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Old 04-29-2019, 10:47 AM   #1
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Engine voltage fluctuations

I've got an E-250 2001 5.8 SMB.

I recently had an issue with a wonky ground off the battery neg (I've got winch wiring and a cut off and so it tends to create a poor connection over time, even though the connection seems tight: I clean the terminal, reattach, and very consistent battery voltage). But it got me to paying more attention to voltage as I drive.

I noticed that on a couple of recent occasions the range of voltage while driving was 13.2 to 13.7 or so, while as far as I can tell normal range is more like 13.5 to 14. This only happened in a couple of stints, like after a refuel. And once restarted that day or the next it was normal, including all day with about three stints driving 300+ miles. So only twice that I can recall.

Is that just the PCM or something throttling back for a reason? or a sign of a problem? It never went below 13.2, and stayed very consistent, just a lower range. My starter battery isn't the best, usually only getting to say 12.52 on a "full" charge. And I seem to have phantom drain (probably radio memory and/or remote sensing, and maybe my alarm system/remote door as well; maybe 80mA in total). But I don't think those relate.

Is this something of concern? or just normal operation?
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Old 05-02-2019, 05:07 AM   #2
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Quote:
Originally Posted by rob_gendreau View Post

Is this something of concern? or just normal operation?
Just curious how and from where are you monitoring the alternator output voltage?

If the alternator and its internal regulator are in good working order your voltage should never drop below 14 VDC with engine running, 14.3 is considered optimal. Even with all accessories powered by the starting battery and alternator on "high" that 14 volts should remain constant.

Dropping below that then returning isn't normal.
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Old 05-02-2019, 08:18 AM   #3
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Me and a friend both have 6L diesels and notice this happening. We are both monitoring our battery voltage with Edge CTS gauges and see that our volts go from 13.1 up to the occasional 14 but more like between 13.3 and 13.8 and it bounces. He has a new alternator and I have the factory 140 alternator. Strikes us as odd as my motorcycle stays at 14+ all the time when it's running.

I have new starting AGMs and so does he. Had my shop test the alternator and of course they say it is fine. Will be watching this thread to see what else comes up.
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Old 05-02-2019, 08:52 AM   #4
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Just curious how and from where are you monitoring the alternator output voltage?

If the alternator and its internal regulator are in good working order your voltage should never drop below 14 VDC with engine running, 14.3 is considered optimal. Even with all accessories powered by the starting battery and alternator on "high" that 14 volts should remain constant.

Dropping below that then returning isn't normal.
Scangauge.

And on most of my vehicles (jeep, hatchbacks, the van) the voltage regularly drops below 14v. I'd say 13.8 is probably the norm; haven't averaged it out though. Had it tested and it's within spec, even dropping into the lower 13.4ish range. Apparently the variation in one vehicle, and among vehicles, is more than I imagined. Look around on the internet and you'll see many base voltages, and some guides just speak in terms of X amount over or under no load voltage.
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Old 05-02-2019, 09:16 AM   #5
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There is a big piece of data that we are not bringing to the table, and that is the house battery, if there is one. Not so long ago I made this post about Battery Charging.

The post covers charging data from shore, solar and alternator. In the alternator run of about 4 hrs with a thirty plus min dinner break you can see the voltage levels that were captured during the run. The house battery was at 59% SOC at the start of the run.




-greg
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Old 05-02-2019, 11:39 AM   #6
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Never underestimate the number of ways in which a poor ground will drive you insane!


I'm not saying with any authority that this is your problem, but it's worth looking into, as modern vehicles have 10's of grounds all over the place, where this effects that, which effects this other thing, which makes this thing act weird sometimes...



You'd think I would finally have this lesson through my skull, but I seem to revisit this every 7yrs or so



Over the winter, I started chasing down electrical issues with my Jetta... I cleaned up ALL of the engine compartment grounds, including the large BUSS under the battery tray, took everything loose, wire brushed and sanded, used copper paste, reassembled and poof! All better now!


As I work on my '95 van, I see ground connections everywhere. I take 'em apart and clean them as I go. "The ground or return is equally as important as the +positive wire", I keep telling myself.
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Old 05-02-2019, 11:47 AM   #7
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Never underestimate the number of ways in which a poor ground will drive you insane!


I'm not saying with any authority that this is your problem, but it's worth looking into, as modern vehicles have 10's of grounds all over the place, where this effects that, which effects this other thing, which makes this thing act weird sometimes...



You'd think I would finally have this lesson through my skull, but I seem to revisit this every 7yrs or so



Over the winter, I started chasing down electrical issues with my Jetta... I cleaned up ALL of the engine compartment grounds, including the large BUSS under the battery tray, took everything loose, wire brushed and sanded, used copper paste, reassembled and poof! All better now!


As I work on my '95 van, I see ground connections everywhere. I take 'em apart and clean them as I go. "The ground or return is equally as important as the +positive wire", I keep telling myself.
I did have a poor ground problem but we corrected that before noticing the voltage fluctuations. It's now part of my regular maintenance. Sheesh, you can yank like crazy on the connections and they seem fine, but test it and it's like they are hardly connected.

And yes, I suspect that the house battery is an influence. During normal operations there are just a lot of variables, so it's really hard to replicate the "problem" here if indeed there is one.
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Old 05-12-2019, 11:20 AM   #8
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I did have a poor ground problem but we corrected that before noticing the voltage fluctuations. It's now part of my regular maintenance. Sheesh, you can yank like crazy on the connections and they seem fine, but test it and it's like they are hardly connected.

And yes, I suspect that the house battery is an influence. During normal operations there are just a lot of variables, so it's really hard to replicate the "problem" here if indeed there is one.
Be sure to check the Neg Cable at the Frame Mount location under the cross member under your Engine.. My 96 E250 Came from Ford with the Negative Cable Loose hanging on the Screw that ford uses to mount to the Cross member under the engine.. This took about 10 years to finely stop making a good enough connection for me to discover that it simply was left loose by ford .. Built on a Friday.

RE run your Negative Cables and do the Big 3 upgrade.. it will help

The Big Three wiring upgrade

A good, cost-effective improvement is to perform the "Big Three" electrical upgrade. This will vastly improve your vehicle's electrical system, allowing more current to flow easier to all components. This upgrade replaces or augments three key cables in the electrical system with 1/0 or 4 gauge wires: the battery ground to chassis wire, the chassis to engine block wire, and the alternator plus to battery plus wire. This increases your electrical system's current flow capability, ensuring a more consistent voltage under varying demand conditions.
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Old 05-13-2019, 06:25 AM   #9
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As a grounding side note, they sell "grounding kits" for most vehicles. Most people report a big difference in the way vehicles run. I believe cars turns things on by grounding to complete the circuit. There are many DIY grounding plans on the nets.
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Old 05-13-2019, 08:15 AM   #10
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As I noted I solved my grounding issue but it repeats, largely because of the need to use a post-style battery terminal. If I do switch wiring, it will be to a stud and bolt terminal. Why do post terminals still exist? for the same reason we still have cigarette lighter receptacles?
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