[ducrider]

Guys, I don't drive my 93 YJ jeep everyday, but I tried to crank it a few weeks ago after it has been sitting for about 3+ months and it would not turn over. I checked and then replaced the battery and the jeep did crank, but now the "Check Engine Light" was on. I also noticed that the voltage gauge was around 10 not in the middle at 14 which is normal. So I took it to autozone and they tested the alternator and said it was not producing anything... so took it off and replaced it... but now everything is the same, the voltage gauge is still at 10 and the CEL is still on. Could it be my voltage regulator? If so should I buy one off ebay or used? And if I do what years are compatible with my 93 YJ 4.0 Auto?

Thanks in advance
dUc

[OhioYJ]

No, you needed to check the alternator off the Jeep before replacing it. Your voltage regulator is built into the ECM, it has complete control over what the alternator does. Since the alternator did not work on the Jeep, you needed to check it off the Jeep to make sure it wasn't the wiring, this goes for any vehicle.

From my FAQ: Testing Alternators:

If you don’t have 14 volts, you need to check a few other things. Most all alternators have a wire harness going to them. One of these wires is for the field voltage, if you don’t get power to the field, your alternator won’t charge. On newer YJs and all TJs, the voltage regulator is controlled by the ECM. On these alternators there are two wires on the back, one constantly cycles between 10-12 volts to control the alternators output, while the other is a reference wire to tell the ECM how much power the alternator is putting out................................If you have power to the field, but aren’t getting 14 volts, it’s a pretty safe bet your alternator is bad.

Also a little late now, but for future reference, check out my Dodge Alternator swap.

[ducrider]

Thanks for the reply OhioYJ,

Sorry I did not go into much detail on that part but here it is:

I had the alternator checked for voltage yesterday.... In fact it is the original alternator.. I had it rebuilt by a local guy, I took it back over to him yesterday and he put it on his "Alternator Testing Machine"

"he looked over at me and said its working just fine, it could be your voltage regulator"

that is what lead me to believe it's something else going on..

thanks again

[timatoe]

As Ohio said, I'm pretty sure the regulator is built into the alt. If everything is fine coming out and the battery isn't charging, I'd take a look at your wiring.

[ducrider]

So the 1993 YJ voltage regulator is not built into the CPU?
thanks in advance

[Joe Dillard]

Have you tried pulling the codes yet by cycling the ignition key on & off in sequence?

[Joe Dillard]

You may want to try this:

http://www.jedi.com/obiwan/jeep/dtc.html

[OhioYJ]

As Ohio said, I'm pretty sure the regulator is built into the alt.

No, No, No. The voltage regulator is built into the ECM ^^Also explained in the link above I posted. There really isn't much in the alternator to wear out. You can't check the alternator in your Jeep on the vehicle, the alternator needs to be off the Jeep and be bench tested. If you have a multi meter, you can test it on the Jeep, but you aren't checking for voltage. In fact voltage doesn't tell you a whole lot.

The ECM has complete control over that alternator, there are two little wires going to the back, ^^as I posted above. Both come from the ECM, one of the little wires should constantly cycle between 10-12 volts to keep the alternator voltage inline, as the voltage drops to 13 volts the ECM should jump closer to 12 volts, as it reaches 15 volts the ECM should drop closer to 10 volts, but the ECM does it so quickly, the meter should just jump around between 10-12 volts. The other wire just tells the ECM how much power the alternator is putting out, it is tied to the charging post internally.

[OhioYJ]

If you aren't familar with using a multi-meter, take a look through my using a meter writeup:

Multi-Meter Basics

[jay-h]

Originally Posted by OhioYJ

No, No, No. The voltage regulator is built into the ECM ^^Also explained in the link above I posted. .

This is why I HATE newer cars. The computer is a single point of failure for all kinds of systems, if any part of it fails, the repair costs are stupendous (instead of 15$ for a voltage regulator).

[TSEJEEPERS]

What kind of battery are you using? The reason I ask is that if my optima red top is completely drained the alternater will not charge it without getting real hot. I have to put it on a charger overnight.

[OhioYJ]

What kind of battery are you using?

Yeah I should have mentioned that, the Jeep ECM will do funny things with a dead or bad battery. I had a WJ at the shop that the alternator was sitting at a prety solid 18 volts, when you hit the gas it spiked to 22 volts, ended up just being a bad battery. The ECM was just going nuts trying to compensate for the bad battery.

[ducrider]

I put a new battery in the jeep.

OhioYJ ...thanks a bunch on your write ups, I will check all fuses and put a volt meter on the wires leading to the alternator.

Just for reference, if I had to replace the ECU --will any ECU work from from 1989-1995 as long as its the 4.0L brain? does it matter if the ECU was auto or manual transmission?

thanks in advance

[jeepinMatt]

my alternator is just fine i took it to my shop at school and i checked using a tester, the one to put a load on the alt and ext. and it all checked out good, but my gauge is still reading only 10 or 11 and its been like this for id say 5 months or so. maybe just the gauge is out if you replaced the alt and you have no prob now, i dont even look at that gauge now

[TSEJEEPERS]

It must be a ECM from a 91-95 4.0L and which ever transmission you have. Part number for the one with manual transmission is 56027368. I just found one for mine on e bay. Good luck! It seems they are a little hard to find. Keep watching e bay. You can also send yours out to have it rebuilt at a number of places.