Battery or Alternator?

[imaz]

Hi,

I was driving in a school zone of 40k and hit the cruise control. I noticed the car kind of stalled but did not turn OFF, as I was able to feel it and still pick up by pressing the accellerator. But during this time, I saw the battery lamp lit on the dash. Later resumed to normal driving and I was okay. At the next school zone tested it out again and with the cruise I turn it on at 40km and again, the battery lamp lit up and I felt a tiny stall but did not power the engine off. Does that mean my battery is on the way out? or my alternator is not charging?

Sure the cruise control doesnt occupy that much power accessories?

[vibe_xr6]

test the battery when the car is turned off, then test it when its idling

[ThaFlash]

start the car, disconnect negitive terminal while idling, if the car konks out, your altinator is fubar if it doesn't your battery is fubar

[marg99]

Batterys sit at about 12.5 volts when not charging and about 13.5-13.8 volts when charging ( engine running)
Are you aware the owners manual says the cruise control will only work ABOVE 40 Kph so the problem may be using it at or below 40kph is causing the motor to nearly stall which will trgger the alternator light if the revs drop too low.

[imaz]

Originally Posted by marg99

Batterys sit at about 12.5 volts when not charging and about 13.5-13.8 volts when charging ( engine running)
Are you aware the owners manual says the cruise control will only work ABOVE 40 Kph so the problem may be using it at or below 40kph is causing the motor to nearly stall which will trgger the alternator light if the revs drop too low.

You might have a point. i set the cruise to say 45 and (-) it down to 40. But isnt it the same if i was to not use the cruise and just throttle to 40km with the pedal?

[XR5-Boy]

I think it's something to do with the ECU. Is it ok when you just use the pedal to maintain the 40km/h? Or is it only happening with Cruise?

[imaz]

Originally Posted by XR5-Boy

I think it's something to do with the ECU. Is it ok when you just use the pedal to maintain the 40km/h? Or is it only happening with Cruise?

I am sure its fine at 40k with the throttle and only happens with cruise control at 40km. I will try again on my drive home from the office, if it doesnt die on me.

I can crank okay and when I went to park the car at the office I turned ON the head lamps while driving with throttle at 10km, and no battery light came on.

[XR5-Boy]

Yeah, i reckon it's coz you're running the cruise at low speed. My Cougar never like that (and wouldn't even engage at or below 40km/h)

[20focus05]

For one dont disconnect battery while engine is running cause if the alt is ok you may F the ecu(no where for the current to go)
I am with XR5-Boy 40km is to low for the sytem to cope with dropping revs to low to a point where the alt is not spinning fast enough.

[20focus05]

also most mechanics have great battery/alternator testers
will test battery, alternator charge rate loaded and unloaded as well as diode test.

[REDDYZ]

It could be the transmission which is playing up. I have seen a lot, because I do on road adaptations on newly rebuilt European car transmissions. When you engage cruise control, it is forcing transmission to engage higher gear at low speeds, it is hard for engine to pull in higher gear. If car is designed to engage cruise control at lower speeds, transmission should automatically switch lower gear. Imagine what would happen when you shift to 5th at 40km/hr with a manual gear box. I would check for diagnostic trouble codes in engine and transmission just to make sure its not anything else. I dont know what is the minimum speed to engage cruise on Focus but like XR-5 boy said cruise control it is not designed to engage at lower speeds on most of the cars.

Its easy to test battery or alternator. Just test the voltage output at the battery while idling and higher rpm and see if it exceeds the specs or lower than the specs. If it does then regulator or the coil in alternator is stuffed. Stop the engine and do the same that will test the battery. Never disconnect +ve or -ve terminals while engine running. You might become the bridge for the current to pass through between battery and terminal if you are not doing it the right way. It will stuff up the electronics in the car. If not the electronics it will blow diode fuses or fusible links which can be $25 to $90 to replace. With older cars you have the freedom of doing whatever you like and thats the best thing about them.

[DZFord]

I've experienced the same in my Focus. I've mucked around with the cruise control in the past, and when the cruise fails to hold 40km/h (ie. drops below), the car nearly stalls, and the warning lights come on. Quickly adding some throttle saves the car and brings it back above 40km/h.

[imaz]

Thanks guys,

On my way home from the office today I did it again and looking at the revs at 40km(-) on the cruise control to say 35km/h you can see the rev's go down as low as 500RPM and almost about to stall. Battery lamp will light up. I am guessing anything under 40km/h is a no go for the cruice control. That is why you can not engage the cruise control at 40km/h. Only clowns like me set it above 40km/h then decrease it down further than 40km/h.

I remember reading in the manuals that it only works above 40km/h.

So in essence, the cruisecontrol must have some kind of trottling down? OR as Reddyz mentioned the Tranny can't pick up a gear. But with the foot pedal, the tranny will pickup the gears fine to cater for the lower speeds.

I guess the battery lamp lights up because the Rev's are too low(500RPM) on cruise below 40km/h, hence the accessories such as alternator spin too slow to charge battery.

Just my theory.

[baker1]

yeah you will probably find it's the cruise control drawing too many amps for the alternator to handle at such low speeds

[More revs]

Cruise control in a school zone.... sheesh..

[imaz]

Originally Posted by More revs

Cruise control in a school zone.... sheesh..

it is the only way to ensure you dont hit a speed camera in a school zone..