99 5.4L Trouble in the rain

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FlyinMatt75

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It's rained pretty hard twice in the past 2 weeks where I live. Both times it has caused problems gett8ng the truck started.

1st time the expy just cranked and cracked but never fired. No water on the fusebox under the hood or inside under the dash. No visible water running down the firewall onto the engine. Did notice the vent fans would turn on without needing to insert and turn the key to "on".

2nd time the battery was totally dead. Put it on the charger and the lights dimly came on even though the headlight switch was off. Let it charge and finally started. Vent fans worked with no key again.

Both times the truck needed to sit a while after the rain to dry out some. I've checked cowl drains and they are clear. Hood seal up by the windsheild is good. I'm not seeing water in the cab either.

Anybody got some ideas where to look? Is it possible for a leak on the rear hatch to cause this much trouble?? I think I may have a leak back there. It's going to rain tomorrow so I covered the front with a tarp, so we'll see if the back is the culprit but I doubt it.

Appreciate any advice you may have!
 

rjrodney

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Google GEM module but check your alternator too. GEM is behind the fuse block in the dash. They are super notorious for getting wet from windshield leaks. Water runs down from the rusty spots under the windshield seal on top of the roofline.
 
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Dobermans

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There are a couple YouTube videos showing how to get the GEM out. After you take it out there will be a part number on it. If you replace it you need one that is already programmed for your Expedition. Take the part number that’s on it and check eBay they go for around $45 and up, make sure to get the exact part number.
 

VoxVeritatis

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"Vent fans worked with no key again."

Seriously? My 2002 Eddie Bauer 5.4L 4X4 EATC (including ventilation) only operates with the key in the "On" position or when the vehicle is running.

If this is not symptomatic of THE problem, it would certainly seem symptomatic of A problem.
 

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