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Old 09-25-2013, 09:56 PM   #1
Tslroper
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Charging problems (overcharging) significant amount of troubleshooting already completed

Hey guys, first post here but could really use some help. As the title states, I've already completed a significant amount of troubleshooting (I'm not blindly asking for help, and have already tried searching). By searching I found one other thread with a similar issue but no resolution was reached. I've completed most of the troubleshooting suggested there without any luck.

Here's what I'm dealing with:

My wife's 2001 zetec sedan had a fluctuating voltage at idle and was overcharging (up to 16.2 volts). I'm fairly handy with a wrench and know my way around a vehicle for the most part ( though older carbureted vehicles are my comfort area) so I replaced the alternator assuming a bad voltage regulator. No luck. I then replaced the pigtail. No luck. New battery (old one went bad, presumably from overcharging). Again, no luck. I've checked the resistance on the alternator pigtail and get no resistance on any of the wires from their tip in the connector to their termination point (+ battery for red and their respective pins at the PCM connector on the other two). So the wiring their is likely ruled out (no breaks though I suspect a short is possible). I ran a wire from the alternator pigtail red wire straight to the battery with no change. I checked all my grounds and the battery terminals and found no issues (yes I cleaned ALL of them).

Now here's the weird part: if I unplug the three wire connector at the back of the alternator with the vehicle running it immediately drops to a nice steady 14.05v and stays there though the battery light does come on.

At this point the only thing I can think of is a bad PCM (I hope it isn't so), but I'm hoping you guys can provide some input that will help me get this resolved.

Thanks!


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Old 09-26-2013, 11:55 PM   #2
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Look at the equipment you're checking with, disconnecting harness should have you not charging. If you subtract 1.5volt from every number you've given you are in the ballpark, and VOM used is in error. Not the first time I've seen it.

The volts do fluctuate on these, the PCM changes it up and down. When first starting car you always disregard any charging numbers until they max out and stay. Some can take 15-30 seconds to get there.

Check battery while car is not running, a new battery can be no higher than around 12.85 volts. That may help you zero in. Make sure car has sat overnight to do that, alt charging can give you a fake higher number, that is surface charge, it bleeds off to settle in at the hard real world number over like a couple of hours. You may see 13 volts or so if you check right after car has been running. Why at the parts store they have to bleed that off before they actually check your battery.
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Old 09-27-2013, 12:05 AM   #3
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I had the same thought, but I confirmed the voltage using 2 different multimeters, the dealer diagnostic (dashboard display) and a battery tender.

I've noticed the voltage fluctuation on start-up and accounted for that. This car seems to show 12.9ish after cranking then slowly rise to 15.5 - 15.7 where it settles in an remains fairly constant (between those two numbers for the most part).

The battery shows 12.72 volts after sitting in the car overnight (or it did this morning) before I even put the key in the ignition.

I borrowed an oscilloscope and autoenginuity (with full ford package) from a friend of mine and am going to check the waveforms on the 2 connectors running from the alternator to the PCM.

If I can find a laptop to install autoenginuity on I plan to use it to check several other things as well. The problem is I use a macbook and the software is windows only.

Given that it's putting out high voltage I keep coming back to either the 'sense' wire being the culprit or the PCM. I read somewhere about the PCM upping the voltage on a 'cold' battery for better charging based on water temp and intake air temp. Is that a European only thing or does it apply to North American foci as well? If so, could the higher voltage be a sign of a bad water temp sensor or failing MAF (IAT sensor is in MAF)?

Last edited by Tslroper; 09-27-2013 at 12:07 AM. Reason: Hit submit before I was done typing
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Old 09-27-2013, 07:18 AM   #4
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Pretty sure they ramp temp charging up and down here as well. High volts is pretty narrow cause, normally regulator but on these PCM can do it by commanding too high.

Battery looks great.

Yeah I'd be looking at sense too.
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Old 10-02-2013, 08:44 PM   #5
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Ok, small update:

The oscilloscope was largely unhelpful (primarily because I'm not familiar with how to use it). However, I replaced the battery terminals with quality terminals and noticed that when wiggling the 3 wire plug the voltage went to a steady 14.31 volts. I just replaced that darned thing so I assumed it was good. I'm order the motorcraft part and am going to bypass the harness completely by drilling a hole in the firewall and running the wires directly to the PCM. One of the wires was showing continuity to ground (very high resistance, but it certainly wasnt OFL). I'll update this thread again in about a week when the new harness arrives and i get it installed. Hopefully this resolves it and I dont need a new PCM.
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Old 10-08-2013, 02:09 PM   #6
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Ok, I drilled a hole in the firewall on the passenger side behind the glovebox, put a grommet on it ran two new wires from the PCM to the alternator plug and still no luck. The voltage stays between 14.8 and 15.15 volts but fluctuates all over in that range. The connections were all made properly with silver bearing solder and adhesive lined heat shrink. I also used a brand new motor craft plug so thats not the issue. I'm running out of ideas on this one. Any other suggestions?

On top of that, the car has suddenly developed a horrible clunking that I believe (based on research) is the strut bearings, but it came on very suddenly.

It's also not running very well over-all, just seems to be down on power and missing occasionally.

I realize these are all separate issues, so lets stick to the electrical issue. Any other ideas or suggestions?
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Old 10-08-2013, 02:53 PM   #7
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My guess is that the voltage regulator in the new alternator is bad as well. Either it came DOA, or the bad battery caused the voltage regulator in the new alternator to fry. They tend to do that. Can you get a replacement alternator under warranty? What brand do you have now and where did you get it from? You could also get your alternator tested at a parts store to see how it's charging.
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Old 10-09-2013, 01:13 PM   #8
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I believe the alternator and the voltage regulator may not be at fault here and the PCM is likely sending the wrong initialization parameters at start-up.

In post #1 you report that with the vehicle running and the connector unplugged the regulator works and you notice 14.05V on the battery. This describes a working regulator entering fail-safe mode after communication with the PCM through the serial communication link on pins 1 and 2 is interrupted. After a few seconds the PCM reports this condition by turning on the battery light in your instrumentation control panel. In this mode the target voltage is usually a default of 14.4V, and since the battery sense on pin 3 is also disconnected the regulator voltage can only regulate its own output and the voltage at the battery will be lower than the drop caused by the current load on the red cable going from the alternator to the battery, in your case 14.4 - 14.05 = 0.35V, quite reasonable.

This indicates that the generator (alternator + voltage regulator) is working correctly in such a mode (which does not use the serial link). The serial link seems also to be working since prior to disconnection the PCM reports a healthy link and correctly turns the light on after disconnection.

You can make another simple test on the generator to verify that it is indeed capable of charging correctly (and you can use this trick also as an emergency mode to try if you get stranded on the road with a nearly discharged battery). With the engine off unplug the connector, then turn the engine on. After 10 - 20 seconds you should see the battery warning light coming on as the PCM is unable to talk to the generator. At this point your voltmeter should read a battery voltage lower than 12.8V depending on the charge state and current load. Now increase the engine RPM slowly to 3000-4000 and you should see the battery voltage now over 13V as the generator enters a self-start mode. You can then return to idle and the generator will still be charging. Turn the heather blower on and or headlights and the regulator should compensate for the load although not perfectly since the battery sense is disconnected. Note that in any operational mode a fluctuation of 200-400mV should be acceptable during normal operation from what I read in the datasheet of one of the chipsets commonly used.

So far so good although there is still a remote chance that the communication link is not working properly. But at this point it is more plausible that the PCM may be sending the generator a wrong battery voltage set-point upon initialization. Your intuition on the temperature compensation here may be right. The voltage regulator target set-point is adjusted for the lead battery technology so that lower voltages are targeted at high temperatures and high voltages at low temperatures with 16V being the typical maximum value corresponding to -40F. So what if the PCM is reporting a wrong cold temperature and providing a set-point around 15-16V?

This may also be the reason for you noticing the engine not running well. In fact, fuel injection air fuel mix ratio is also adjusted to compensate from variation in air density due to air temperature (as well as for engine temperature). If the PCM believes the air temperature is say -20F it may make the mix say 25% richer with all the consequences.

You could easily prove or disprove this point by plugging an OBD2 scanner and read live IAT values and see what is reported. At the same time you can also inspect the MAF sensor which I believe contains the IAT sensor and the connector for dirt and or corrosion.

The IAT sensor in the MAF housing is a simple NTC thermistor (with resistance inversely proportional to temperature). If the NTC terminals are dirty or corroded they may cause a resistance that is higher than what the PCM expects (thus the voltage division it causes) but not enough to raise a DTC and set the engine malfunction light. A higher resistance then spells like a temperature lower than what it really is duping the PCM etc. etc. You can also disconnect and remove the MAF and measure the IAT resistance with your multi-meter before and after blowing hot air with a hair dryer and verify the resistance decreases. Not sure about the values here but according to a googled ford IAT value chart it should go from around 40Kohm to around 20Kohm (68F to 86F).

Hope this helps!

Last edited by Quark; 10-09-2013 at 03:58 PM.
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Old 12-31-2013, 03:40 PM   #9
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Holy thread revival batman!!!

Tslroper have you found a resolution to your original post? I have found myself with the exact same problem you are mentioning. I have a 2003 focus, 2.0 SPI and follows your symptoms exactly. My boyfriend has taken the steps that have been mentioned in replies and have still had zero luck.
If anyone has any further information on this problem it would be greatly appreciated.
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Old 12-31-2013, 06:44 PM   #10
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Since the thread died, I'm betting the OP found a resolution in the IAT (Intake Air Temperature) function of the MAF - either a bad connection or a malfunction of the MAF's temp. sensor.

Checking IAT with a scanner as Quark mentioned would be the quickest diagnostic for this. if the temp reported doesn't match actual air temp fairly closely you've found the problem.

Luck!
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