98 dodge dakota charging issue

[87bimmer325]

98 dodge dakota had alternator and battery tested both are good, new wire from alternator to fuse box, all grounds are good. vehicle runs but when battery dies it dies, will not charge the battery or run the vehicle off alternator. is my issue in the vehicles computer, is there a fix without a new ecu ??

[silverhairdeere]

who tested altenator , and what voltage did it put out . also did you check the wiring going from altenator to battery

shd

[87bimmer325]

autozone tested it after we put a brand new one on and the condition still existed, it has one main lead goin from alternator to the fuse box then a short one from there to battery replaced teh long one the short one is good. and we baught a brand new battery

[87bimmer325]

well i thought it was the voltage regulator the whole time after the alternator tested okay, how do i go about getting the pcm ? and how much does it usually cost.

[leolkfrm]

did you put a voltmeter on the output post of the alternater? did you check for field voltage?

[87bimmer325]

voltmeter on outpost of of alternator reads 11.5-11.8 so does end at fuse box that leads to battery, both the little wires have resistence that go to the alternator , i did cut a wire on the tail light and add another for a problem with the running light this couldn't be the cause could it ran fine until this

[leolkfrm]

there should be voltage not resistance to the field terminal of the alt. if you think the wire change has something to do with it, disconnect it and check the voltage

[87bimmer325]

wire change did nothing, the outpost of the alternator had 11.5-11.8 volts tested with a actron auto analyzer, that is the post with the wire that leads to the main fuse box, there are then 2 little groudn wires on the alternator, and 2 smaller wires they both have resistence wasn't sure but read somewhere about it

[crabtruck]

Welcome to the forum 87bimmer325.
You want to be careful about the resistance/voltage thing
since you are dealing with wires that run to the pcm ($$$)

You say you've checked/tested wires,batt,alt
and you've made no mention of driving problems.
This makes me not want to rush to replace the pcm.

If you have an AT, one of the field wires also runs to tranny relay
next to fuse 3 in the power distrib center (fuse box).

Suggest you follow and inspect the wires to pcm and relay for
damage or poor routing. Sounds like you have a voltage bleed.
Since the alt is regulated by the pcm internally it's not fixable.
Think shd pointed that out already.

Suggest if no damage seen to wires, you try starting the truck
with the trans relay unplugged for just enough time to check voltage
for batt/alt.
Somebody sound off if they think this is a bad idea.

Here's a drawing showing that alt/trans relationship - see red arrow.
Click on thumbnail, then click on pic that pops up to see better.
Good luck.

[leolkfrm]

sounds good to me! it seems as the though the alt is not getting field power, almost a stupid as my bad replacement one of last year. if he disconnects the pcm wires can he do an on vehicle alt test by putting power to the field???