hi I have an 89' 5.0 L that runs awesome most of the time . some times like this morning however , it wont fire ... it cranks and cranks fast but just wont go. it has been raining for the last few days and this pattern has led me to belive that something to do with the dampness makes it a problem ? it stranded me a few years ago out sledding and made me late for work a few times so i quit driving it . its frustrating. I have had it towed to a dealer before and when it got dropped off it started fine . so they said if they couldn't trouble shoot it if its not acting up and would be a waist of money . another shop changed the plug leads and fuel filter and they figured that was it but its still speraticaly not starting . the truck only has 180,000 km on it . its probably somthing stupid does anywone have any ideas ?
thanks for any help.

 

I can't really give you a positive culprit, but I had the same problem on my '00 Expedition. It was moisture/water seeping through a super small crack in my firewall (and bottom of my windshield) causing quite a bit of shortages. It didn't usually happen until we had a decent amount of snow or rain. After a decent amount of time having a chance to dry, it would fire right up. It may very well not be this, but it is a small possibility.

 

Check the distributor Cap. There could be a crack or something letting moisture get in there and disrupting the spark.