auto radio problem--AM noise

[eshort]

The radio in my 1989 Plymouth acclaim makes a staedy high buzzuing sound on am..only with the engine running..it disappears if i stop engine but leave ignition turned on--it is not a popping or whining type noise-does not change if engine is raced etc.


id like to be able to use this radio on AM 'cuase it''s very sensitive and i travel in rural areas alot!


most likely the auto's computer? Ideas?

thanx.

[Bovon]

I have dealt with many auto noises ect over the years using short wave radios, but the regular AM type of radio is more succeptable to engine type of generated noise than FM or short wave.

Try this, take some braided copper...such as what can be found just under the jacket on a piece of coaxal cable. Most any scrap yard will have some scrap coax. You might just buy a few feet of RG-8U (or RG-?U, they all have copper braid) at Radio Shack, skin it out and use just the outer layer of braided copper. Now, use a short piece of this on each side of your engine, from the engine somewhere to car frame. Keep it as short as possible. Reason?..the engine and drive train is all on rubber mounts, and any generated noise can be radiated by this 'antenna' (the drive train) I have had to bypass the engine mounts, transmission mounts and rear end with this braid to completely cure a bad case of ignition/altinator/generator noise. The use of flat copper braid is preferrable to solid copper due to its high conductance and low RF reactance.

This method will usually stop any engine compartment radio noise dead in its tracks, but...there is always that one time when it won't. In this case, you will need to find the source of the noise and use bypass filtering capacitors in the circuit.

[michaeln]

Try an ignition supresion kit. Most AM interfrence is caused by the electromagnetic discharge from the spark generated in the high tension side of things. You can get supressers for each plug lead and the coil that should greatly reduce or even eliminate the problem.

[jmichna]

Also check condition of ignition coil wire and spark plug wires. Bad insulation, especially on coil wire, can cause AM static/noise.

[TARP2]

Also check the grounding on your fuel tank. Your in tank fuel pump may be causing this problem.

[Baddog]

Hello,
Do not set or mount a mobile phone in the area of your radio.
They will interfere with it.

Baddog :t

[belgarath16]

As Bovon suggested, the interference is RFI, in a car it is generated by EMI. Chrysler had a big problem with engine grounding...a great place to start.

The AM antenna is internal to the radio, so shielding doesn't help this situation. The noise comes from the electrical system itself, and is generally caused by an A|C sine wave riding the DC supply to the unit itself. The filters you can buy at Radio Shack....etc...do a decent job of filtering out the errant signals. Get the one to install in the constant 12v as well as switched 12v supplies to the radio.

The secondary ignition is an unlikely cause do to the fact the rhythm is constant and doesn't change with engine speed...which also rules out the alternator.

Electric cooling fans, blower motors, duty cycle solenoids (PWM) can all cause it. Try turning all accessories off to eliminate the source.

The PCM (computer) is a very unlikely cause...they are loaded with clamping diodes, condensers, and filters, as well as internally shielded for EMI just like the I\O shield on your PC.
Automotive computers live in a very harsh enviroment and are duly protected.

TARP2 may also be correct about the fuel pump....a DC motor with brushes on comm that spins at 25K to 30K RPM. And doesn't change with engine speed.

Good Luck.....post reply if you need help.....I'm an auto electrical specialist.

:t

[eshort]

TX to all!!!!


I traced the noise with a pocket portable am radio--seems to be origianating sumwhere under the dash--very strong when held in front of car radio --i thot maybe the radio's LEDS-but that isnt cuase as noise only when engine running--i suspect bad grounding on car computer--but will check the fuel pump also (as it doesnt run when engine off=same time i get the no noise status)...

PS----are Chrysler electrical systems subject to early/frequent "failures" (alternators et al.).. My "Ford" friend is always telling me about Chrysler "unreliable" electronic systems!

This car= 13 years old and only 49K miles--no electrical failures yet except for this severe AM radio noise with engine on. The noise is constant..never changes pitch, intensity --only occurrs with engine running..does NOT sound like ignition based..id like to pop anothe radio in the car to see if anything changes....but fact noise absent without engine running to me strongly suggests computer or possibly the fuel pump...id think alternator but the noise pitch never changes regardless of engine speed.

[Bovon]

Originally posted by eshort
PS----are Chrysler electrical systems subject to early/frequent "failures" (alternators et al.) NO!! .. My "Ford" friend is always telling me about Chrysler "unreliable" electronic systems! People who like Fords, hate General Motors, Chrysler products ect. This is the nature of the beast. I love Chrysler products. I am running a 1989 Dodge Ram P/U with 110K miles..no failures of anykind so far. I have had Fords, Chevys ect...and they are ok, I just happen to believe Chrysler products are better. BTW, you didn't mention what engine that Plymouth has...but if it happens to be a 318 C.I., you have one of the best engines ever made, bar none.

[eshort]

its the 2.5 liter 4 cyl.

[RayH]

Try a different radio. You can get an AM-FM/CD from Aiwa for $99 and the thing doesn't skip. The AM might be a lot better than what you are trying to get to work.

[$1500-P4 gamer]

Yeah the newer players do useually have noise redustion circuitry and to top it off power filters. This helps a great deal. I get this time to time on fuel injected cars when hooking up amps even more so. The things mentioned are all correct. It can be the electric radiator fan (if you have elec. one), the ignit. coil, the alternator, the grounding of radio or amp., fuel pump if fuel injected or high output 4 barrel linkage secondarys (no vacume ****!) 1100cfm carb. with electric fuel pump to feed it (like me:D ) but thats home built engines. Anyhow they covered all the bases I was just giveing a uh, yeah me thinks so too. (not that it matters);) :t