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High Voltage Hemi

Sixpactogo

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I have installed a 6.1 Hemi in my 68 Charger. The thing starts and runs fine except for an excessive charging problem. I have correct battery voltage everywhere I test in the key off and key on mode. I have 7 grounds on the vehicle that all test O-.3 ohms. The battery voltage is within .2 volts. When I start the car, it almost pegs my in dash volt meter (15.8 volts) With my digital volt meter, I read 15.8 volts at idle and 16.1 @ 2500 rpm. Everyone I talk to has a different spin on the issue from:
1.That is normal.
2. You have a bad ground.
3. You have a bad connection
4. You have a bad ignition switch
5. Your problem is in your wiring somewhere.

Almost every answer except what I believe it is. I think it is in the computer program since the computer regulates the voltage internally.
I had my buddy check the system with his scan tool and it says (desired voltage is 15.3)
I think the desired voltage or regulated voltage needs to be dropped to a more acceptable value since I believe the 15.8 - 16.1 volts will cook my battery.
Anyone out there run into this issue?
 
Have the alt. load tested. It's either the alt. or the computer.
 
I'm in agreement with you.
I have load tested the Alternator, replaced it with a different one. Replaced the ignition switch, tried a different battery, jumped through the hoops that Chris at Hotwire told me to do with replacing the start circuit from the ignition switch to a push button. All with the same results. Bouchillon and Hotwire gurus all say it is not in the computer. I don't know where else it can be.
The computer is doing what it is supposed to do but to me, the problem lies in the regulated voltage that the computer wants to see. I think they need to change the values in the computer to something lower than the 15.3 desired volts. Probably something like 13.8 or 14.0 volts but they disagree. I am sure it will get figured out somehow but was wondering if anyone else had the same issue.
I am considering swapping the field wires feeding the Alternator but was told it won't matter.
Just don't know what else to try.
 
If the voltage is low that the voltage reg is looking at it will over charge
or wiring is wrong


Test wiring inputs from pos battery to inputs perfect should be zero volts but should be less the .5 volts
 
I agree with that also. I have tested the computer plug-in values as well. Connector 1 Pin 29 should have constant battery voltage and pins 11 & 12 should have battery voltage with key on. All 3 show 12.5 V (same as battery) with no voltage drop. Pins 9 & 18 are ground. Both show .2 ohms.
I see no way for the computer to see a voltage other than what is at those pins unless the values inside the computer are wrong.
 
Are you using a Chrysler PCM and alternator? Stock PCM's control the field on the alternator. Chrysler alternators are internally grounded. You have two wires on the plug in the alt. These are the field control. One is power and the other is ground provide by the PCM. What is your voltage on the hot wire with the engine running? The other is a PWM ground. This controls the output. If you full field the alternator, this becomes a constant ground. So the hot is essentially a "sense" circuit so the PCM knows the voltage and the ground makes the alternator output. Your meter will "average" the voltage on the ground with the car running. What is the voltage?
 
OK, Here is what is happening. I have the Chrysler PCM and stock 6.1 alternator. The PCM is from Bouchillon Performace and has been re flashed by their computer guru to work with my set up. After much ado about the PCM set up, I finally convinced them that the problem is not in my wiring but in the PCM. I sent it back to them and they changed the voltage value in the PCM by lowering it one volt. That is why the scanner tool now reads 12.5 instead of the real battery voltage of 13.5 volts. I have been trying to convince them that they lowered the wrong voltage and should have dropped the desired voltage from 15.1 to 14 volts. Before I sent the PCM back to them, I read actual battery voltage 13.5v at the field wires at the alternator. Now, I read 12.5v at the field wires. I have swapped the field wires because I too thought I was full fielding the alternator but it made no difference. I am now in the process of sending the PCM back to Bouchillon in hopes that they will be able to change the battery voltage back up the one volt and lower the desired voltage by at least a volt. To me, a desired voltage of 15.1 is too high and will cook the battery in short order. Here are a couple of scan screens showing what the computer sees. I am still confused why the desired voltage is 15.1 and when I test voltage at the battery with the engine running, I am reading 15.8 at idle and 16.1 at 2500 rpm on my Fluke meter.
100_7547.jpg100_7548.jpg
 
I am still confused why the desired voltage is 15.1 and when I test voltage at the battery with the engine running, I am reading 15.8 at idle and 16.1 at 2500 rpm on my Fluke meter.

image.tiff



Here is the connector. 1 is field control and should be in PCM connector C2-19. 2 is the voltage sense, and goes to C1-24. Just verify they are not reversed. You need to check voltage at C1-24 at the PCM (back probe) and verify it it the same as what the scan tool displays. As long as the PCM is requesting a desired voltage that high, it is going to make the alternator try and produce it. Most of the LX cars I work on usually requesting a desired voltage of 13.6-14.4. Never seen one asking for that much.

- - - Updated - - -

Can't get the connector to show, so just snapped a pic.


 
Thank you! I wish I would have had that info before I sent my PCM back to Bouchillon. I did know the plug configuration and checked the #1 wire on the plug (green) and it was on C2-19. The black wire on #2 went to ground. When I get it back, I will check at C1-24.
The 13.6 - 14.4 volts for desired volts is what I expected to see on the scan tool. If Bouchillon can't lower the desired volts to that threshold, I guess they need to replace it.
Thanks again. I have been chasing this issue for 2 months.
 
Thank you! I wish I would have had that info before I sent my PCM back to Bouchillon. I did know the plug configuration and checked the #1 wire on the plug (green) and it was on C2-19. The black wire on #2 went to ground. When I get it back, I will check at C1-24.
The 13.6 - 14.4 volts for desired volts is what I expected to see on the scan tool. If Bouchillon can't lower the desired volts to that threshold, I guess they need to replace it.
Thanks again. I have been chasing this issue for 2 months.

Sure. If #2 went to ground, you had NO voltage sense, which I'm guessing is your problem!
 
I do have voltage sensing at the plug. I read battery voltage between #1 & #2 with the engine running. I did not check it to ground but I got a diagram from Hotwire. It showed the green wire on #1 going to C2-19 and the black wire on #2 referenced to engine ground. I knew #1 went to C2-19. I verified the green wire was on C2-19. They didn't give me a pin # as to where #2 wire went. Only to engine ground. I have high hopes that Bouchillion will be able to lower the desired voltage threshold to under 14.4 volts in my PCM. Otherwise I will be after them to replace it. Thanks again.
 
Problem finally solved. I sent the PCM back to Bouchillon and they were able to fix the voltage issue. I got it back today and now my voltage is running where it should 14.3V
Gotta love it.
 
Glad to hear that. I was going to say that on the Mopar controllers the outside temp also will change the target voltage. With the scanner I would always look at the target voltage as thats what the PCM is looking for and will adjust the field to see that voltage. Also on some newer years (I forgot what years as I retired in 2011) the PCM would controll the field input and ground as its easy to tell as both field wires go to the PCM on that type. But very glad to hear you got it fixed as you seem to know the system very well since you knew to make sure the 12 volt hot feeds to the PCM are critical since the PCM uses the 12 volt feeds to monitor charging volts. And you knew to check the grounds real good. Ron
 
I appreciate all of the responses on this issue. I don't know what the Motorola guy did to fix the voltage problem. I was not aware that PCM monitors battery temperature. I saw in the scanner window that my battery temp was -83F. I disregarded that info as there is no sensor to monitor the battery temp. Maybe that is where the glitch was. I also saw the scanner tool said my AC Hi side was 483 psi when there is no sensor for that either. I have no idea how the PCM gets data where none exists. Maybe I should just stick with the vintage stuff where you only need spark and gas to run.
 
Many PCM's now have a temp sensor unit in the PCM but many over the years also had a seperate battery tenp sensor. The colder it is the higher the target voltage. Like at 30 degrees it may be as high as 15 volts and at 100 degrees as low as 13.4. Average at normal 70 degree temps is about 14.5. The PCM also moniters the AC high side pressure through a pressure transducer that screws into the AC high side and it just works like a MAP sensor only it changed AC pressure into a voltage reading instead of vacum or boost. Course yours dont have it. The PCM will have 3 wires on the AC sensor as one is a 5 volt feed and one is a ground and the last one is the signal wire that can read from 0 to 5 volts. But when it does not have it the PCM will see 5 volts on the signal and feed wire and it will just set a default code and read a very high or low volt reading as when it see's a constant 5 volts it knows it has an open circuit and will set a voltage high code in that circuit. Ron
 
Thank you 383man. That explains where the 5v reading comes into play. It also explains why the PCM wanted 15.5 volts with the -83 degrees.
All is good now.
 
No problem. Glad you got it all fixed. Ron
 
A friend had the same issue with his 5.7 Hemi conversion, his battery would boil and and destroy itself. His guy who installed the Hemi in his truck never figured out why it would fry battery's. His best conclusion was the computer causing it, not the alternator. They switched the alternator to a GM style 1 wire to solve the problem.
 
Paul, Knowing what I know now, I would bet the PCM was seeing the same thing mine was. The battery temp being recorded in the computer as way below zero F. I don't know what the Motorola guy did to defeat that feature but it worked for my application.
 
Just a thought. Was the ambient temp sensor installed and working?
 
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