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Ignition noise in Ford F150
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by KE4TV on October 3, 2001
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I have a 2001 Ford F150 Harley-Davidson Edition in which I install a new Icom IC-706MKIIG and a High Sierra Antenna HD-1500MKII. I have the control head up front mounted to the center console and the transceiver mounted to the back console between the seats. If I disconnect the coax to the antenna my radio is very quite with the motor running. When I conntec the antenna I have a S-7 ignition noise. I have a good ground on the antenna to the frame and the transceiver is grounded to the body of the cab. I have considered different sparkpulg wires and such but I would like to attact the source of the problem rather than trial and error. I could spend litterly hundreds of dollars without getting rid of the problem. Does anyone one have some good sound advice? I have just bought a ClearSpeech speaker but have not installed it as of yet. I had rather get rid of the noise first. Any and all suggestions are welcome. If you konw of any good web sites that have discussion on such problems, please post them to me at ke4tv@ke4tv.com.
Thanks for any help.
Joseph
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RE: Ignition noise in Ford F150
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by W5HTW on October 3, 2001
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You have actually already diagnosed the problem. It is ignition noise being radiated and picked up by the antenna. If you can't hear ignition noise in the 706 with the antenna disconnected, and the pre-amp on, then the DC connection is clean.
So now you need to go to the next step, and that is, as you say, addressing the source. If it is ignition noise and not computer hash, then improved spark plug wires may help a lot, but may not clean it up entirely. Checking grounds at the distributor, and installing approved bypassing may also help, but you have to be careful not to install something that will damage your ignition system or computer. One good way to find out is to see if a friendly mobile radio shop will give you some free advice about what they use to suppress such noise on police vehicles. Also, though it is often hard to do, the Ford dealer may can find something that will work. All the normal techniques hams have used for years are fine, generally, but with the pecularities of computer operated ignition systems, a lot of those old shielding and bypassing procedures can actually do damage.
The point is, though, you know it is ignition noise, and you know it is being radiated. Grab a little AM pocket radio and a earpiece, and poke around with the radio under the hood (be careful not to stick it someplace dangerous!) and try to find the actual point of radiation. My guess is better spark plug wires designed specifically for the purpose will help, reducing it to a bearable level.
Good grounding is essential, and frequently grounds between engine block and frame are not as good as they should be, sometimes are extremely poor.
Poke around with the little radio. Or even connect a long "probe", made of enough RG58 to reach from the 706 to the engine compartment, but with only about one inch of center lead exposed, and the other end plugged into the HF connector on the 706. You can start with maybe six inches of center lead and trim it back to reduce the signal. I did that with a very old F150 and isolated the noise down to the source, which for me was a bad diode in the alternator, not ignition noise. Just don't let the lead actually touch anything, and most especially anything with voltage! Like the spark plug wires or a 12 volt wire!! Just use it as a "wand."
Good luck
73
ed
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RE: Ignition noise in Ford F150
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by KC5DCL on October 3, 2001
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Hi;
You did not mention if the noise changes with engin RPM or not (increase/decrease pitch/frequency). I have found that most of the time on Fords above 85 the fuel pump(AKA spark gap generator) emits an RF into most any radio, AM/FM, CB, HAM. the reason this happens is because the experts at ford failed to shield the pump in any way, also the ground for it runs to the front of the vehical(great length for an antenna). I have lessoned the effect by moving the ground to a point on the frame close to where it comes out of the tank(s) and shielding the tank(s) as much as possible (using heavy foil like flashing).
The pump(s) that are used are of the brush type roller pump, nastie little critters for us ham's
hope this helps.
Steve: KC5DCL
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RE: Ignition noise in Ford F150
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by KD5NVC on October 4, 2001
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The shielding around the pump with flashing does work, I have an F150 and shielded the pump and one more thing....I put snap-one RF choke cores around each spark plug wire. This will eliminate ALL spark plug noise.
Ford does offer an EMI RF filter install for $$$$ and the tank must come down to do this....
My shield and spark plug RF chokes do just fine for now.
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RE: Ignition noise in Ford F150
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by KC8PTB on October 4, 2001
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If you replace the wires, be careful which wires you use. Many of the aftermarket wires are much worse than the factory wires, which are carbon impregnated and have distributed resistance to eliminate RFI. Remember that Ford vehicles pass the SAE J551 RFI test, and that the folks selling aftermarket wires don't have to do that!. You might want to try making sure all the connections are solid and beware that often the conductor breaks near the plug connection. This creates a small spark gap which will run your car just fine, but ruin your radio reception. Since this is a new truck, I'd take it in to the dealer and have the wires replaced under warranty (complaint of ignition noise on your radio) this is common and not a problem. I am actually surprised that you have wires! Most of the V-8's have coil-per-plug which have no wires and is much better at RFI. There is a very good RFI filter built into the connection to the spark plug on that design.
If you want to replace wires yourself, look for the kind which use fine wire wrapped around a resistive core (Honda uses this type of wire). It is a better surpressor.
All this said, the fuel pump is also a likely culprit. Although it a brushless precision vane pump, it can be noisy. The alternator can sometimes cause this too, but usually that is conducted.
Let us know what you do!
Jim
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