1987 R20 w/454 TBI motor not starting after heavy rain

[JensenHealey]

I have been struggling with a no-start issue on my 1987 R20 with 454TBI motor after a heavy rain storm. I have tried replacing the ignition wires multiple times with no change in behavior. The weather has to pretty warm for a day or two after a rain storm for the truck to start again. Today is two days after a rain storm here but the temps have been in the high thirties or low forties so today I am still stranded with a non-starting truck.

BTW, if I pop the hood, remove the air cleaner assembly and carefully watch the TBI injectors while cranking the motor I do see fuel being squirted into the TB so I am fairly well convinced it is an issue with the spark rather than a fuel problem.

On dry days the truck always starts quite easily.

Any suggestions would be most welcome.

[bd]

Remove the distributor cap, flip it over, and check for condensation inside the cap.  Remove the coil wire from the cap and cautiously hold it about 1/4" away from bare metal as an assistant cranks the engine to check for spark.  Be careful to not get nailed by the spark.

[JensenHealey]

OK, I will go out and try this now. No assistant here but I can try to look at the cap.
Thanks for the suggestions.

[berserk]

If you have to, Harbor Freight has a starter bump switch. You can attach the leads under the hood and with the key on use the bump button to turn the engine.