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2000 Dodge Dakota
Truck running fine all summer. Have 2 vehicles so not unusual to sit for 2 or 3 weeks without running. I have a plow for the truck for winter and did not appear to have any problems until I used the plow for the first time this winter. (ran into same problems last year and spend numerous hours and money to gain no positive solution)

The truck battery (brand new - high capacity) appears to drain itself. Plow is currently disconnected by the way. Charged the battery - truck started and ran fine. Has sat for 2 weeks now, won't start. Charged the battery again - truck starts, but it will not stay running. As soon as I take my foot off the gas, the engine dies.

Before I spend $'s towing and whatever else they want to replace, does anyone have any suggestions? Is it possible the truck thinks the plow is still hooked up and drawing power some how? Is it possible the computer needs to be reset? Is there a reset I can do myself? Any suggestions would be greatly appreciated
 

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2000 Dodge Dakota
Truck running fine all summer. I have a plow for the truck for winter and did not appear to have any problems until I used the plow for the first time this winter. (ran into same problems last year and spend numerous hours and money to gain no positive solution).
What investigation did you do to it last year?

The truck battery (brand new - high capacity) appears to drain itself. Plow is currently disconnected by the way. Charged the battery - truck started and ran fine. Has sat for 2 weeks now, won't start. Charged the battery again - truck starts, but it will not stay running. As soon as I take my foot off the gas, the engine dies.
That is not a good sign. I won't go into starting circuit details as
the truck seems to start fine, but there appears to be an unusual drain
on the new battery, discharging it faster.

If the battery is fully charged and the truck starts but dies..you may have a charging problem.

The way it works on the Dakota is:

There is a fusible 140 amp link in the PDC that connects the battery + post
to the alternator stator 3 phase rectifier.

By 3 phase, I mean there are 3 separate windings in the alternator (120 degrees apart electrically speaking... based on a 360 degree rotation of the rotor) that generate ac voltage when the engine is running.

The battery being DC, requires a rectified ac voltage (DC voltage) to charge it,
hence the 3 phase power diode bridge inside the alternator.

There are 6 diodes in the alternator diode bridge (two diodes per winding),
(windings are arranged in the "Y" configuration with a common connection
between all 3... (in the middle of the "Y" that goes to ground through two
diodes as well.
These are press-in 100 amp power diodes, by the way, because of the huge currents involved when charging, if the battery is discharged.

Any leakage (ie: short or low resistance in one or more of the diodes)
will cause a leakage current to ground and over time could drain the
battery.

The exciter field current (in the alternator rotor winding, turned by the serpentine belt pulley), is supplied by the PCM, which monitors the charging volts across the battery..typically 13.8 to 14.2 volts across the battery posts when the engine is running or more than just a 600rpm idle.

So in effect the PCM is the voltage regulator for the alternator.

Before I spend $'s towing and whatever else they want to replace, does anyone have any suggestions? Is it possible the truck thinks the plow is still hooked up and drawing power some how? Is it possible the computer needs to be reset? Is there a reset I can do myself? Any suggestions would be greatly appreciated
No, a computer (PCM) reset won't fix this problem in my (electrical engineering)
opinion.

1.You need to get a Digital voltmeter and check what the charging voltage
is across the battery. If it is more than 12.6 volts but less than 13.8 vdc
on a fast idle (1000 rpm) it might be time to maybe replace the generator (alternator), especially if the battery has been replaced.

I will assume that when you mentioned "new battery" , the new battery is capable of taking a charge here?

2. Disconnect the positive cable on the battery and install an ammeter
to see what the drain is. If you can't find an ammeter (which measures amps only).. most Digital voltmeters have at least a fused 10amp shunt with a separate plug to test current. That may be sufficient to find a short with a draw
under 10amps...which will discharge a fully charged battery overnight.

Also, as a crude test tool, you can also use a 12v automotive signal light light bulb with the solder terminal touching the + battery post.. and the battery cable
touching the side of the bulb (1157 or equivalent).

The bulb may have a slight glow, as the "keep alive" current needed by the PCM requires a steady draw off the battery, but it should be less than half an amp at best.

IF the bulb is glowing brightly..you have either some kind of "low resistance"short to ground or something is drawing power when it
shouldn't be.

To trouble shoot the problem..solder a couple of pigtails
to a 1157 type single contact bulb and then
a) connect (wrap) a sufficiently long bare end (or use a small metal screw) to the TOP of the battery + post.

b) Connect the other lightbulb pigtail to the battery positive cable.

If the light bulb is glowing brightly, start investigating any wires (snow plow wire harness etc) or the alternator 'shorted diode" condition above, that may be causing the bulb to glow brightly..

..until you find the wire(s) or disconnect the source of the short )
which will be the 140amp fusible link in PDC, in case of the generator, that will return the bulb back to a just a barely perceptible red glow on the test bulb filament.
 

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No Idle

My 1998 Dakota 3.9L would start but not run. I came to this user group and found the information I needed. The idle air controller on the throttle body was just about gunked in place. I removed the three sensors connected to the throttle body, removed the throttle cable, and the cruise control cable. Once I removed the throttle body, I noticed that the inside was just about black with gunk and the orifice where the idle air control module plugs in was almost completely clogged.

Twenty minutes of cleaning with solvent and the truck runs fine. THANKS folks for all the good information on this site. Also, be VERY careful when taking the cruise control cable off. The connector on the end of the cruise control cable is plastic and is very brittle in cold weather, and it doesn't pop off like the throttle cable, it has to be slid off. If it is very cold outside, I would suggest holding the connector in your hand for a few moments before trying to slide it off.
 
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