2008 F150 Lariat 4x4 5.4 serious electrical problem. Overnight, my battery discharged and when a charger is connected - without the switch on - the tach vibrates and needle moves to 5k rpm and the fuel pump clicks. When I started pulling fuses and relays to troubleshoot, it got weirder. By pulling fuse F40 (for DRL, light switch, and body security switch) and then pulling R02 Accessory Delay relay, the fuel pump stops clicking but then the Elec Throttle Control starts chattering. I've never seen anything quite like this. Any help is appreciated.

 

Disconnect the battery, charge it, then reconnect it.

 

My money will be on the PCM being toast.

 

I'd try another battery (just borrow it from another vehicle if available) just to see if it's the battery that failed. Low voltages will cause the gauges to flicker and do all sorts of odd things.

 

This.

If your battery isn't bad then this should cure the problem. The problem you describe is due to the fact that MANY of the electrical systems in the truck are still connected to the battery and still "running" even with the truck turned off and that low voltage from the discharged battery is causing them to behave erracticly. Disconnect them battery, charge it and then reconnect it when it's fully or nearly fully charged and everything should be fine. As long as the battery isn't weak.

 

I agree with glc, except, I would have it charged then bring it a parts store and have them do a full test on the battery.

 

Battery charging is in progress. I checked the purchase date and it is time for a replacement, it has lived one year past the warranty period.

 

You may be correct. I installed a new battery and the electrical system appears to be non-functional.

 

Well before you declare me intelligent and ruin my perfectly bad reputation, I'd also be looking at the Vehicle Security Module. It controls the remote keyless entry, power locks, the electronic automatic temperature control, and the battery network. It works like a GEM only you don't have a GEM on your truck. But if the VSM isn't right, nothing in the electrical of the truck will be right. I'd take a look at that before spending any bucks for a PCM. Now for the bad news. The VSM is located behind the backrest of the rear seat. Best of luck getting that apart. When I removed mine I seriously considered dynamite.

 

Labnerd, I will do what I can to preserve your bad reputation. Should anyone on the street ask about Labnerd's advice, I'll tell them you said to rotate the air in the tires to shock the pressure sensors and bring the electrical system back to life. Meanwhile, I do appreciate the advice and will attempt to get back to troubleshooting this evening.

 

Oh, my 1995 Thunderbird (1995) was making noises in the trunk one night soon after I bought it, just sitting in the driveway. I heard it as we getting into my '07 PU to go out to dinner. I yanked the then still OEM gp 65 out of it and stopped by Advance, battery was near dead.

I have heard & talked to others whose vehicles started acting strangely just sitting … due to dead or near dead battery.

 

Problem solved. It was a failed fuel pump driver module. Just about every problem I experienced is outlined in this video: I encourage everyone to check out the broad range of videos from this Ford tech. A big thanks to all of you contributing forum members, your help is appreciated.

 

Glad you found the fix.