dsrour

anyone have ideas on keeping power to pcm when disconnecting battery?
Does it make sense to do this so the learned parameters arent lost or is it no big deal for pcm to relearn. thanks

G-Body

iTrader: (4)

I have not found it to be a big deal for the PCM to re-learn. In fact the only time that I have noticed it is when the PCM was disconnected for over a week, then when I would start the car I would have to hold the throttle open for the PCM to re-learn the idle control.

Anyway you can buy a product to do just that. It has a connector to plug into the lighter plug and on the other end you connect a 9v battery. It is intended to keep power to the radio and that so that you don`t lose your presets, but it should also keep power to the PCM.

thunderstruck507

iTrader: (18)

yup they have 2 versions, 1 for old cars and 1 for computer cars, just for that reason

Stu Cool

iTrader: (13)

You can run your 12v unswitched PCM power to the battery side of your cut off switch and put a 3 amp fuse in it. That way the PCM will be powered even when the switch and everything else is off. Car won't start or run and the fuse will blow if any load beyond the PCM is encountered. PCM will have power to retain its settings

Pat

dsrour

Thanks very much for the suggestions. Pat I like your idea since it is automatic.
Dave

Oscar Will

I did as Pat suggested long ago........never had a problem, the car can sit for a month and still start just fine.

Carshopinc.com

iTrader: (5)

I have had ls1 cars really act up upon start up after being disconnected and some that start and run perfect.... I would suggest running the 12 constant to the battery side of the switch...

Stu Cool

iTrader: (13)

I gotta give credit where credit is due. Thanks John at Speartech! He is the one who made the suggestion to me.

Pat

Old Geezer

iTrader: (3)

AAW has a neat little jumper that does this. As I understand, if it goes open, once the load is reduced to it's limit, it resets. No fuse to change.

NoahSuthy99

Any idea which pin on the pcm is 12V unswitched power?

LSswap

If you're worried about the fuse blowing, then maybe try this. The fuse will never blow no matter what kind of loads you leave on.





Personally I don't think you can backfeed power from the 12V unswitched pin. I would try this instead.




Note: My ECM does not lose settings on power down, so I have not tested this.

1964SS

iTrader: (1)

It all depends on which pcm you are using. check lt1swap for specific harness and pinouts.

https://lt1swap.com/wiringharness.htm

NoahSuthy99

Just to update everyone, I found the solution. My PCM is a PO1. Pins 20 and 57 on the blue connector both run to the (pcm batt) fuse on the stock fuse block, so I ran constant hot from the always live side of the disconnect up to those two wires and disconnected the wires going to the fuse block. VERY important you cut off those wires going to the factory fuse block and remove the fuse or else you will basically be powering the entire car. I ran a 12 ga wire back through the car with a 10 amp fuse in line and it seems to work perfect.