Got one to pick everybodys brain!

2000 F150 2wd 5.4 liter

The truck has a miss only when it rains or run thru a puddle of water.
I've changed all plugs and coils and crank sensor. Don't miss all the time just intermitly. Also no water is getting on top of motor or getting into plug holes. It is not sucking any water in motor any kind of way! My brother puts his snap on scanner on it no codes, brother is a mechanic by trade, ask local ford techs about this no answers!
like I said one to pick the brain!

Clear days runs like a champ!

 

How long ago did you change the COP's and with what brand? Did you use dielectric grease on the COP's when you changed them? Sounds like a low grade misfire which will generally NOT throw a code. I suspect a COP is weak and when there's a lot of humidity it doesn't work... but just my 2 cents. Those low grade misfires are a PITA! A new set of COP's from Global Auto or Uneeksupply are about $80!

 

thanks for the responce, coils came from Global, same miss with factory coils, used dielectric grease on ends to pugs, just changed them last week, with fresh plugs. it raining today so the miss is back. even checks ends that goes to coils just to be sure it was conneting right!

 

You used grease on the ends to the p(l)ugs? The springs? That's a no-no; the spring to plug connection needs to be clean (no grease). After coating the inside of the boot, I pull the spring past the boot and clean any grease off the spring before installing the COP. You don't want grease insulating the connection between the spring and plug.

Another thought is to check the plug to make sure it's got the right gap and otherwise a good plug. What kind of plugs did you put in there?

 

You probably got a bad coil outa the box. Not the first time thats happened. Happened to me only with the much more expensive moto blues. Did you save you old known good ones? Shoulda done that. It will throw a code if you drive it through a few cycles. When it does swap the coil with a known good one..

 

Why is that a no no....what problems occur? I'm just curious.

 

Thanks for everybodys reply.
Same miss with new plugs and coils as old plugs and coils.
A crank sensor going bad will do this, thats why I changed it. Truck has 140,000 miles on it, never had trouble with it untill this started about four months ago, but only when it rains, it misses, stuttering, then just takes off running good, till the next puddle, does it all over. Check all electrical connections to everything under hood on motor, it all looks good!
No water is being splash on motor from puddles, so as you can see it makes one scratch his head!

 

you may have used to much grease. and could have a bad coil..as stated

 

I think I found problem with my truck!
I put truck on rack at my friends shop, with motor running I started spraying water on wires from oxygen sensors to main harness to starter wires, got it to miss while on rack, it is in wire harness, now I just need the time to take it apart and see what is wrong, it is my only ride for now!

 

While googleing the same issue I stumbled upon your thread.

My 5.4L sounds crazy similar to what you've experienced. I have replaced the plugs, COPS, springs etc. Ran fine for about a week until it got humid. Then it missed like crazy again. Only seems to happen when it's humid or raining. Then if the weather dries up it runs fine again. It will even start running much better if I drive for a while, seems to dry up and run ok, but if I park and let it sit for 30-45 minutes same thing happens over again.

Won't throw any codes. So frustrating.

Hope you found the issue and can give me some guidance.

 

I was thinking water must be getting around the splash guards in the wheel wells. Somehow soaking a part of the harness somewhere. Sounds like your on the right track, keep looking. When you do find it, I put dielectric grease in the harness ends where the wires enter the back of the clips, squeeze it in there. Worked for me when I washed parts of my motor, vs trying to cover all the harnesses with baggies.

 

Ok! Problem solved!
Wires running to oxygen sensers had nicks in them from when we put longtube headers on truck, moisture was getting to wires and shorting them out on pass. side making truck miss and would not throw any codes!
Can drive truck in rain and splash the big puddles and not have to worry!
Now its time to install the cams I've got and get it dyno tuned!

 

could be a small vacuum leak causing same issues

 

I'd say vacuum leak, unless your pulling a code that clearly states a missfire.