greengoblin

97 xj 4.0 with 90 amp alt. its a year old and the last few days the alt has been reading 14.39volts at an idol. and if reved up to 2000 rpm it jumps to 15.28. is this normal? or is the regulator going bad? i dont want over charging to happen

freegdr

how olds the battery

greengoblin

its a year old. and i checked the batt voltage with the xj off. it was at 12.99 volts.

freegdr

check all connections on alt and battery

99exjay

It sounds to me like the regulator is going bad.

greengoblin

that sucks the alt. is les than 2 years old

freegdr

not a 100 percent sure but i think the regulator is in the computer your alt is working its over charging

greengoblin

cant be the cable comes from the alt. to the batt. so it must be internal i would think

mentalbreakdown00

Over charging is usually from bad grounds, or a faulty reg, and yes the reg is in the ECU.

greengoblin

dam!!!!!!!!!!!!!!! the ecu. about 2 months ago i replaces all the pos. and neg. cable to the starter,the block,firewall.fender and added a ground to frame by swaybar. all have to check them then and if not ill have to find a ecu then. if thats what it is.

mentalbreakdown00

check all connections for tightness and cleanliness, most of the time thats what it is

99exjay

I am not trying to disagree, but are you sure the regulator is in the ecu? Just an alternator will put out AC, there should be diodes built in to the alternator to covert it to DC and a regulator to control the output voltage when the current is increased due to higher engine RPM. My understanding of the regulator is it is some type of variable resistor in series with the coils on the alternator to lower (or raise) the amount of current flowing through the coils to increase or decrease the voltage output. If the alternator has a DC output how is the regulator not in the alternator? Perhaps the logic circuitry that controls the variable resistor is in the ECU?

Again not trying to disagree, I am not very familiary with vehicle charging systems.

Edit: The more I think about it the current supplied to the rotor could be coming from the ECU and controlled in the ECU, meaning the regulator is in the ECU. I will have to check this out when I get home tomorrow.

greengoblin

ok im going to take all the grounds off and clean everything with a wire wheel. and change any bad connectors tomarrow after work

greengoblin

will a ecu out of a 96xj work in my 97?

greengoblin

ok cleaned all the grounds and still high voltage so i guess i start looking for a ecu. well that sucks