Batboard

Has anyone here ever installed a radio in a 93 Oldsmobile Cutlass Ciera S? My brother is trying to get rid of horrible noise in a Maratrac installed in one. The car has the 3.3 liter V6 with fuel injection. The main power wire and the green and orange wires from the head are attached directly to the battery with secure connections. Antenna is a hard-mounted (NMO) quarter-wave. The chassis of the radio is bonded to the vehicle chassis. The problem seems to only occur on the local 2m repeater frequency, 146.820, and seems to reduce dramaticlly when the heater fan is turned to high. We have tried adding additional loads to the battery, thinking it was maybe load-related, with no success. Does not give any problems when the car is sitting still idleing, or untill the car reaches app. 20 MPH. Engine RPM doesn't seem to make any difference. Any ideas? Please??!!!?

FUEL PUMP!

Yep...had the same problem in my '89 Beretta GT with the 2.8...

Either your pump is shot, wiring is corroded or you just need to get some clip-on ferrite coils on the 12v wires to the pump, near the pump

First, try to assemble the power/ground into a twisted pair. Did you use an external noise filter?

Ferrite beads usually help only an RF intrusion problem and not audible level EMI, but you can try this.

Second. Add .01uF caps the heater blower leads. Add another cap from the blower (+) to ground and another from blower (-) to ground.

Third. Pull the fuel pump an solder bypass caps to the pump. Do a search for Crown Victoria fuel pump noise for a description.

Try the unit ground to a clean chassis ground instead of to the battery (-) since there is sometimes tremendous noise at the battery leads.

Is the coax and connectors in good condition and not pinched ?

I have to agree, sounds like a fuel pump. Also, the Ground, should be close, don't go all the way to the battery, you can pickup noise coming back down a long ground like that too, as well as the previously mentioned noise that seems to be right there.

If you have an inductive amplifier (Probe from a Tone/Probe Kit) you can use that to search for the noise too sometimes (if you know the device you know what I mean)

OK, people, thanks for the ideas! The possibility of the fuel pump causing the interference never crossed my mind, although if it is the fuel pump, would the speed of the heater fan make a difference like it does? It's worth checking out anyway, for sure. And I guess I should've made it a bit clearer that the A- lead is not tied directly to the battery, just the A+ leads. The drawer is installed under the passenger-side seat, and the A- lead, as well as the chassis ground lead, is attached with the seat-bracket bolt, which should be very well secured to the vehicle chassis. The A- lead is also only app. 2 feet long. Thanks for the suggestions! I'll post back with the results in a few days maybe.

Yes- it can. The heater motor itself may be causing the problem or.....

as the heater motor is turned on, the overall system voltage drops and causes the fuel pump to slow down and changes the pitch.

OK, Jim, didn't think about it that way. Other loads don't seem to affect it, but it still sounds like a good starting place.