RFI issues in the Ford Explorer

and My 2002 Sport Trac

by Pat Freeman N3GWZ

April 30, 2002

I’m a ham radio operator who enjoys using HF, VHF and UHF frequencies to communicate with other ham radio operators around the world while driving. Prior to purchasing my 2002 Explorer Sport Trac (ST), I logged many interesting conversations including US to Europe/Asia contacts using as low as 1 watt of power in Single Side Band mode! However, my ST was emitting a lot of Radio Frequency Interference preventing me from hearing most signals. In this Tech Tip, I hope to provide a unique way to fix Ford’s problem. This article should be beneficial to CB operators as well.

I first began noticing that my ham radio showed an S8 buzzing / whining noise in almost every mode, USB, LSB, AM, FM, etc. I talked with other hams that suggested building a “sniffer” in order to pinpoint where the noise is coming from. I connected a piece of coaxial cable to my ham radio with a small wire antenna at the other end and proceeded to walk around my ST while it was running, watching the S meter. At the fuel tank, the S meter showed the S8 level. Other trouble areas were under the hood and near the exhaust, but these were only S4 and lower levels. I found my culprit at the fuel tank.

Further investigation on the Internet resulted in learning that Ford had issued a Technical Service Bulletin (TSB) which informed their service departments that the fuel pump, located inside the fuel tank, was causing problems on select Ford vehicles up to 1999. TSB #9117-5 referenced installing a Filter Kit, Ford Part # E7PZ9B357A, on the power leads of the fuel pump. However, my dealer would not install this kit because the TSB was old. Another dealer ended up installing a different kit as per TSB #01-7-3, part #F1PZ18B925A under warranty. My ham radio had the same noises, however, so I had to come up with a fix of my own. Other hams suggested purchasing toroid cores and wrapping several turns of the power leads through the core. An article on the Internet referenced using type 2 toroid cores that contained a material capable of suppressing frequencies in the 2MHz to 30MHz area. However, after testing this idea, these toroids weren’t enough to stop the noise.

I finally decided to fabricate my own RFI filter by purchasing 4 of Radio Shack’s Snap-on RF Chokes, part #273-104. These chokes are square and made of a toroid material. They open in the middle to allow you to wrap several turns of wire through them. I also needed to pick up additional wire if I intended to wrap more than one turn through the choke. I picked up the red/black 18 gauge wire and some quick-disconnect butt connectors also. I wrapped the 18 gauge wire around a few chokes and installed on the power leads on my ST. My power leads were pink and black and were easily accessible when I lowered the spare tire out of the way. Check a wiring diagram or probe the wires on your Explorer with a volt meter to see which leads are correct. As shown in the pictures below, I cut the power leads and installed the butt connectors inline. This allowed me to install the homebrew RFI filter and test it. This kit worked, cutting down 80-90% of the noise! The Ford RFI filter did nothing and I do not recommend installing it. Two others have installed this kit - one on a new Explorer and another on a Ford Crown Victoria. The Explorer (2004 body style) required installation of this kit on different wires (white/black) behind the plastic interior body panel on the right rear of the vehicle.

Looking at the fuel tank.

The fuel pump power leads.

I started with two chokes and ultimately had to wire four chokes together in order to suppress the RFI being generated by the fuel pump on the power leads. I also included three T-50-2 toroids (little red “beads”) but you should be able to get satisfactory results from the chokes. I wrapped the 18 gauge wire through the chokes 7 times to create a large amount of inductance and “trap” the RFI between this filter and the fuel pump.

Filter assembly.

I installed the choke assembly inline using the butt connectors I crimped to the power leads and tested the results.

Filter assembly, installed.

I was happy with the results so I sealed the butt connectors with 3M Splicing Tape. You may want to inject some dielectric grease, available at most auto stores, into the butt connectors to prevent corrosion. I then wrapped the wires in electrical tape and zip-tied the assembly to an existing hose.

Filter assembly, completed.

I hope that this Tech Tip helps you resolve the RFI issues you might be having in your Explorer!