97 zj 4.0 external voltage regulator installation - JeepForum.com
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post #1 of 24 Old 07-14-2021, 10:17 PM Thread Starter
Zjeep97
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97 zj 4.0 external voltage regulator installation

Got a 97 jeep zj - week ago I had a check engine light pop up code 12 and 24 . Replaced the TPS and upgraded to a 136amp Alternator from the factory 90amp. After that the light turned off 2 day later its back on this time code 12 and 23. Did some test on the alternator and battery. Voltage at idle....13.61.......voltage with a load ....13.49.....battery with key off 12.92. The voltage gage in the dash has allways to me been on the low side ( check thumbnail)

Over the years I've had to replace more then a few batteries, Alternator. Replaced the main computer 2 times. With that I've never had any other problems ect and drove around with no issues.

I'm thinking my voltage regulator is bad and that I may have to install a external voltage regulator. Any one in this forum have any experience with this setup I've watched a few videos on YouTube and a few Google searches but each one was different from each other.

Any help would be greatly appreciated.

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post #2 of 24 Old 07-14-2021, 11:12 PM
jtec
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was this no help?

https://www.jeepforum.com/forum/f20/...97-zj-4437821/

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 24 Old 07-15-2021, 07:06 AM Thread Starter
Zjeep97
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Got it back up and running then back to the same issue looks like its was not the fix a mechanic friend told me I may need to replace the computer or try this external fix..... ect
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post #4 of 24 Old 07-15-2021, 07:54 AM
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what issue is back?

those codes should not cause a battery charging issue. TPS and IAT
You posted voltages at idle - the system is tested at @2500rpm, I use 1500rpm, to ck output.

Jeep is STOCK no added modified changed electrical? Yes I realize alt is upgraded to @130amp.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #5 of 24 Old 07-15-2021, 08:16 AM Thread Starter
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I've upgraded the the battery cables Grounds ect to a 4 gage from the factory size installed an 150amp fuse inline to the battery. Other then that no other mods. On the( Code 12*is set when the battery has been disconnected and the computer (ECU) has been reset. The power limited light will not light and limp mode does not apply. This*code*shows up when power to the computer has been interrupted as when the computer has been reset by disconnecting the battery) was some kinda of changing system issue. And I've run them mods for years and no problems till now. Was driving down the highway during a bad storm was thinking water may have gotten somewhere and messed up the alternator.
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post #6 of 24 Old 07-15-2021, 09:05 AM
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I am seeing this - code 12 - as a BATTERY issue not the alternator.

The alt codes would be OBDII IIRC p0622. p1594, p1684 BUT we should check that - memory is OLD.

I always wonder how the external regulators operate without setting a DTC. And having the CEL and battery light on. Again I don't think your alt/charging system is bad.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #7 of 24 Old 07-15-2021, 09:12 AM
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Quote:
Originally Posted by jtec View Post
I always wonder how the external regulators operate without setting a DTC. And having the CEL and battery light on. Again I don't think your alt/charging system is bad.
You put in a resistor that spoofs it into thinking the Alt is still in circuit on the PCM.
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post #8 of 24 Old 07-15-2021, 10:08 AM
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Wyo that is interesting,
Am I right- the 2 OEM field wires are removed*, a resistor installed, BUT when the PCM commands field, the voltage on driver side would not change. IDK - but am glad there is a solution I will look for more info.

*Field is then switched by external regulator?
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 24 Old 07-15-2021, 01:04 PM Thread Starter
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I dont have a code reader just what shows up on my dash with 5 key cycles. The battery is a few months old odyssey.
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post #10 of 24 Old 07-15-2021, 01:57 PM
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Quote:
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Wyo that is interesting,
Am I right- the 2 OEM field wires are removed*, a resistor installed, BUT when the PCM commands field, the voltage on driver side would not change. IDK - but am glad there is a solution I will look for more info.

*Field is then switched by external regulator?
Yup, external regulator controls the field. And a power resistor is used to fool the ECU into thinking that their is a load on the regulator driver. Similar to what is needed when replacing halogen headlights to LEDs.

Here is a kit that has everything included: https://store.alternatorparts.com/hd...ement-kit.aspx

These kits will produce a much nicer 14+ volts which is nice if you do a bunch of winching in the summer months because of how our ZJs reduce alternator output based on battery temps.
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post #11 of 24 Old 07-15-2021, 02:08 PM
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thanks for the info - I will read later.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 24 Old 07-19-2021, 08:45 AM Thread Starter
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So I went through all my charging wire system cleaned each terminals. So far has now no problems. I did notice I did not have a ground wire from the head to the firewall. On the zj should there be one or is it located somewhere else?
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post #13 of 24 Old 07-19-2021, 09:16 AM
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I just replaced the head on my '98 GCL and there is no wire from the head to the fire wall. There is off course a ground on the block.
Never rule out a new battery causing problems. How is there electrolyte level in the cells?

With every thing turned off, how much current is the Jeep drawing from the battery? You should only see a very small miliamp draw from the clock in the radio or the like.
If you see anything over one amp, you need to start pulling fuses and find the circuit causing problems.
Corroded wires / connectors / sensors.
I would not use the dashboard voltage gauge as a diagnostic tool,only an external meter for any troubleshooting.
As for the voltage regulator, see what the voltage and current draw is with the engine idling and nothing on,rev the engine as you have done for that reading.

Now turn on everything at idle and revving the engine, you should see the voltage drop and then kick up to compensate for the load on the battery. This should happen almost instantly. If you see this,your regulator is working. If it the voltage stays low,you have a problem in the regulation circuit.
Many of the parts stores have a free code check. I would do that to see if a code is not being displayed on the dashboard.
Saying the computer is at fault without proving it is a waste of time and money.
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post #14 of 24 Old 07-20-2021, 12:33 PM Thread Starter
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So checked the current draw on the battery.. at first it read 0.21ma and after a few minutes it dropped to 0.04ma....... so I think im good there now on the regulator...... jeep off at battery 13.09v at idle 13.77v and at idle under load 13.60v.
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post #15 of 24 Old 07-22-2021, 09:45 AM
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FWIW the code 12 is not particularly diagnostic and somewhat notorious for hanging around. IMS officially it takes something like 50 start cycles to clear. I think in the entire 14 years I owned my 93 the 12 only wasn't present once.
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