What the hell is a "Alternator FR Signal"

[nswst8]

Anytime I have an electrical load A/C on high at idle (Car is warmed) the idle drops dramatically then levels out but shakes/Vibrates and if I push on the brakes it gets worse.

Timing is on the mark.
Idle is perfect under no load

The honda manual indicates Alternator FR signal I just don't understand what this is.

[kcaudill]

Mine does the same thing. However mine is a Carbed model. Good luck in getting answers or suggestions, I havent got a bite yet!

[88Accord-DX]

The FR signal communicates to the ECU how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads.

The ECU compares the electrical load signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off.

[nswst8]

Or should I just replace the alternator.

As I said the car rides great, gets great gas milage and is as reliable as the day I got her.

Its just when I switch on the A/C, fan high position and then apply the brakes (Brake lights come on) when coming to a stop the idle drops to about 250rpm and seems like shes going to stall.

How do I fix this one.

[88Accord-DX]

In diagnosing some idle speed problems, alternator charging system inputs and outputs should be considered. If they’re not working properly, they may be the cause. Who would think an alternator could keep a battery charged but not allow a car to idle properly?

You’ll need a digital multimeter capable of reading duty cycle to observe this. With a warm engine at idle, all accessories off, the duty cycle should be around 30 - 35% (negative trigger). Turn on your headlights and it should go to about 55 - 60%. Switch in other accessories and the duty cycle will rise proportionately. If the electrical load is very high, (let's say you're also running a 5,000 watt stereo system) the FR signal will remain a constant 1.2V. That’s 100% duty cycle, so 1.2V is the lowest voltage you should ever be able to measure if the system is working.

I'm pretty sure by replacing the alternator it should eliminate the FR signal code.

[nswst8]

I appreciate your help, electrical is not my favorite part of cars.

I'll let you all know if this resolves my rough idle under load.

[nswst8]

The problem was poor idle under electrical load after the car was warmed up.

Solution, New Alternater the old one wasn't holding up under the electrical load. Thanks for the help Dereck. I was suspecting the alternator but didn't know what a FR Signal was.