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Discussion Starter · #1 · (Edited)
I posted about this in another thread that could be related, but didn't seem to be getting much action, so I figured I would make it's own thread.

My Taurus has been recently having problems maintaining a smooth idle and seems to be related to the headlights and dome light dimming/brightening in a sort-of random flicker/short fashion. This problem only happens when the car is below 1000rpm.

At first, i thought it might be a vacuum/fuel/sensor problem causing the rough idle, therefore causing the alternator to pop in and out of a charging state. (when the alternator drops below 600 rpm, it may stop charging the system). I tried replacing the wires, plugs, coil pack, alternator, battery, mass air flow sensor, idle air control valve, injectors, checked compression on all cylinders, and everything is running PERFECTLY, other than the dimming lights. I took the vehicle to the ford dealer and they flashed the computer, ran a whole battery of tests on the car and found nothing wrong. I'm not getting any codes, all cylinders are firing properly, injectors are within range, fuel pump is providing the correct pressure, etc.

Everything I've done points to an arbitrary power draw from a circuit in the car causing increased load on the alternator and slowing the engine down, causing the system to compensate and provide increased idle speed. The problem is very much like turning the rear defrost on and off very fast. When the defrost is turned on, it dims the lights and slows the engine down for a brief second until the idle speed compensates for the new load and brings it back to ~700 rpm like it should.

With the defrost OFF, the lights faintly flicker and idle speed fluctuates ~100 rpm constantly trying to compensate. Sometimes, the flicker goes away completely and the engine idles at almost EXACTLY 700 RPM until the flickering returns and the engine responds, so I know the idle/flicker problems go hand-in-hand.

Other than throwing parts at this issue, I have taken out one of the headlights and measured the voltage at the headlight plug and noticed that when the flickering isn't happening, the voltage at the light maintains ~14.2v, but when it's flickering, the voltage fluctuates from 13.2v to 14.3v. When the flickering isn't happening, and i turn the rear defrost on and off, the voltage also jumps between ~13-14v and also causes the idle to readjust.

I have, one-by-one, removed almost every fuse to try and narrow down the circuit causing the problem at no avail. (there are some circuits that i cannot disconnect, such as the fuel pump). I have tested the ground to the body and engine and when the car is off, voltage is perfect. When the car is running and flickering, voltage pops between 13 and 14v.

I am at the end of my rope with this problem and have no other avenues to explore, so here I am, hoping beyond hope that someone on these forums will have a similar experience or solution for my problem.

Edit: Also, I've read that disabling the DRL (daytime running lights) could solve the problem. However, the 2006 seems to have the DRL module integrated with the computer, so it's not possible to just pull a fuse and disable it. I am also inclined to believe that it's not the DRL because the flickering doesn't go away when i turn my lights to the on position.
 

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When you say flickering, do you mean a rapid flicker of the brightness, or dimming with the idle drop? A rapid flicker would be an indicator of a failing diode pack in the alternator, and you're getting AC surges through the charge system.
 

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At the many hundred Hz the alternator operates at, you would not notice that flicker. The battery also would be sort of like a giant capacitor and would filter most of the AC out.

Check the voltage drop from battery ground (the terminal of the battery, not the cable clamp) to engine block while it's running. Any more than 0.2 indicates a bad ground. Also check the small wires on the alt. for contamination causing the regulator to misbehave.
 

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Discussion Starter · #5 ·
When you say flickering, do you mean a rapid flicker of the brightness, or dimming with the idle drop? A rapid flicker would be an indicator of a failing diode pack in the alternator, and you're getting AC surges through the charge system.
It's a dimming of the lights sporadically pulsing 3 times a second or 1 time every couple or so seconds and a variation in between. This, i believe, increases the load on the engine through the alternator that causes it to have to constantly readjust the idle.

I've replaced the alternator... :(
 

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Discussion Starter · #6 · (Edited)
At the many hundred Hz the alternator operates at, you would not notice that flicker. The battery also would be sort of like a giant capacitor and would filter most of the AC out.

Check the voltage drop from battery ground (the terminal of the battery, not the cable clamp) to engine block while it's running. Any more than 0.2 indicates a bad ground. Also check the small wires on the alt. for contamination causing the regulator to misbehave.
you mean compare the voltage from terminal>terminal on the battery to the terminal>engineblock and 0.2 voltage difference would indicate bad ground?

edit: i just tested from battery terminal>terminal, it sits at 14.30v-14.35v pretty consistantly, except when the lights are dimming, and it starts dropping it to 14.10-14.15v.... Sorta spiking from ~14.1v to ~14.3v while the lights dim in concert. I tried from + term on the battery to the engine block and the voltages are the exact same ranges.
 

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Discussion Starter · #9 ·
I think he meant from neg. batt. post to eng. block?
he said check "the voltage drop". If everything is working properly, checking voltage from the neg terminal on the battery to the engine block would produce a reading of 0.0v.....

Am i looking for resistance, then?
 

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You will never get a voltage drop of zero due to the (very low) resistance of the wire / connectors, but the drop should be low..... .1 to .2 V maximum under high load (blower on high, lights on, etc). The resistance is so low it is difficult to measure directly without special equipment, but voltage drop is proportional to resistance (our friend Ohms Law).

Also check drop from alternator to batt pos terminal. Easy on a Vulcan, no so easy on a Duratec. Be sure the engine to frame ground strap is in good shape and connections are clean and tight.
 

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Discussion Starter · #11 · (Edited)
You will never get a voltage drop of zero due to the (very low) resistance of the wire / connectors, but the drop should be low..... .1 to .2 V maximum under high load (blower on high, lights on, etc). The resistance is so low it is difficult to measure directly without special equipment, but voltage drop is proportional to resistance (our friend Ohms Law).

Also check drop from alternator to batt pos terminal. Easy on a Vulcan, no so easy on a Duratec. Be sure the engine to frame ground strap is in good shape and connections are clean and tight.
I am totally confused.....

So I set the multimeter to read dc volts... put one of the leads on the negative post, and one on the engine block? and i'm looking for an actual voltage, then? As opposed to 0.0 that it should be??

I feel retarded right now because I'm not sure what you mean by "voltage drop"...

edit: ok so i measured 0.02V from the neg term on the battery to the engine block. I've also checked resistance between the neg post on the battery to the body and got 0.6ohms. also i checked resistance between the negative term of the battery to the engine block and got roughly the same thing.
 

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Mine has been doing that at random since I bought it over 3 years ago. When it was under warranty, I took mine to 2 dealers, they both checked everything out, and could not find anything wrong. I even test drove 3 other Taurus just like mine, one a '07, the other two were '06's, and all 3 cars did the same wierd idle thing mine does. I think Ford changed something on the Vulcan engine in '06 that causes the idle to bounce around about 50rpms. I wonder if Ranger owners are having the same problem with their Vulcan engines? I own a code scanner with live data, all my sensors, injector pulses, etc, everything is good, except for the bouncy idle speed (you can see it better on the scanner). 3 master mechanics and myself can't find anything wrong with it. Half the time mine will idle wierd, the other half my Taurus thinks it's a Honda, and idles smooth as butter, so the issue is a random thing on these cars. I haven't bought a Mazda yet, or bothered to throw parts at it, instead I learned to live with it. It would be nice if somebody could have a answer to this issue that seems to occur on '06-'07 years, other than the tsb on the '06 year only for the pcm re-flash. I now have 115k on mine, and it still runs very well, and idles well when it wants to. I haven't had to replace the alternator yet, and mine is still putting out good charge, whether it idles normal or not.
 

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Discussion Starter · #13 ·
Mine has been doing that at random since I bought it over 3 years ago. When it was under warranty, I took mine to 2 dealers, they both checked everything out, and could not find anything wrong. I even test drove 3 other Taurus just like mine, one a '07, the other two were '06's, and all 3 cars did the same wierd idle thing mine does. I think Ford changed something on the Vulcan engine in '06 that causes the idle to bounce around about 50rpms. I wonder if Ranger owners are having the same problem with their Vulcan engines? I own a code scanner with live data, all my sensors, injector pulses, etc, everything is good, except for the bouncy idle speed (you can see it better on the scanner). 3 master mechanics and myself can't find anything wrong with it. Half the time mine will idle wierd, the other half my Taurus thinks it's a Honda, and idles smooth as butter, so the issue is a random thing on these cars. I haven't bought a Mazda yet, or bothered to throw parts at it, instead I learned to live with it. It would be nice if somebody could have a answer to this issue that seems to occur on '06-'07 years, other than the tsb on the '06 year only for the pcm re-flash. I now have 115k on mine, and it still runs very well, and idles well when it wants to. I haven't had to replace the alternator yet, and mine is still putting out good charge, whether it idles normal or not.

I will tell you this: Either I will find and fix this problem, or I'm selling this thing. Either way, I will make sure to follow up and keep this thread up to date.

When it comes to my car, I can't stand for it to be running in any less than perfect, so ghosts like these make my wife hate my OCD.

I talked to an auto electrical specialist and they have never seen anything like it, but would gladly charge me $198 to diagnose it and tell me what it is (minus the cost to fix it). After telling the guy everything i've done to chase the problem, all he did was shrug and tell me they have a special computer that can show them the problem and help them find it, so practically no help there. :(
 

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Discussion Starter · #14 ·
I am totally confused.....

So I set the multimeter to read dc volts... put one of the leads on the negative post, and one on the engine block? and i'm looking for an actual voltage, then? As opposed to 0.0 that it should be??

I feel retarded right now because I'm not sure what you mean by "voltage drop"...

edit: ok so i measured 0.02V from the neg term on the battery to the engine block. I've also checked resistance between the neg post on the battery to the body and got 0.6ohms. also i checked resistance between the negative term of the battery to the engine block and got roughly the same thing.
am I doing this correctly??
 

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Does yours do it at random, like mine does? When you turn the defroster on, the a/c compressor will also come on (when it's above freezing), and will cycle. You will notice when the compressor is on, as the idle speed will increase with the compressor running. One trouble spot to check on the '04-up Vulcan engines is the gasket on the intake air control valve (see topic finder, '04-up vulcan stalling). That part is prone to vac leaks, but the fix is easy, using a oil filter gasket. I check mine with starting fluid every six months or so, mine hasn't started leaking, yet. I wish somebody could explain why the '06-up cars have this idle issue, Ford dosen't seem to have a clue. This flaw dosen't bother me enough to trade it in, and so far mine has been very reliable, only 3 minor problems in 115k, not bad for a american car. PS you can buy a Actron code scanner with live data for less than what the shop will charge to hook it up, and then tell you nothing. With live data, you can also check up on all the sensor values, and it can be used with other '96-up cars. There's a TSB on the '06 Taurus, re a pcm re-flash to correct this problem, but it says nothing about the '07 year.
 

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I feel retarded right now because I'm not sure what you mean by "voltage drop"...
Don't. Remember voltage is a measure of potential electrical energy at a particular point. Voltage drop is in a way a measure of resistance. At the battery source, your highest potential electrical energy exists. Further down the line after encountering resistance from long copper wires and imperfect connections, less potential electrical energy (voltage) will be available. The difference between voltage at two points in a circuit is the voltage drop. This is most useful in diagnosing poor connections or failing devices in car circuits.
 

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Discussion Starter · #17 ·
Don't. Remember voltage is a measure of potential electrical energy at a particular point. Voltage drop is in a way a measure of resistance. At the battery source, your highest potential electrical energy exists. Further down the line after encountering resistance from long copper wires and imperfect connections, less potential electrical energy (voltage) will be available. The difference between voltage at two points in a circuit is the voltage drop. This is most useful in diagnosing poor connections or failing devices in car circuits.

so, if there is >0.2 volts from the negative battery terminal to the engine block, that is obviously an excessive voltage leak (short) to the ground?

As it is, I only have 0.02v
 

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> 0.2 vdc indicates resistance in the connection.
Voltage drop is the only effective way to measure the very low resistance in large conductors.

Example: 0.2 volts while alt. is charging at 100 amps (just after starting) equals 0.002 ohms of resistance. This cannot be measured accurately directly without lab grade instruments, and most of them use this method anyway.
 

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I had this problem and recently finally corrected it. First time was under warranty and dealer replaced alternator. Second time I found battery water level was real low (I thought they were Maintenance free). A few months later it showed again and I just ignored it for about 2 years. Well my battery finally went (it stalled on me with heavy load and I was having starting problems where car would crank fine but would not fire up when cold). I replaced the battery and all problems went away and car actually has a bit more pep. I hope that helps.
 

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Discussion Starter · #20 ·
I had this problem and recently finally corrected it. First time was under warranty and dealer replaced alternator. Second time I found battery water level was real low (I thought they were Maintenance free). A few months later it showed again and I just ignored it for about 2 years. Well my battery finally went (it stalled on me with heavy load and I was having starting problems where car would crank fine but would not fire up when cold). I replaced the battery and all problems went away and car actually has a bit more pep. I hope that helps.
what is the year make and model of the car you have? Also that kind of engine does it have in it?
 
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