Bad radio reception....

My 87 testarossa radio works great when the car is cold. Progressively worse as it warms up. Eventually, no reception.

I changed the radio unit, didn't help.

Attached an external antena. Didn't help.

Any ideas? Is there some kind of rf interpherence meter I can use to zone in on whatever is creating interference?

Put a battery powered radio in the passenger seat... Did the same...

Odd...


Bo

 

the radio in my mondial is completely broken.my question to you is if you are lucky enough to be driving a testarossa why in the world would you be listening to the radio? roll the windows down and enjoy!

 

There are various in-line suppressors / chokes / filters, etc. you can install, but they don't work that well and most of them tend to drop power to the speakers.

I would recommend disconnecting the radio from the standard (factory harness connection) power supply, which is coupled to the ignition circuit, and connecting your radio [ (+)power lead & (-)ground lead ] directly to the battery terminals (positive & negative) --- run separate wires from the dash to the battery to create dedicated leads.

The downside to this setup is that the radio will now only be controlled (switched on / off) via its own power switch ---- as it will no longer be controlled by switching on / off the ignition. Although, you can also then have the radio "on" only --- without draining any other current from the battery (accessory position, etc.) and sending power to anything else on the car. The big upside is that this direct-wire configuration will usually eliminate any and all noise (aka, interference) from your sound system and will maximize reception quality.

 

Tried that. Even put a battery powered radio in the passenger seat (boom box). Same thing happened...

Really really odd...

 

Perhaps your spark plug wires have gone bad and are creating radio interference (i.e. getting more resistive as they warm up.)

 

Oh, I see. Yes, that is somewhat strange. I would say you definitely have some sort of EMI contamination problem. As Mitch suggests, bad spark plug wires could be the problem. Finding the true source of the radiation could be tricky.

Yes, there are instruments you can buy, but they are not cheap. However, you already have a good make-shift “detector” --- your portable radio. By moving it around and positioning the antenna at various locations inside / outside your car and observing where the reception gets better and gets worse, you can zero in on approximately where the EMI is coming from ---- the worse the reception, the closer you are to the source.

In addition to HT wires in the engine bay, other frequent sources are poorly isolated radar detectors, vehicle alarm systems, cell phones (the old-school ones that are installed in the car), and other aftermarket electronic gadgets that were not installed or designed correctly.

 

Mitch's idea may be the issue at hand for you. Since the electrical interference gets worse as the car gets warmer the plug wires or ignition system seem the likely suspects. Good luck & i am looking forward to the solution for future needs.

 

Strange that he is not getting any ignition noise on the radio.

 

Yes, my thought too, which is why I am not convinced that is coming from the plug wires. Typically, the EMI signals from plug leads are rather high frequency. But, the interference that Bo is observing is a lower frequency --- down in the RF range --- as it is affecting radio reception rather than the electronics directly within the radio itself.

 

Try checking the ballast resistors to the coils, cold and then hot. They should change, but not a lot.

 

Hmm... Could be the plug wires, but they are less than 10 years old. Oddly, I have had this problem ever since I owned the car.

15 minutes into a drive, I can only get reception on 1 lousy FM station. AM goes first.

I wonder if there are any cheap RF meters at RadioShack? Changing out 12 leads, which may not solve the issue, would be painful...

Would adding resistor spark plugs help? Is there such a thing for this car?

The car does have its original 1987 FuZZ Buster radar detector. It isn't on, but is wired in... I kind of like having it in... makes me nostoalgic .

 

This would be my prime suspect --- I would try taking it out of the car completely and seeing what (difference) happens. Even though it is not switched "on", it may still be drawing standby power and emitting EM noise.

A trick for checking / isolating plug wires is to shield them temporarily by wrapping the wires with Aluminum foil --- this will block any EMI coming off them --- thus tell you whether or not the wires are causing the problem. Might be a PITA with the TR, I don't know, depends on how exposed / accessible all the plug wires are.

 

Thanks! That I can try...

Bo

 

I'll be curious ---- please do let us know what you find out

 

very interesting, Finnerty knows EM so this will be fun to watch unfold. I do wonder, is the radio making any sound, a hum or is it silent? the frequency of the hum will point to what is causing the problem, if it's the ignition system then it will change in time with the engine as it revs. if it doesn't then as David has pointed out the radar detector may be emitting a CW signal that is causing problems, possibly thru a ground short and then coupling to the antennae.

 

Thanks again, will try these tips this weekend...

The car also has a slow battery drain. Never thought about the radar detector as it is always off. It does in fact work when turned on, though... .

I am suprised that wrapping the wires in aluminum foil woud work. I thought the wires were all internally wrapped anyway...

 

there is a couple ways RF interference is generated. alternator, ignition coils & spark plugs. all those will vary in frequency based on engine speed. what is the radio doing exactly? does it effect cell phone reception?

 

Some plug wires are designed and made with built-in EMI shielding, some are not --- depends on the brand and type. However, even most of the ones (for automotive applications) that are shielded are done so rather poorly, and the shielding material generally breaks down over time quite quickly and easily......losing its original performance....which, again, typically was not adequate in the first place .

Wrapping the wires with conductive (Aluminum is cheap and easy) foil surrounds them in what is known as a "Faraday cage", which dissipates and effectively blocks transmission of most of the lower, mid-band EM spectrum --- including RF frequencies, which are the likely problem in this case.

Incidentally, the wires do not have to be wrapped individually, they can be wrapped as bundles. And, it is not critical to wrap them tightly, the wrap can be rather loose --- in fact, the "cage" effect works better if there is a significant air gap between the wires and the foil layer.

Also, if it does turn out to be the plug wires, you do not necessarily have to replace them (kind of a $$$$ fix). There are many commercial products available to cover wires in a cleaner, more permanent fashion and provide the desired EMI shielding for fairly little cost.

Here are just a few sources, but with a Google search, you will find many, many others ---- even your local Radio Shack or Hobby Store might have some on their shelf ---- just make sure you select a product that is also rated to handle the heat and oil contamination of a vehicle's engine bay (as many products are designed only for relatively clean & more temperate environments).

https://www.wirecare.com/Braided-sleeving.asp

http://www.shieldingsystems.eu/index.php?p=Products&Lang=2&grp=17

 

Sounds like you need a faster radio (PM fastradio for assistance) (j/k Dave)


BTW, be sure everything (including the radio) is properly grounded. In some early cars (like my 65 Mustang), there were interference supression devices in the wheel hubs. Also, be sure the antenna has a good cable from the radio and that the antenna mount is properly installed (insulated).