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Old 10-26-2012, 10:56 AM   #1
jermil01
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Intermittent Voltage drop

Figured I would start a clean thread, since I'm really not trying to troubleshoot a problem with the alternator as described in my other thread, http://www.fullsizebronco.com/forum/showthread.php?t=201035"]here

Anyway I've had this strange problem over the last year, maybe longer where the voltage gauge will drop intermittently and then recover. In the past, the battery light would come on, but that problem has since been corrected after running a new wire to the dash gauge. There is no rhyme or reason to when it happens and it doesn't do it all the time.

Battery cables are relatively new and have tight connections
Battery tested good
Grounds all appear to be ok
Alternator has checked out good
wiring from alt harness to dash gauge is new

Couple of observations, sometimes the oil pressure gauge will twitch as well, not sure if that is related.

I've pulled the cluster and checked connections and there doesn't seem to be any problem there.

Looking for any other suggestions..Rig runs great, this is just one of those nagging annoying things I wished I could figure out..
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Old 10-26-2012, 11:11 AM   #2
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remember this thread? http://www.fullsizebronco.com/forum/...d.php?t=190217

leave it alone!
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Old 10-26-2012, 03:24 PM   #3
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remember this thread? http://www.fullsizebronco.com/forum/...d.php?t=190217

leave it alone!
yes..all 30 pages of it..

what would owning a Bronco be if you weren't constantly fixing something??
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Old 10-26-2012, 04:03 PM   #4
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Use a meter to check system voltage against the gauge, and see it it's the whole system that's dropping, or if it's just the gauge reading. Those gauges are crap, anyway.
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Old 10-26-2012, 04:18 PM   #5
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Is there a way to monitor the Voltages via the ECU? Hook up a datalogger to it and then run it for a week or so hooked up to a laptop.
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Old 10-26-2012, 05:03 PM   #6
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Originally Posted by 87Roughneck View Post
Use a meter to check system voltage against the gauge, and see it it's the whole system that's dropping, or if it's just the gauge reading. Those gauges are crap, anyway.
I've done that..the aftermarket gauge I have shows that there is a drop in voltage as well.

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Is there a way to monitor the Voltages via the ECU? Hook up a datalogger to it and then run it for a week or so hooked up to a laptop.
Yes, I can do that with the datalogger on my Tweecer. I've looked at the voltage using it, and you can see fluctuations in the voltage. I just assume that is normal depending on the RPM of the engine.
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Old 10-26-2012, 07:27 PM   #7
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Jer, interesting. Two things can cause you to see a voltage drop. Either a drop in the alternator output (not likely as the regulator is all solid state), or and intermittent load increase.
(I guess that a lousy connection to the voltage gauge could make it seem that there was a voltage drop, when there really isn't.)
The only intermittent load I can think of, that is not driver caused (like pushing in the lighter, flashing the brights, etc.) is the A/C compressor clutch. Any chance the voltage drop coincides with the cycling of the compressor?
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Old 10-27-2012, 11:38 AM   #8
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yo JER,
I recall you installing a weather pack conn.
http://www.supermotors.net/registry/2896/79375
check that yet?
Also, I recall, maybe that you have a BO box or EEC-IV Monitor/Recorder?


Intermittents, Diagnosing in a 94
Some EXCERPTS:
Wiggle Testing (DCV or ohms)
Purpose: Sensitive DCV or ohms testing for intermittent harness or device.

Key off only for Ohms Wiggle; KOEO or KOER for DCV Wiggle.
Use DCV Wiggle for all actuators, power and ground signals, and all sensors which use DCV units in AUTO mode; all others use Ohms Wiggle.
Example: Ohms Wiggle MAP, PIP, INJ(S); DCV Wiggle - TP, ECT, EVR. DCV Wiggle is more sensitive than the Ohms Wiggle Test.
Select signal from PIN SELECTOR A.
Select correct ground from REFERENCE PIN SELECTOR.
Tap components, flex harness and connectors.
Wiggle Test light and beeper will activate when change sensed

The EEC-IV Monitor* and the EEC-IV Monitor Recorder* are useful tools for diagnosing intermittent driveability symptoms or Continuous DTCs which cannot be resolved through the diagnostics in Section 6A Pinpoint testing. This section supports diagnostic procedures and data using the Monitor and Recorder in a symptom-oriented manner or Continuous DTC manner.

By definition "intermittent" is a randomly occurring drive symptom for which no hard DTCs (KOEO, KOER) are revealed by Quick Test. Often the Quick Test results in "Pass DTCs" while the drive symptom still exists. Other results, such as Continuous Memory DTCs, will also apply to the scope of this section.

Before proceeding with the following procedure, be sure that:

Power and Grounds Check for low battery voltage.
Check starter and starter circuit for voltage.
Inspect electrical connections, wires, and harnesses.
EEC power:
VREF
VPWR/EEC power relay
EEC grounds:
SIG RTN
PWR GND
CSE GND
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Old 11-15-2012, 10:28 AM   #9
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Thanks for the info..Pretty sure the scantool I bought has procedures for doing the wiggle test..guess it can't hurt to give that a try..Going to check my grounds again, for what is probably the 4th or 5th time, but I don't think that is the problem..

Here are a couple of recent observations..Over the weekend, with a cold engine using my DVOM I checked the voltage at initial start up. Voltage across the battery was 14.24 and the voltage output from the alt was 14.20.

Now when I would look at the gauge on the dash the voltmeter is showing on the low end of the normal range, and my aftermarket is reading below 14 volts..how does that make sense?

Today while driving to work I noticed the reading on the voltmeter was lower than normal on both gauges..the gauge wasn't jumping or anything, but it almost looked like the battery was dying..then after about 10 minutes or so of driving when everything was warmed up the gauge moved right back into the middle...doesn't make sense.
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Old 11-15-2012, 12:47 PM   #10
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You can't address an engine-running voltage issue without starting at the alternator. Every connection (terminals AND grounds through the block); every circuit (run of wire); and internal functions. Are you still running a 2G? (Your signature pic duplicates some of the info in your profile, so put new info in.) Once you eliminate that, you can start looking at loads that might be causing the drop. What electrical devices are mounted to the body? Is the body THOROUGHLY grounded all the way to the battery?
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Old 11-15-2012, 02:45 PM   #11
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Running a 3G alt, http://www.fullsizebronco.com/forum/...d.php?t=201035. Have been for several years.

Besides the fact that I have a 3G, what info is relevant to this thread that's not in my profile?

As far as I know there is nothing wrong with my ground to the block.

Not sure what you mean by electrical devices mounted to the body? No winch, but I do have a pair of Hella 500 off lights in the front and a pair of 50 watt lights in the back, both of which are mounted to relays.

How does one determine if the body is "thoroughly" grounded to the battery?
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Old 11-15-2012, 03:40 PM   #12
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yo J,
Many times an engine to firewall ground strap is disconnected or left off after an engine or transmission overhaul; or damaged/loose, corroded."
Ford describes it as the Radio Suppression Bond (Cab-to-Frame)


see other ground locations for 92 and through 96 @ http://www.broncolinks.com/index.php?index=408

such as;
A. Starter mounting bolt B. Right front of Engine compartment near the battery C. Lower left front of engine D. Right front of engine compartment on upper radiator support. E. Left front of engine compartment Upper radiator support F. Bottom of cowl panel G. Rear of left fender apron H. Behind bottom of right cowl panel I. Left rear corner of cargo area near rear lamp assembly J. Under center rear of vehicle on rear cross member..."
by BroncoJoe19 (Joe)

"...Frame ground just inboard of the R spring tower. The black battery wire goes from the front bolt of the engine mount (on the block) to this tab & up to the battery post, where a smaller black wire goes to the core support, providing a continuous ground path between the engine, frame, battery, & body..."
Source: by CodysBigBlueBronco

Intake Manifold to Block Strap & Wire that goes to firewall pic in a 96 5.0
Source: by miesk5 at http://broncozone.com/uploads/galler...059_723748.jpg

Use your DVOM to do a voltage drop test to check for poor grounds; negative lead to the negative side of the battery and the positive lead to a good ground location on your engine block and note the voltage while cranking the engine. Check body ground by placing positive test lead to the body & turn on all lights and accessories, note the voltage reading. Anything above 0.2 volts indicates excessive resistance in the ground connection or ground cable.
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Old 11-16-2012, 01:16 AM   #13
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Besides the fact that I have a 3G, what info is relevant to this thread that's not in my profile?
I couldn't begin to guess. Without KNOWING what all your mods are, I can't determine which of them are relevant to this thread. That's why, if you're gonna ask questions about your truck, it's important to keep an up-to-date list of mods in your signature.
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As far as I know there is nothing wrong with my ground to the block.
Then you need to check it. Either there IS something wrong with it, or there ISN'T. Only you can find out for sure, so find out.
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Originally Posted by jermil01 View Post
Not sure what you mean by electrical devices mounted to the body? No winch...
Well, I'm glad to hear you haven't mounted a winch to the body! Amp? Inverter? OBA compressor? Anything that uses a significant amount of current (like >10A) and is grounded to the sheet metal.
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...I do have a pair of Hella 500 off lights in the front and a pair of 50 watt lights in the back, both of which are mounted to relays.
They're not "mounted to relays"; they may be powered through relays, but the issue is where they're grounded. Are they grounded to the frame (bumper/grille guard) or to the body?

BTW
50W @12-14VDC is ~4A, so not much of a load unless there are several.
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How does one determine if the body is "thoroughly" grounded to the battery?
Since the issue is a voltage flutter, the best way to check is by measuring voltage between the body (specifically, the cowl since that's where the volt gauge grounds) & the battery (-) post WHILE there's a heavy electrical load on the body. This is slightly older than your truck, but it should be pretty close:



Note the grounds labelled "BODY"; specifically those on the body TUB (those on the L fender, hood, or core support aren't as important). The gauges ground to the R kick; the blower, cigar lighter, power point, t/g window motor, & door window motors are the heavier loads grounded to the L kick. So operate as many of those loads simultaneously as possible to put a big load on the body ground, and see if there's any voltage between the body tub & the battery ground. If there is, you have high resistance between the tub & the R fender, or the black wire to G101 (labelled in green in this pic) is broken.

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Old 11-16-2012, 08:28 AM   #14
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yo J,
Ignore 4WABS
Locations & Components in a 96; SEE DIAGRAMS
Source: by miesk5 at Ford Bronco Zone Forums
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Old 11-19-2012, 05:58 PM   #15
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The only accessories, besides the aforementioned lights are a couple of after market gauges.

And yes Steve, the lights are powered by the relays not mounted to them..as always thank you for the correction...

"Since the issue is a voltage flutter, the best way to check is by measuring voltage between the body (specifically, the cowl since that's where the volt gauge grounds) & the battery (-) post WHILE there's a heavy electrical load on the body. This is slightly older than your truck, but it should be pretty close"

Where is this ground for the volt gauge? You mention the cowl, but I thought it's behind the right kick..can you give me a better frame of reference?

On the plus side, this is what I did find after checking all of my grounds again..this wire comes off of the negative post of battery and goes to fender wall. It pulled right out of it's connection at the battery..

So I got a new eyelet, crimped it nice and tight. Engine started right up and the gauge seemed ok, have't had a chance to drive it yet, but I'd also like to check the volt gauge ground.







New connection..

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Old 11-19-2012, 09:36 PM   #16
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Where is this ground for the volt gauge? You mention the cowl, but I thought it's behind the right kick..can you give me a better frame of reference?
Did you look at that diagram? Each location is labelled, and I think the gauges are in the lower R corner of the diagram. The cowl is the firewall, all the way back to the door openings, so the kick is part of the cowl.
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...this wire comes off of the negative post of battery and goes to fender wall. It pulled right out of it's connection at the battery.
That's probably it! But it would be MUCH better if you soldered that wire into the back of the terminal, where it belongs. That little ring isn't making a very good connection since its connection ultimately depends on the bolt which is effectively "loose" in the ears of the terminal. We all know how corrosion grows between the bolt & the terminal...
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Old 11-20-2012, 08:55 AM   #17
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yo J,
Voltmeter Ground is G200; ground is inside passenger side kick panel

Here is the wiring diagram for 92
-------

And it appears that too many wire strands are cut-off and not crimped inside the lug
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Old 11-24-2012, 02:03 PM   #18
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Quote:
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Did you look at that diagram? Each location is labelled, and I think the gauges are in the lower R corner of the diagram. The cowl is the firewall, all the way back to the door openings, so the kick is part of the cowl.That's probably it! But it would be MUCH better if you soldered that wire into the back of the terminal, where it belongs. That little ring isn't making a very good connection since its connection ultimately depends on the bolt which is effectively "loose" in the ears of the terminal. We all know how corrosion grows between the bolt & the terminal...

The diagram makes sense now. Checked both grounds again G201 and G200. Passenger side was good, nice and tight..drivers side was not..the bolt holding the ground wire to the body was pretty loose..who knows, that could have been part of the problem as well. Good suggestion on soldering the connection..

Quote:
Originally Posted by miesk5 View Post
yo J,
Voltmeter Ground is G200; ground is inside passenger side kick panel
Thanks.
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Old 11-24-2012, 02:11 PM   #19
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Now another issue came up..not sure if it's related to this voltage drop. I don't take the Bronco out too much at night so the headlights don't get used that often..

It had already gotten dark when I was leaving the house. Started the engine and then went to pull the switch for the lights. As I pulled the switch, I could see a big voltage drop on the dash gauge and then the engine almost died for a split second, almost like the power had been cut off to it...I'd never had this happen before, is it possible I have a bad headlight switch or something??

Strange thing is that it only did it the first time the switch was pulled, if I turned the lights off and on again it didn't do it..
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Old 11-25-2012, 01:20 PM   #20
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yo J,
Could be a bad switch and a bad situation;
Switch Fires, Part Number SW-2103: "...Over the past two years, this office has experienced fires caused by another potential problem in Ford vehicles. The problem exists within the dimmer portion of the headlight switch in Ford vehicles. The light switch involved is a Model SW-2103. These are the pull out type headlight switches usually located in the lower left corner of the front dash of Ford vehicles. The headlight portion of the switch has two pullout positions, the first for parking lights only, and fully out for headlights and parking lights. The shaft of this pull-out light switch can be turned clockwise and counterclockwise which activates a dimmer switch, lowering and raising the intensity of the lighting in the instrument panels respectively. Fully rotating the shaft counterclockwise past a notch activates the interior lights within the vehicles. The potential problem exists within the dimmer portion of this switch. The dimmer mechanism consists of a metallic resistive coil set inside a ceramic disc positioned over the shaft of the switch. The coil is exposed on its front side away from the passenger compartment. The front side of the coil passes across a contact permitting a current to flow through a certain portion of the coil when the switch is pulled our in its first or second positions. The greater amount of coil through which the current is permitted to pass (clockwise most position) creates the greatest resistance and therefore dims the dash lighting to its lowest intensity. The opposite position provides greatest intensity. Through our investigations, we have found that the coil can fail owing to wear and/or possible material defects or damage. A fractured coil can maneuver itself free of the ceramic disc permitting it to come in contact with the metal bracket which mounts and grounds the switch to the vehicle. When this occurs, a current can flow through a portion of the coil creating high temperatures melting the metal material of the coil and possibly igniting surrounding combustibles. This mechanism has been observed in three separate incidents by this office. Two of these resulted in a fire. The mechanism is precipitated by wear and/or defect in the coil mechanism. If the former is true, we expect there will be an increase in fires caused through this mechanism given an increase in service time. To this date the problem appears to be somewhat limited. However, this particular light switch has been utilized in numerous Ford vehicles. Therefore, a small increase in failure rate owing to age and wear could result in a significant increase in fire losses. The SW-2103 Light Switch Assembly discussed above is reportedly installed in the following Ford vehicles: 1986 -1997 F100, F150, F300; 1990-1994 Explorer; 1987-1994 Ranger; 1987-1990 Bronco II; 1992-1997 Aerostar..."
Source: by waltersforensic.com @ http://waltersforensic.com/articles/...n/vol6-no3.htm

Miesk5 NOTE: a shop or PO could have installed this PN in other model year Broncos, see the Ford info below in the Buyer's Guide Results by FORD: Part Number: SW2103 Description: Headlight Switch, Manufacturer: Motorcraft. Years: 1990-1994 Applications: 535: 1992-1994 Bronco; 1990 Bronco II; 1990 E-150 Econoline; 1990 E-250; 1990 E-350; 1990 Escort; 1991-1994 Explorer; 1992-1994 F Super Duty; 1992-1994 F-150; 1992-1994 F-250; 1992-1994 F-350; 1990-1994 F53; 1990-1994 F59; 1990-1994 Ranger


Do a gOOgle for;

many results acorss model & model years
such as;
This is video of a 1992 Mercury Grand Marquis that had intermittent headlights. I show how to replace the switch and the melted electrical connector.

http://www.youtube.com/watch?v=99zt2_l7WTQ
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