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Old 12-13-2018, 11:29 PM   #1
tomj76
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Lights flickering at idle.

I have a 1996 Windstar with 3.8L engine. When the car idles, ther is noticeable flicker of the head lights, dome lights, and instrument panel. They flicker at ~7x per second. I replaced the alternator (despite testing OK), but there was no improvement. The battery is new (replacement was a little while before noticing the flicker). The flicker goes away when the rpm is increases. An oscilloscope shows that there is a voltage ripple, but it looks like about 0.5 volts p-p. The ripple frequency seems to match the flicker rate. I have cleaned the battery terminals and checked the ground between the battery and the engine block.

The alternator puts out 35 v when the B+ wire is not connected, as if the regulator is not working correctly.

I think that it is either (1) bad battery (2) bad alternator (3) broken or shorted wire.

Any ideas?

Tom
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Old 12-14-2018, 12:21 PM   #2
12Ounce
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Re: Lights flickering at idle.

My guess would be a marginally performing power relay. I don't have a diagram for your model so I can't suggest a particular relay. My 1999 has four power relays if I remember correctly ... they offer a bit of inherent delay as the battery is connected. Also they provide an easy way to segregate the electrical system during certain trouble shooting procedures. .... but if the system voltage drops a bit, such as at engine idle, they sometimes barely stay "up".
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Old 12-18-2018, 01:44 PM   #3
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Re: Lights flickering at idle.

Thanks for your reply.

I pulled some of the relays under the hood. I have not tried checking the relays under the dash just yet. I did some other testing as well. I sent the following summary of everything I have done to the alternator rebuilder (Remy Power Products)

*****
I have installed a new alternator p/n 236513 in my 1996 Ford Windstar with a 3.8l engine. The vehicle has a recently installed new battery, with good output voltage. I am experiencing flickering lights (interior, instrument panel, and headlamps) when running at idle. I have measured the output voltage (B+) using an oscilloscope, observing voltage that varies from 14 volts to 14.8 volts at ~6 Hz. If the engine rpm is increased above idle, then the flashing and ripple voltage goes away. If all electrical systems are turned on (a/c, headlights, interior lights, heating fans, radio, etc.) then the ripple is still present at idle, but the frequency is reduced to as low as 2 Hz with a significant change in engine rpm. I also observed that the case temperature increases to 110C when the load is maximized. I've checked the B+ and ground connections between the battery and alternator and found normal voltage drop over these connections.

All connections through the three pin side terminal measured OK.

I have also connected a second battery in parallel with the installed battery with no improvement.

I have pulled fuses so that only essential systems (PCM) receive electrical power with no improvement.

There is no flickering or ripple voltage when running with the alternator disconnected running only on the battery.

*****
They replied with this message:

The increased alternator temperature indicates high circuit resistance on the high amperage side. The voltage drop should be measured when the alternator is outputting as much as it can. Anything more than 0.2-0.3V on either pos or neg is the max. Also, with the alt loaded, check by backprobing the Yellow A ckt wire. No voltage drop is allowed. That will affect output voltage. We see considerable problems with Ford fusible links after only a few years of usage. A damaged fusible link could cause your flickering.

****

I have yet to check the fusible link, other than I tested the voltage on the pins of the side connector and found B+ present as expected on the two outer wires, but with the engine off and the connector pulled. I will check it again with the connector in the alternator and engine running.

-added information

Additional testing shows that the voltage drop between battery B+ to alternator B+ is 0.16 volts and battery B- to alternator case is 0.06 volts, under maximum load (all accessories turned on). However there is a significant drop from battery B+ to ckt A (yellow), as much as 0.5 volts, depending on engine RPM, with high voltage at idle that decreases to 0.1 volts at 2500 rpm. I don't see any significant drop over the 15A fuse (2mV), but most of the drop is from the fuse to the ckt A connector on the regulator.
The measured resistance of that path is small (<0.3 ohms). However, I will attempt to insert a bypass wire from B+ battery to ckt A terminal on the regulator to check for high resistance (possibly current dependent) in the ckt A wire.

*** Additional information ***

The flickering reduces significantly with a bypass wire between battery B+ and the ckt A terminal on the alternator. I also checked the current load on that wire with most accessories running and engine running at idle, which showed ~4A, so the resistance is small (0.1 ohm), but not small enough. I pierced the yellow wire to probe the voltage at each end (once near the alternator, once near the under hood electrical box) and found that the voltage drop not associated with resistance at the interface to the connectors. It looks the the wire has a bad spot in it somewhere and will need to be bypassed.

Last edited by tomj76; 12-24-2018 at 12:18 PM.
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Old 12-24-2018, 02:55 PM   #4
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Re: Lights flickering at idle.

thanks for all your follow-up .... good info!
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Old 12-26-2018, 05:02 PM   #5
tomj76
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Re: Lights flickering at idle.

Well, after further review...

I was in the process of running a shunt wire in parallel with the wire in question when I noticed that it runs through the big connector on driver side of the firewall (C100). I decided to disconnect, clean then reconnect several times to "wipe" the contacts, and with great joy I found that the voltage drop mostly disappeared and the flicker seems to have gone away.

I'll see if this lasts, but it looks good for now.
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Old 01-03-2019, 09:10 PM   #6
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Re: Lights flickering at idle.

Not to forget, 1996

"The Constant Control Relay Module (CCRM) contains the relays for the fans, fuel pump, and A/C compressor.
The PCM tells the fans to turn on.......based upon the coolant temperature or the A/C being on.
The CCRM is shown in my pictures.....mounted on the radiator support on the driver's side.
It is called by several names on part store parts list.....Computer relay, control relay, etc"

I just looked this part up on Rockauto and they now call it "Power Control Module Relay"

Newer years, 1998 and newer does NOT have this module and has separate radiator fan, fuel pump, etc relays in the relay box.

Another note for flickering lights....
I have been bit by this simple bug a few times over the years.
The battery cable connections to the battery.
I have had them LOOK perfect, and be tight....but surface corrosion caused this problem.....a light abrasive cleaning of the terminals and the inside of the battery cable surfaces that contact the battery terminal cleared it up.
Be AWARE of lead content here and wash your hands promptly.....avoid touching eyes, face.....etc with lead contaminated hands/gloves.
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Links to my pictures, intended as an aid, not a replacement for, a good repair manual.
1996 3.8L Windstar
http://www.flickr.com/photos/4157486...092975/detail/
2003 Toyota Sienna pictures (not much there yet)
http://www.flickr.com/photos/4157486...781661/detail/
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Old 01-04-2019, 05:18 PM   #7
tomj76
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Re: Lights flickering at idle.

Wiswind:

Good points. I went through checks of the battery post connections (and battery ground connections), because that was the place I first suspected. Good connections are important in those locations.

After 22 years driving in all the weather conditions that you'd encounter in places a diverse as Florida and the Great Lakes region with everywhere in between, I suppose it wasn't a complete surprise that a connector that has never been disconnected would have a few hundred milliohms of added resistance. In a similar way, I may have resolved an issue intermittent communication from the DLC connector to the ABS module.

After this very long period of service it seems logical that a few odd things will be popping up. I've recently seen that the rear ABS wheel sensors "pickup tab" has worn down to numbs from road and brake dust impacting the iron tab. The sensors don't provide a large enough signal at low speed to be recorded by the ABS module, leading to unnecessary ABS action.

On a side note, I used to have a kit to make solders by taking lead bars, melting them, and pouring the molten lead into molds. I even "enjoyed" a nasty burn one time when I dripped a bit of lead on the back of my hand. I'll bet the toy stores don't carry that one anymore, even if you could find a toy store still operating.
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