My wife's 2003 6.0 Ex won't start. When I turn the key to On/Run (not Start), damn near everything under the hood starts making noise: sometimes the vacuum pump runs, fuel pump extra noisy, and a few other unidentified noises. And battery voltage drops to about 7 volts.

Any ideas? I know I need to replace the instrument panel cause my Acc. Delay Relay freaks out all the time, but this seems like a new issue.

 

You are having voltage problems.
Low voltage will screw up every thing.
Start with good fully charged batteries.
Then check back with an update.

 

Wow, that was it. Thanks for the heads up! This truck has been getting steadily worse, as far as little stupid things going wrong, and I just figured this was the next thing to happen.

 

I'm glad to read that your truck is doing better.
With the electronics in today's vehicles voltage at the correct amperage is almost the most important thing for them to operate.
Low voltage in my tow truck stopped it dead as the transmission would not function.
The idiot gauge on the dash showed the the "normal" position yet the alternator was putting out only 10.2 volts.
As a result the batteries discharged to being a couple boat anchors.

Have you had the alternator checked under load?
That's the culprit under the hood!

 

For the 6.0 it is very important to keep the voltage up. trying to start with low voltage or running the truck with low voltage can damage the FICM, which is a rather unreliable piece of electronics to begin with.

Because of this, I feel monitoring your voltage on the 6.0 is important. Additionally, I'm not sure if you are aware of the 6.0's penchant for damaging EGR coolers and oil coolers, but if you aren't you need to read up on it. Where I am headed is that the 6.0 factory gauges are lousy and a poor way to monitor voltage and coolant temperatures, and they have no provisions at all for oil temperatures.

I ended up buying a scan gauge II on ebay for about $100, but they are new on amazon for around $140.

If you don't have any way to monitor things, the SGII is a great way to get a monitor on just about every parameter of your engine except for EGT for a relatively cheap price. Plus it just plugs into the OBDII port so install takes literally a second, and the codes are all on their website; the 6.0 is very heavily supported. And its small so it mounts anywhere with a piece of velcro or sticky tape.

 

It's extremely important for modern completely ECU controlled cars to have proper voltage to EVERY component.

I had a friend who was having intermittent shifting problems in his 2005 BMW and after describing the problem to me I told him that with their electronically controlled automatic transmissions it was either going to be cheap or REALLY expensive to fix.

I told him to have his battery and alternator checked under load. So he took it to the dealer and asked them to check his transmission and if a bad battery could cause the problems he was having. The service writer said "no way" but while they were at it they would check his alternator and battery. The dealer couldn't find anything wrong with the transmission but they found out he had a bad cell in his battery.

They wanted to rip into the tranny but he declined and asked them to just replace the battery that was still under warranty and he never had the problem again. He was amazed that a simple battery problem could create havoc with his transmission.

If he had followed the dealer's advice he'd probably have been $5k into a transmission R&R when a simple battery replacement is what REALLY solved the problem.

 

Well yes, many cars don't work properly with low voltage. But what I'm saying is that if you operate the 6.0 with under 13 volts you will actually physically damage the FICM module and have to have it rebuilt or replaced, and its not exactly inexpensive.