Lifter Pump causing Noise in radio (AM only)

[erice1984]

Alright, I have one of those 12V lifter/helper pumps.  I believe it is a solenoid type.  Now I turn the radio on, while listening to FM I don't hear the noise from the pump, but once I switch to AM I hear it through the speakers.

My evaluation;
  Since I don't hear the noise on FM I know it is not my radio or the speaker wires.  Which leads to RFI.

Any ideas on how to fix this?  I was thinking of a flyback diode/voltage suppressor diode, to quell the voltage change within the wires that maybe causing the RFI.

Thanks
-Eric

[maxfax]

That'd probably be your best bet..   That's essentually what the manufacturers use on ignitions and charging systems to eliminate such noise...

How do you have the lift pump powered?  Using a relay and drawing power direct from the battery to isolate it's draw from the ignition switch wiring couldn't hurt either..

[erice1984]

I have it going through a relay switched by ignition like you stated.. 

[maxfax]

Bummer..  Voltage suppressing diode or a noise suppression capacitor  would probably be the next best route..   BAck in the day they just used the noise reduction capacitors which did a fair job ad absorbing the excess induced current before it fed back into the electrical system..  Now days the diode seems to be the popular choice for preventing the feedback, of course most circuits on modern cars that need this (such as the a/c clutch) are relayed, and not pulsing as much as that pump would be...  USe both and I would think that would fix it..   Diode to block the induced current from the rest of the system, and the capacitor to absorb it...

[zukgod1]

I HAVE A SOLUTION.

Dont listen to AM..   

I know I know I'm a smarta$$.

I didn't read through the above posts completely so hopeful this wasn't covered. Ground.. Better ground my friend. Ground your battery to the body better, then ground the pump to the body better as well.
Almost always a ground issue.

[erice1984]

I understand the ground problem.  The thing is, this wiring is all fresh.  I have more than enough grounds throughout the car.  In fact I ran 4 gauge from the back to the front of the car grounding it at about 4 spots along the way.

The issue is with the solenoid pump, it turns on and off about 4 or 5 times a second and causes massive amount of induction through the solenoids coils every time the pump is in the off state.  I don't know exactly how much voltage is being induced, but some sources have said in the realm of ~600volts.

better grounds only help so much, but electromagnetic induction, you just can't fight with better ground.