My 1995 Bronco won't start when it's humid or raining. The engine turns over and sounds like it's going to start, but it doesn't start. After sitting in the sun for a few hours it will start and run fine. It has a fairly new distributor cap and spark plugs, and has a fuel pump that is less than 2 years old. Of course, by the time it starts and I can drive it to the mechanic it is running and starting fine so they can never find the problem. Any suggestions?

 

Mine got progressively worse dying on warm humid days. I replaced everything until I finally found a poor ground. After that the new rebuilt distributor hall effect sensor was bad and it would never start. First follow the negative battery cable to the fender ground stud. Dissable and clean and be sure the stud is not truning in the fender also. I made a new stud next to it. Then check the ground cable to the frame and engine from the battery. Then the ribbon ground from the cab A/C area to the engine. A single strand of wire may test OK with a meter but may not be adequate to do the job. I was getting codes 121 and 122 from continuous memory. I'm ready for a 12 hour trip now. Check you CM codes for hints. The whole story...https://www.ford-trucks.com/forums/6...onIntermittent issues really build character.

 

Another thought...When it does not start try battery jumper cables to test each of the grounds and try to start it. For example, attach one of the jumper wires to each end of the ribbon wire running from the cab to the engine and try to start.

 

Humidity has terrible effects on resistance. I had a negative battery cable corrode from the INSIDE and had no idea until the weather turned humid in spring. I took a meter to the negative cable and had something like 400+ ohms resistance. On a piece of #4 cable that sucks!

 

Thanks for the advice - gives us some new things to look for. We just picked it up from the mechanic who couldn't duplicate the problem (but didn't charge us for looking since he's fixed so many other things on the Bronco). It's supposed to be a cool clear night so it should start in the morning................

 

my dad had a suburban that did that, turned out the dist cap had a hairline crack in it letting moisture in, i know you said the cap is fairly new but just a thought.