88 Pickup wont start when damp

[jodr]

88 Pickup 4x4 4cyl.

This truck wont start first thing in the morning when its been raining or its damp. Its turns over but won't start. A few hours in the sun and it starts right up.

I just had the frame repaired and they took off the gas tank and fuel pump, then put the old pump back on.

Does anyone know how I should start troubleshooting this? Can the fuel pump sending unit assembly get wet and not work ?

[fourwd1]

Is it carbed or EFI ?

[jodr]

its an EFI

[fourwd1]

That's what I figured. EFI has a whole lot of sensors that could be affected by wet conditions.
Unfortunately I can't figure which one could be causing your problem.
Any chance you checked the ECM for error codes?

[jodr]

I did not check the ECM codes. Is that a standard check ? Would that be the first troubleshooting step?

Ive got the Haynes manual here next to me. It shows EFI main relay ECU and Circuit Opening relay under the hood. Any of these a possible cluprit.

Appreciate any guidance.

[jodr]

It was a corroded distributor cap.