I know this has been published before, but since it gets lost on old threads, I want to show it again.
I bought an old F150 2005 with the 5.4 in it, as I did to my 2006 Expedition, I decided to check the Fuel Pump Driver Module FPDM under the bed above the spare tire.
I just don't want to get stranded when winter sets in or when I most need my truck.
I found at least 1/4 inch of salt and debris behind it.
Here is what I did to avoid issues in the future.

• I run the back of the FPDM on my grinder's wire brush to clean it, then I coated with a coat of epoxy, (JB Weld)
• Then I sanded and painted the rail where it is mounted.
• Bought a pair of stainless steel bolts washers ans spacers at Lowe's for $5

Now I don't have to worry about FPDM corrosion for a while.
Please check yours now while the weather is good (if you live in northern latitudes.)


Coat of Epoxy JB Weld on its back to prevent future corrosion.

Let it dry overnight at room a/c temp.

It now has a nice 1/4 inch gap between the module and the mounting rail.

Close up of the spacer and stainless bolt/washers.

 

The spacer is a great idea! Im not sure why Ford decided putting two different metals together like that would be a good idea .. I checked mine last year and it was pretty clean.

 

Hate to break it to ya, but you’ll still see plenty of corrosion beneath the JB weld. Electricity causes the corrosion much more than the weather, and the stainless spacers may accelerate it over rubber ones. Don’t give up checking it, it’s a decent experiment.

 

Won't the steel bolts through the aluminum(?) back, going into a steel frame still complete the galvanic circuit?

 

Yes, it would, but not as severe.

 

Yes. No change in electrolysis.

After confereing with a few engineers I know, common consensus is the standoffs actually have nothing to do with preventing corrosion but are to help cooling of the unit.

 

And why is that?

 

Not as much surface area contact between the steel frame/bolts and the FPDM's metal body.

I would imagine that to have no galvanic circuit, the smoot area of bolts would have to be coated with plastic (where it would normally touch the FPDM through the holes), and you would need a plastic washer.

 

Electrolysis is caused by electrical current not surface area. With the stock positioning of the FPDM, the only part that actually touches the frame IIRC are the bolt eyes, yet the entire device rots. As long as there is contact between two dissimilar metals, the galvanic circuit is created and corrosion will occur. Of course, any stray voltage from salt or degraded aluminum (I swear the case if this thing corrodes more like zinc; we run aluminum boats that live in salt water, and nothing corrodes nearly like the FPDM except their zincs) would exacerbate the corrosion. In chemistry terms, we call the FPDM a sacrificial metal, but at least it’ll help prevent the frame that it’s attached to from rotting. You are are correct, to prevent corrosion, insulating the bolts is necessary. My FPDM was corroded as hell after only 30k miles, with the standoffs (which don’t help prevent corrosion due to electrolysis). I firmly believe that there has to be stray voltage in the case of the thing on the ones that rot. I could show you hull plating that’s been submerged in salt water continuously since 1989 and is still brand new under the paint.

Fun fact: we just had a new $9 million dollar boat built at work. Itss zinc bricks are GONE after almost a year in the water; the other aluminum boats get several years out of their zincs. The zincs are there to prevent corrosion of the aluminum, hence sacrificial metal. Clearly, it’s got some stray voltage somewhere from its 200A generators. Your tax dollars at work.

 

When I replaced my FPDM at around 100k miles, it had just a little bit of corrosion, but it was mostly just dust (replacing it wasn't even necessary, I just did it as preventative maintenance). Up in that area, there is very little rust on the frame. Also, the factory FPDM was unpainted, but the Dorman replacement I bought had gray paint on it.

(The truck was originally sold new in Oklahoma City in 2006, then I bought it in Oklahoma City in 2009 and drove home to Texas - had to pay taxes myself when I did the registration)



--EDIT--
I think this thread should be merged into the existing stickied FPDM thread.