Voltage changes 12 to 14 volts constantly

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loganscuda

loganscuda

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I have my voltage at the battery and guage goes from 12 to 16 volts back and forth at idle it is a little better and constant at driving speed. 04 truck hemi with 05 computer. 545 tranny. replaced battery still does it.
 
My voltage regulator runs between 14.2-15.2, back and forth. What voltage regulate are you running?
 
What computer are you running? Do the hotwire computers regulate the voltage like in the lx's?
 
to computer, and it is an 05 dodge ram computer I have the same problem with the 04 computer I had on before
 
Check brushes in the alternator, but I doubt this is the problem


I would first look for voltage drop problems either or both in hot harness or in ground leg I'm not intimately familiar with these computers so I don't know where the reference ground is, so you need to refer to the diagram and find out. Essentially, there are several things that all need to be "at the same level." By this I mean within hundred's of one volt

the engine block

the body frame

the negative side of the regulator (computer ground whatever that is)

the battery negative post

On the "hot" side of things the same thing is true. There are several things that when operating need to be within a few hundredth's of one volt of one another

the battery positive post

whatever the hot supply to the computer is

the voltage sensing to the regulator if it's different from above


Because I'm not familiar with your wiring, I'm going to revert back to a typical factory Mopar harness, and ask you to visualize in your mind the "voltage path" that is involved with "let's say" a 69 Dart ----This is just an example as means of explanation........

The hot path to the regulator, which is the voltage sense, is:

From battery.....starter relay.....fuse link......through bulkhead connector.....to ammeter....through ammeter....back out ammeter......past welded harness splice......ignition switch connector.....through switch......out switch connector.....back out bulkhead connector.......to switched loads under hood (and voltage regulator)

The ground...........

From battery NEG.........to block........to ground cable........to body ground.......to regulator mount flange

Each and every one of those points mentioned is a place you can have a poor connection.

If there IS voltage drop and or poor connections in either or both the above, you can have this type of surging, and you can also have overcharging, as the voltage regulator "thinks" it is sensing low voltage.

You can also create what are known as a "ground loop" and this can also happen in the hot harness. A ground loop is a general term for a situation where a multiple ground path can cause "bad things" usually this type of "cyclic" activity. This can be caused by such things as a poor connection...........The voltage sags, the poor connection loses conductivity, and the regulator says "crap, CHARGE" and the voltage surges up, the connection "makes" across and the voltage suddenly jumps up, and it repeats, oscillates over and over.

This can also be caused by something causing some sort of TIME CONSTANT. This could be something like a STEREO AMP with a great big filter capacitor charging and discharging. Something in the added on circuitry of your EFI stuff (not familiar) might be doing this

HOW TO FIND

Check documentation for the GROUND for the ECU. Temporarily run a great big ground wire to a known ground point. (By the way, if you have a trunk mount battery with a separate ground cable, this might be a problem)

Google SINGLE POINT GROUNDING. This helps prevent ground loops.

For the "hot" side, find the main ignition / energizer feed for the computer and temporarily run a LARGE (say no 12) jumper / hot wire from there to the battery.
 
The computer regulates the voltage.
 
If you guys can use "something else" besides the computer regulator, I would. You've already pirated the computer, so to speak, as you are not using the original trans sensors and whatever else. The thing is, if something should short in the harness / alternator, it might cause problems in the computer, a very expensive possibility.
 
I think about the first thing I'd try is to run a BIG ground (even if temporary) from the ECM to the battery
 
67Dart273 said:
I think about the first thing I'd try is to run a BIG ground (even if temporary) from the ECM to the battery
Click to expand...
I did this and still no luck. I redid all my grounds and connections and still get the same result. Using a volt meter at the battery when running its bounces from 13 to14.8..
 
I'm just about out of ideas, other than to abandon the regulator in the computer (that is what you are using?) and wire it up to a 70's Mopar unit.

a few things I would do.

With it running, and in a situation to exhibit the probem, "rig" a big jumper so that you can get your voltmeter hooked directly to the battery ground clamp. Then probe the ground point at the ECU. Try this with various loads, headlights, etc. ANY voltage reading means it's not really grounded

Double triple check your ECU wiring to be sure there are no factory ECU ground wires left out

Finally, "rig" a big jumper to "hot wire" the ECU direct to battery for switched power. You'll have to refer to your ECU wiring, there may be more than one, IE "main" power and ignition switched. That is, go direct with a nice big jumper direct from battery and eliminate all harness and connections in between.

Unfortunately I don't really have experience with these new systems, so I'm not familiar with all the various ECU "tricks"
 
I have found using a sealed beam headlight is the best way to test circuits. It puts that circuit your testing under a load.
Get a two wire headlight and run one wire to the battery positive and the other with a t-pin and check grounds right at the computer. If the ground is good you will have a nice bright light.
Do the same with lead on the ground post of the battery and check your hot wires right at the computer.
Good bright light = everything ok.
Weak-dim light = bad wire or connection
This will make sure the hot and ground circuits are good.
 
blown71duster said:
I have found using a sealed beam headlight is the best way to test circuits. It puts that circuit your testing under a load.
Get a two wire headlight and run one wire to the battery positive and the other with a t-pin and check grounds right at the computer. If the ground is good you will have a nice bright light.
Do the same with lead on the ground post of the battery and check your hot wires right at the computer.
Good bright light = everything ok.
Weak-dim light = bad wire or connection
This will make sure the hot and ground circuits are good.
Click to expand...

Sorry this is NOT the way to check grounding. This thread might just be an example of WHY it won't show what you want.

Picture in your mind a conventional Mopar regulator, and visualize that there is poor grounding between the regulator and the battery. Your headlight "brightness test" won't show up a few ohms difference

Perhaps a better example is the typical voltage drop in the battery to ignition harness in many of these cars. 1/2 a volt difference from battery to regulator (ignition) will still allow the car to "appear" to work just fine, except-------that this ADDS 1/2 volt to the charging voltage at the battery!!!

There is only one way to see this, only ONE. And that is by voltage drop, looking for a few tenths of a volt difference UNDER LOAD.

This ladies and gentlemen, is known as Ohm's Law.
 
67Dart273 said:
Sorry this is NOT the way to check grounding. This thread might just be an example of WHY it won't show what you want.

.
Click to expand...

This is the best way I have found of checking power and grounds. You can have a bad wire or with pinhole in the insulation and have a couple of good strands of wire left and pass an ohm test but it wont allow enough current to power the light.
I read that tip on IATN network which is a site for techs all over the world , Makes for a low budget way to check using a high amperage load to check wire integrity.
Here is a post from IATN on a Chrysler charging problem


.. & was going to suggest high resistance/ bad connection my self.. If all of that checks out ? there are some posts in the arcives that tell you how to wire in an old style voltage regulator, so you don't have to spend the $$ for a new computer.. Would hate to hear you replaced the computer & the problem was NOT Fixed !! But it happens all the time ;>{ That is where checking the wire/connectors resistance IS Important !! & some of the ground locations are in redicolus spots on these Dodges... IF you have a pinout of the PCM {?} then you could unplug the PCM connector & using a SEPERATE battery attach the + wire to the DISCONNECTED ground OF THE VEHICLE BATTERY & plug in a headlight bulb { High or low beam NOT Both } to the sense wire of the Disconnected PCM connector & ground the headlight back to the Seperate battery.. IF the headlight bulb lights Brightly {?} then you have proven the ground side of this circuit is capable of flowing 10 amps & the connections are tight.. The same Can be done on the positive side of the circuit, but EVERYTHING ELSE MUST BE DISCONNECTED !! There Is NO Check in the mail !! Be CAREFULL !! Hope this Helps ;>? K.P.
 
blown71duster said:
You can have a bad wire or with pinhole in the insulation and have a couple of good strands of wire left and pass an ohm test but it wont allow enough current to power the light.
.
Click to expand...

Sorry, again. This is horse ****.

This is WHY as I said you check these UNDER LOAD. A "2 strands left" wire UNDER LOAD will NOT flow the current it is supposed to flow and STILL MAINTAIN "no" voltage drop.

Ya know I really effing get TIRED of trying to teach ohms law basics to some of you guys. Go learn some of it. There are other laws that go with Ohm's Law, and "Kirchoff's Law" is just one. Google it. They are real, actual scientific "laws" of "how **** works" They were invented by really old guys one hell of a long time ago, and guess what? It all still holds true today. The DIFFERENCE today, is, we now have easy, inexpensive access to VERY accurate digital voltmeters, which were not available when I was a "kid," and certainly not when these laws were written

A light bulb will NOT show up a few tenths of a volt drop. There is ONLY one way, short of expensive laboratory equipment to test fractions of an ohm resistance, and that is using a good voltmeter with the circuit UNDER LOAD
 
Just trying to help out and this is a quick and easy way to check and verify good power and grounds under load to the ecm , which it must have. A lot of guys don't have a good dvom .

Beyond that it may just be a nature of the beast with a modern ecm in these older vehicles. They rely on inputs such as battery temperature and you really would need a scan tool to check to make sure everything input wise is correct and also see if there is any codes related to the charging system.
I would contact Hotwire and see if this is common for this setup.
 
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