Making an offboard for tuning
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Location: Cleveland, OH
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I have heard of people with bonnies having problems writing PCMs with tuners while the PCM was in the car, with some DIY directions and a trip to Morad, one of the benefits of living in cleveland
, i got it all fabbed up and am proud to say i have had a 100% success rate of writing PCMs
unfortunately i didn't think to take any pictures while making it but heres the end result
![](https://www.gmforum.com/howto/tech/post-131-1137717409.jpg)
here are the connections that need to be made
![](https://www.gmforum.com/howto/tech/100_1198.jpg)
here is the connector, it is the blue harness from the pcm and the OBDII connector, the 2 wire hanging out are for power
![](https://www.gmforum.com/howto/tech/100_1199.jpg)
the battery charger i use to power everything, this way no losing the pcm mid-write due to low battery voltage
![](https://www.gmforum.com/howto/tech/100_1200.jpg)
offboard and power
![](https://www.gmforum.com/howto/tech/100_1201.jpg)
simply connect your pcm, don't forget to tighen the screw![Wink](https://www.gmforum.com/gm/images/smilies/wink.gif)
![](https://www.gmforum.com/howto/tech/100_1202.jpg)
then all i have to do is connect my dhp interface
![](https://www.gmforum.com/howto/tech/100_1203.jpg)
turn on power, i used 12 low at first b/c i didnt wanna fry the pcm, but couldnt connect so i tried 12 high and no more problems, not in the pic but there is a switch for ignition power built into the harness
![](https://www.gmforum.com/howto/tech/dhpwrite.jpg)
mid-write, battery voltage is showing ~14v
![](https://www.gmforum.com/howto/tech/dhpwritedone.jpg)
and success! all done in about a minute
BillBoost recommends using an old computer power supply or 12V power supply from Radio Shack for overamperage protection.
if anyone is interested in parts for making one i can get them pretty cheap, or i could get the parts, fab it up, test, and ship it to you
![Very Happy](https://www.gmforum.com/gm/images/smilies/biggrin.gif)
unfortunately i didn't think to take any pictures while making it but heres the end result
![](https://www.gmforum.com/howto/tech/post-131-1137717409.jpg)
here are the connections that need to be made
![](https://www.gmforum.com/howto/tech/100_1198.jpg)
here is the connector, it is the blue harness from the pcm and the OBDII connector, the 2 wire hanging out are for power
![](https://www.gmforum.com/howto/tech/100_1199.jpg)
the battery charger i use to power everything, this way no losing the pcm mid-write due to low battery voltage
![](https://www.gmforum.com/howto/tech/100_1200.jpg)
offboard and power
![](https://www.gmforum.com/howto/tech/100_1201.jpg)
simply connect your pcm, don't forget to tighen the screw
![Wink](https://www.gmforum.com/gm/images/smilies/wink.gif)
![](https://www.gmforum.com/howto/tech/100_1202.jpg)
then all i have to do is connect my dhp interface
![](https://www.gmforum.com/howto/tech/100_1203.jpg)
turn on power, i used 12 low at first b/c i didnt wanna fry the pcm, but couldnt connect so i tried 12 high and no more problems, not in the pic but there is a switch for ignition power built into the harness
![](https://www.gmforum.com/howto/tech/dhpwrite.jpg)
mid-write, battery voltage is showing ~14v
![](https://www.gmforum.com/howto/tech/dhpwritedone.jpg)
and success! all done in about a minute
BillBoost recommends using an old computer power supply or 12V power supply from Radio Shack for overamperage protection.
if anyone is interested in parts for making one i can get them pretty cheap, or i could get the parts, fab it up, test, and ship it to you
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