1999 Ford F150 70,000 miles 5.4 liter. Everytime it rains my truck idles rough. It happens even when the truck sits overnight and it rains. When I first start it up in the morning. The problem goes away after the weather turns sunny but always returns in the rain
Something somewhere is getting wet. You could have water getting into the intake somewhere and causing it to run rough or water in your fuel will make it do the same thing. Is it a huge difference ? Does it run rough enough to make the whole car shake ?
I had an 83 Escort that did the same thing. It would even do it in heavy fog/mist. A guy told me to take it somewhere very dark when it was doing this and pop the hood and check the wires. Sure enough, blue sparks arc'ing on the wet wires. Ran fine when dry. Might need new wires or make sure you have them properly separated.
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Dodges with the duraspark did that too.
The 5.4 has a COP ignition. Coil on plug.
If it only does it when wet I would suspect 2 areas. The front of the engine where the CAM and Crank sensors are located. If the connectors are not properly seated they can allow moisture in and cause this. Or my second guess would be the inside of tha cab. If there is a leak in the windshield area it could drip on the GEM/fuses or PCM and cause this.
Thanks for the useful tips guys. Yes it is a COP ignition and it is completely stock. I have checked unded the dash for moisture and haven't found anything wet,not to say it is not getting damp. I will check under the hood tonight. Just my luck it is pouring out,perhaps I will see some sparkin and arc'in.
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