Check your O2 sensor wiring. It gets crappy and the water gets in any connections that someone has made. I have the same problem with one of my trucks. I still have not found the problem. Heavy rain and it will run crappy. My ECU is all taped up and falling apart though....

 

I don't really have an O2 sensor , it's there but there's nothing for it to plug into

 

I read a post on here a while back that a guy was having a very simialr problem. The issue turned out to be the fuel injector wiring was corroding where the splices in the harness bring the 4 plugs into 2 wires. wish I could be more helpful than that but 99% of the time odd wet issues are corroded wiring.

 

Well you know.......it might help to figure out WHERE the o2 sensor goes and make sure it's working right to start....... And yes,what the above poster said is what I was talking about.

 

All this talk about your truck.......post some pics of this leaky beast

 

Alright guys thanks , that'll be the next thing to try

 

On my 88,the O2 sensor is inbetween the frame and the rocker panel and plugs up underneath the carpet. Should be a bung on the exhaust pipe around the tcase area.

The crimps in the harness will pass a resistance check but still not let the injectors fire.