Chevrolet Repair: 89 GMC S-15 running rich, coolant temperature sensor, automatic car wash

Question
Any help on this will be great. I will tell you what I have figured out first. This problem depends on the weather. It must be cold, usually 50 degrees or below, and either raining or snowing. The engine will begin to buck at highway speeds, and if I am driving around town, it will idle high and erratically. Whenever I givie it gas it will spit and sputter, and all of the sudden it will go. Sometimes it will trip a code 45 (oxygen sensor indicates rich mixture), and flood itself out.Other times it will stop the behavior after about 10 minutes and run normally without tripping the computer. I have replaced EGR, o2 sensor (4x's),TPS, ECS, ECM, plugs, plug wires. rotor cap/button, PVC, and the entire engine was rebuilt because the excessive occurences of this rich condition had created carbon deposits on the valves making for a pathetic driving experience. The engine is set at 0 degrees for timing. Just yesterday, it was cold, about 35 degrees and I decided to take it to the car wash. I went through the automatic car wash and by the time the sprayers made their second pass at the truck it began to act up. Same symptoms, stalling, sputtering, smell of fuel. I popped the hood and noticed water around the wiring harness to firewall connection as well as around the evap canister. I am going to replace evap and try to seal the wiring harness connection. Otherwise I am stumped. It does not act up in the warm weather, at least it has not yet. Also, if it helps you, it seems to have a flat spot in the pedal regardless of weather conditions. I have also Used silicone grease to coat many electrical sensor connections to eliminate moisture entering and creating a low or high volt situation. I plan on trying new vacuum lines next. Please Advise

thank you

Craig  

Answer
Hi Craig,
I don't know what the ECS is, but coolant temperature sensor comes to mind.
I assume you have used some injector cleaner through the tank?
I wouls also check the fuel pressure, to make sure it isn't too high, as well as too low. The fuel pressure regulator is what I am thinking about here. 14PSI is what I believe yours should have.
I also have thoughts of a knock sensor keeping the timing retarded. it would be located in the block, in front of the starter.
Van