the positive wire that started all this in the first place.

Now, anyone reading this should know that I spent 25 years working on electrical systems of cars, trucks, buses and such, so as they say "don't try this at home". You could damage the central computer or one or all the modules. You don't even want to know what that could cost to repair.

Anyway, if the engine starts and runs without any problems today, I'll be satisfied that the problem is repaired and go back in service.