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#2407334 - 11/22/17 10:17 AM Fixed! Over Charging Problem 68 Dodge Truck
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
Ok, I've been reading heavily everywhere to diagnose this.

Truck cranks forever & sputters when letting off the key. For the last 6 months it was starting often when letting off the key. I've read about voltage drop through firewall plug and bad ignition switches. I've improved the problem by either replacing or fiddling with ECU harness (converted to Mopar electronic ignition). That fix doesn't last long and it happens again.

I have a Volt meter in place of AMP gauge inside the truck and it is now reading at 10- while idling and getting close to 12 with rev. Previously, it was 11.5 @ idle and almost 14 with rev.

I know there are a lot of variables, but is there a diagram somewhere that shows me acceptable voltage readings to the corresponding point under the hood? I know there is expected drop for each component but trying to figure out what readings I "should" be getting.....

Thank you in advance!


Edited by wally426ci (12/16/17 02:12 PM)

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#2407346 - 11/22/17 10:43 AM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Supercuda Offline
I Live Here

Registered: 09/04/07
Posts: 13220
In order to know your voltage drop you have to know what is coming out of hte alternator.

10V at idle with 12V revved up is BAD.

11.5v at idle with 14 revved is also bad.

Since we have no idea where you voltmeter is actually tied into the system it's hard to say what it's reading. If you simply bolted the two ammeter connections together and used that point as the freed for the voltmeter then you should be reading alternator out put and if it's that low you have serious issues.

We may as well start at the beginning ...

What is the reading at the battery positive - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

What is the reading at the alternator stud - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

What is the reading at the coil positive - (use engine block for ground)

engine off -
engine at idle -
engine at 2500 rpm -

Once we have these we can go from there

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#2407347 - 11/22/17 10:43 AM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
469runner Online   content
super stock

Registered: 01/07/04
Posts: 1078
Loc: North Carolina
Check your Ballast resister.

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#2407348 - 11/22/17 10:44 AM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Andrewh Online   content
master

Registered: 02/17/03
Posts: 7765
There really isn't an acceptible amount. Variances of .1 or so are expected.
But it sounds like you aren't charging at all.

It also sounds like you have done some modifications so a generic 68 diagram might not help.

The key is voltage based on the ground.
That is to say, where you are tapping the ground for will affect the voltage you see at whatever line you are checking.
So it matters what the ground is for the item that needs to get the voltage.

So if I test the voltage reg for the charging system, I touch the sensing line(which is exposed on a factory 68 but not on the 71 and up) for the positive and the case of the voltage reg for the ground.

IF the case is not properly grounded the voltage will differ if I used the battery for ground instead.
Both of the actual postive voltage provided and the ground to the voltage reg will change what the voltage reg shows.

All of these readings should be compared to the battery directly using the battery pos and neg posts.

Also be careful on using the bolt or screw holding a wire in place instead of the actual wire as the touch point, as this too can give you a false reading depending on how good the connector is on that wire.

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#2407349 - 11/22/17 10:44 AM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: 469runner]
Supercuda Offline
I Live Here

Registered: 09/04/07
Posts: 13220
Originally Posted By 469runner
Check your Ballast resister.


Ignore this.

The ballast resistor will NOT have any affect on system voltage, which is very low.

Nor is it used in START. It is bypassed with the key in START and the fact that it will sometimes start when the key is released shows it is good.

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#2407470 - 11/22/17 02:41 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
None2Slow Offline
mopar

Registered: 02/27/07
Posts: 598
Loc: Nampa, ID
What about the ignition switch? You could have bad or dirty contacts in there that are not allowing you to get a good connection when starting.

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#2407485 - 11/22/17 02:59 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
Thanks ya'll! I will report back.

I did a clean Madd rewire all the way to gauges so solid wire where amp was. Voltmeter feeding from full volt side of cluster

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#2407516 - 11/22/17 04:04 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
RapidRobert Online   content
Circle Track

Registered: 11/20/03
Posts: 33675
Loc: Lincoln Nebraska
Quote:
Truck cranks forever & sputters when letting off the key. I've improved the problem by either replacing or fiddling with ECU harness (converted to Mopar electronic ignition).
4 pin orange box I am assuming. I would jump 12V from the battery positive post to the blue yellow ECU terminal and to the coil positive primary terminal & seperately (on the ground side) from the ECU base to ground then crank it & see if it starts several times in a row & only let it run for several seconds if/when it does start to confirm or elim the coil/ECU are good tho they can be OK when cold then act up when hot but you did say this was an initial in the morning starting problem. then as said check voltage drops at the coil/ECU when cranking OR just start cleaning ALL terminals/connections especially the bulkhead & ign sw.
_________________________
live every 24 hour block of time like it's your last day on earth

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#2407699 - 11/22/17 11:25 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
Thanks Robert - hoping you would chime in to reason me through another issue. I'll get you a plane ticket one of these days.

Battery was 12.5 across terminals. I got 11.85 tops at the positive alternator stud but I am idling super low?

I did replace the ignition switch with new for kicks and it started easier twice in a row. Voltage gauge inside still reading low.

I'll get some solid readings tomorrow and report back.

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#2407700 - 11/22/17 11:36 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
RapidRobert Online   content
Circle Track

Registered: 11/20/03
Posts: 33675
Loc: Lincoln Nebraska
Thank you for the kind words & I could use a vacation but the thought of the airport delays would probably make me want to stay put. for the charging rate I would confirm that the battery is full charged by slo charging it with a charger to full charged then put it on a fast idle & see what you get at the alt & at the batt terminals. I'm wondering if this is a charging rate or a voltage drop (connections/terminals) or a part (coil/ECU/switch) issue. The battery could be sulphated (least likely) but a possible potential. We're getting there.
_________________________
live every 24 hour block of time like it's your last day on earth

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#2407705 - 11/22/17 11:52 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: RapidRobert]
Pacnorthcuda Offline
I Live Here

Registered: 11/19/07
Posts: 19006
Loc: Kirkland, Washington
Originally Posted By RapidRobert
Quote:
Truck cranks forever & sputters when letting off the key. I've improved the problem by either replacing or fiddling with ECU harness (converted to Mopar electronic ignition).
4 pin orange box I am assuming. I would jump 12V from the battery positive post to the blue yellow ECU terminal and to the coil positive primary terminal & seperately (on the ground side) from the ECU base to ground then crank it & see if it starts several times in a row & only let it run for several seconds if/when it does start to confirm or elim the coil/ECU are good tho they can be OK when cold then act up when hot but you did say this was an initial in the morning starting problem. then as said check voltage drops at the coil/ECU when cranking OR just start cleaning ALL terminals/connections especially the bulkhead & ign sw.


Wally,
As FastBob states above, check your bulkhead connections. Your comment "sputters when letting of the key" is a classic indicator that the STARTING circuit to the ignition has failed. Not uncommon.

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#2407829 - 11/23/17 10:38 AM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
dvw Offline
master

Registered: 03/16/06
Posts: 6990
Loc: MI, usa
If It wont fire until the key is released the blue/yellow circuit to the ECU is dead during crank. Where? It depends if how it was wired when installed. Where was the wire attached to the ignition on circuit? Be aware that Mopar has 2 ignition circuits. Ignition 1, is hot in run but not crank (I believe red on your truck). Ignition 2 is hot in crank, but not run (I believe pink on your truck). The best way to find voltage drop? Connect a voltmeter hot to hot (positive side drop) or ground to ground (negative side drop). In your case battery positive post to the Blue/yellow wire. Crank the engine. By all rights the voltmeter should read zero. It won't. What ever reading you see is how much voltage is lost between the circuit testing point and the battery positive post. Don't be surprised to see readings of .5-1.0 volts. More than that is an issue. Start at the battery terminal and work your way down the the circuit. Do this test while the circuit is loaded. Such as while cranking, while running or with what ever component you want to test is switched on.
Doug

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#2408718 - 11/25/17 01:42 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
Ok report #1

Battery fully charged

Voltage

Batt positive
engine off 12.68
650 rpm idle 12.26
2500 rpm 15.5

Alt stud
Engine off 12.67
650 idle 12.25
2500 rpm 15.5

Coil positive
Engine off 0.03
650 idle 10.3
2500 rpm 11.6

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#2408725 - 11/25/17 02:07 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Andrewh Online   content
master

Registered: 02/17/03
Posts: 7765
that 15.5 is too high.
what did your voltage reg read at the sensing line?

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#2408735 - 11/25/17 02:42 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Supercuda Offline
I Live Here

Registered: 09/04/07
Posts: 13220
As Andrew said, 15.5 is probably too high, your idle is too low. Your coil voltages look ok and where you have checked I do not see a voltage drop issue.

I would say voltage drop to the voltage regulator on the sense side needs looked at, usually it's a blue wire but it is the switched 12V feed to the VR. Measure that to engine block and it should be the same as the battery + terminal or alternator output stud voltages, if not you have an issue if so it's probably the regulator.

In 68 you should still have the single field terminal alternator with the mechanical regulator system, unless it has been changed.

If you are still running the mechanical voltage regulator instead of the later electronic version of it (not to be confused with the 70 and up regulator) you can adjust turn on and turn off voltages. To tell if it's the mechanical regulator look at the bottom, if it has a couple wire wound resistors it's the mechanical one. The FSM has adjusting procedures in it.

No truck FSM's, but the 68/69 pass car ones have the relevant info in them

http://www.mymopar.com/index.php?pid=109

I would think about converting to the newer charging system

http://www.mymopar.com/index.php?pid=78

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#2408747 - 11/25/17 03:53 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
I have not probed the regulator points. I did swap the regulator for no change. I then decided to swap another alternator in. That changed the volt ratings inside the truck and it now pulses by a half an amp or so..

See my youtube upload https://youtu.be/6DkWHOLzsxk

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#2408748 - 11/25/17 03:57 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Supercuda Offline
I Live Here

Registered: 09/04/07
Posts: 13220
that is what a mechanical regulator looks like when it's doing it's thing.

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#2408750 - 11/25/17 04:03 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Andrewh Online   content
master

Registered: 02/17/03
Posts: 7765
you still need to verify sensing voltage, and as said before use the case as your ground point.

I expect you will find at least 1 volt drop causing your higher charging voltage.

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#2408751 - 11/25/17 04:03 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
wally426ci Offline
master

Registered: 07/26/07
Posts: 2516
Loc: Maryland
Actually, i have it set up to newer square back with mopar electronic ign

Are you thinking i should leave it and see how it goes?

My analyzer ws flashing bad alt brushes on the previous alt...

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#2408800 - 11/25/17 06:24 PM Re: Finding the Voltage drop 68 Dodge Truck issue [Re: wally426ci]
Supercuda Offline
I Live Here

Registered: 09/04/07
Posts: 13220
If you have the newer setup and it's doing that you have a problem.

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