View Full Version : Electrical: Electric fuel pump causing interference on AM Radio

09-13-2017, 05:36 AM
After installing an electric fuel pump on my 1962 GT Hawk I noticed I was getting a cracking or popping sound from my stock AM radio while the pump was running. I turn the pump off and the noise disappears. Has anyone else had this experience and if so has anyone come up with solution to fix it?

Jeffry Cassel
09-13-2017, 07:21 AM
No. But there is so little to listen to on the radio that we seldom turn it on. Try a condenser in the pump circuit. There are also AM filters that can be installed in the radio lead.

09-13-2017, 07:39 AM
An electric motor spins quickly and has a rotating magnetic field. This can (and will) induce an electric current in any surrounding conductors. If one of those conductors functions as an antenna then you can get interference in your radio. AM is more vulnerable than FM but both can be affected. The first thing to check are grounds. It is amazing how many car electrical issues come down to bad grounds. This might too. Make sure the body of the pump is grounded to the chassis. Also make sure the body of the radio has a solid ground. Finally anything metal near the pump should be tied to ground. Try to route wiring as far from the pump as possible. It is also worth checking your antenna lead for good insulation. Keep that separated from the car's wiring as much as possible (difficult to do behind the dash!).

If none of that helps then you can try to filter the noise. A 2 mfd capacitor between the power lead and ground should help. There are commercial filters for sale but most of those are intended to go on the radio and filter out ignition noise. They might help or might not.


09-13-2017, 07:43 AM
No. But there is so little to listen to on the radio that we seldom turn it on. Try a condenser in the pump circuit. There are also AM filters that can be installed in the radio lead.

OR...you could enlist the services of "Radio Roy," or some other of our qualified members, to take your radio, convert it to AM/FM while keeping it's original appearance.:!:

It's only money...;)

09-13-2017, 01:50 PM
I was hoping that Radio Roy would see this post and respond. I plan on having it converted to am/fm this winter and back in the car before I put a Vintage heat and air package on it in early spring. I am just typing to get by with what I have until then, but the noise/static caused by the fuel pump is really bad.

09-13-2017, 04:09 PM
Where is the electric pump located? They work best pushing rather than sucking so near the gas tank is best...away from the radio though the car's steel body should provide sufficient shielding. It does sound like the radio's filtering needs replacing.

I'm not sure but isn't the antenna on some Hawks rear mounted? If so, and the pump is located close by, the antenna cable between the antenna and radio may be bad due to age and cracking. Replacing that cable could be a help.

Joshua Skinner
09-13-2017, 06:47 PM
The brushes in the fuel pump and the armature coils act as a spark gap transmitter. The wiring to the fuel pump act as the antenna. A noise suppression capacitor as Jeefry and Nathan suggest should do quite a lot to help reduce the amplitude of the noise and shielding the pump wiring would help radiate the noise less.

09-14-2017, 12:58 AM
Not all fuel pumps are rotary motors. Many have a solenoid with points and/or an electronic pulser circuit to energize/de-energize the solenoid. That will make a popping sound in the radio just like ignition points do. In any case, get a small choke coil that can pass enough current to feed the fuel pump. Toroidal chokes wound with heavy copper wire are commonplace in all sorts of equipment with switching power supplies these days, if you want to scavenge one. Mount it as close as practical to the pump, and feed the pump power through the choke. Connect a 2 uF capacitor between each end of the choke and ground. Mount the parts on a small piece of perfboard, and enclose in a small metal box. Should cost more than a couple of dollars. You have just created a "pi network" which is very popular style of filter. Putting it as close to the pump as possible reduces the length of unfiltered wire which can act as an antenna to radiate the pulse noises.

09-14-2017, 06:21 PM
I read this somewhere else, but radio interference can be quieted by running a ground wire back to the battery instead of using the chassis as ground. A simple jumper wire hooked up this way will let you know if it helps.

09-15-2017, 08:00 AM
Seems like I cured the problem with the electric fuel pump causing static over radio. I cleaned the ground from the battery to the block, the oil pressure line to the firewall, and the fuel pump ground to the frame.
I started motor, turned on the radio and the static was gone. Cheap fix.