76 possible electrical problem

[bhermes]

I posted on this a few months back but have had my 76 280 2+2 in the garage since. I started it up yesterday to get back into the problem.

I have had the car for about 1 year and it has always broken down on me about once every 3 weeks. I drive the car about 6-10 miles daily. I suspected I might have rust in the gas tank, and still might, and it was suggested that maybe I have a bad ignition module. I have replaced the fuel pump and fuel filter, voltage regulator, alternator and battery.

Here is were it gets a little odd. My wife gave me a retrosound radio for christmas and I installed shortly after. I ran a wiire directly to the battery terminal (could not find one under the dash). I drove the car a few times after installing the radio before putting it into the garage. When starting it up yesterday I noticed that when I had the car out of gear and reved the car over 1500 rpms the radio would shut off. When I let off the gas and under 1500 rpms the radio would come back on. When in gear the radio stayed on no matter the rpms.

Any thoughts if the car breaking down issue and the radio issue may be caused by the same thing?

My next step is to replace the ignition module. Side note the car as always started fine.

Any help would be appreciated.

[5thhorsemann]

Test the alternator to see if you are "full feilding" or seeing more than 14 volts at the battery terminals.

[Zed Head]

The ignition module is a very expensive thing to replace for no firm reason. You might just have electrical noise messing with your radio. New electronics expect nice clean electrical supply. A capacitor on the power line might help.

But a check of the supply voltage would be the first thing to do as 5th suggests. Your alternator might be dying.

[bhermes]

I have replaced the alternator twice. I will check this one. When I replaced the second time I also replace the voltage regulator and battery.

Any thoughts of why out of gear at 1500 rpms the electronics would have issues but not when in gear?

Thanks.

[bhermes]

Sorry last post missing some words.

Anyone have thoughts of why my radio would go off when out of gear and reving about 1500 rpms and when in gear and reving the radio stays on?

[SteveJ]

You won't get much of any answers until you come back with more data. First, download a copy of the FSM for your car. The link is in my signature. Test your electrical system with a meter per the FSM and let us know the results.

[bhermes]

OK I have downloaded the FSM. Not trying to be smart but if I can do everything in the FSM then I probably could solve the problem. I will give it a try but a little more guidance on the things I should be checking would be nice.

I thought that someone would be able to tell me how the cars rpms could impact the electrical system and the battery. I am at best a novice.

I may just need to take the car to a mechanic. I have had the car in the shop about 4 times for the breaking down issue with no results. Good mechanic generally but for this car or this problem not helping.

Thanks for the link and I will see what I can do.

[Zed Head]

Your problem is kind of bizarre. But I still think that my original suggestion is worth trying. It won't hurt anything.

"New electronics expect nice clean electrical supply. A capacitor on the power line might help."

Try a capacitor that would normally be used on the alternator power line. Or, first, check that you have a capacitor on the alternator power line. Maybe someone left it off. It's the round cylinder on the back of the alternator, about the size of a stack of 15 dimes or so.

[SteveJ]

OK I have downloaded the FSM. Not trying to be smart but if I can do everything in the FSM then I probably could solve the problem. I will give it a try but a little more guidance on the things I should be checking would be nice.

Okay, go to the EE section that describes the charging system.

Since you're a novice, you might need to read this: http://www.wikihow.com/Use-a-Multimeter.

I thought that someone would be able to tell me how the cars rpms could impact the electrical system and the battery. I am at best a novice.

http://auto.howstuffworks.com/alternator.htm

Note that alternator output is proportional to engine speed.

I may just need to take the car to a mechanic. I have had the car in the shop about 4 times for the breaking down issue with no results. Good mechanic generally but for this car or this problem not helping.

Quite a few "mechanics" today rely upon the car to diagnose itself. If the car's computer gives code X, replace part Y. If the car had X number of miles, replace these parts.

[bhermes]

Great posts. Thanks and I will begin looking deeper at the FSM and EE section. Also I will check the capacitor on the alternator.

Does the alternator output vary whether the car is in gear or out of gear? I will try and check as well.

Thanks. Any other suggestions or comments would also be appreciated.

[SteveJ]

Does the alternator output vary whether the car is in gear or out of gear? I will try and check as well.

Depending upon the loading of the engine, the injector duty cycles are the first thing that come to mind. I can't think of what else off the top of my head.

[bhermes]

Not sure if this really means anything; however, I checked the voltage at the battery.

Car off 12V

At idle or about 1000 rpms I got 14-15V

At 1500 rpms I got about 17-18V

The radio did shut off at about 1400 rpms so I am guessing that it does not like the increased voltage.

Does this mean that the alternator is supplying proper voltage to battery?

My initial issue was the car breaking down once every three weeks but would restart and run after waiting about 30 minutes. If the alternator was going bad would the car want to restart after 30 minutes.

I am now looking through the FSM.