bat voltage

[gto66_455]

I have a problem with bat v rising to over 20 volts, this is causing problems with ve tables. I can turn off the vehicle and restart after a couple of minutes and bat v will be back to normal and the process begins again. I have checked my voltage output from voltage reg when this is happening and it is normal. I cannot seem to figure out what is going on. I tried to post a data log but file is to big.

[rickb794]

The first thing to look at is you 5v line. If something is pulling down the Vref your bat voltage will go bonkers. The other thing to check is the voltage divider circiut that monitors the voltage.

[gto66_455]

Thanks I will check the 5v line and post results

[gto66_455]

I did check the 5v line and when the bat voltage went high I checked the 5v line and it was at 2.5 v. I checked the line and rerouted it. It seems to have fixed the problem. I will continue to monitor to insure that the problem is fixed. Thanks for your help

[gto66_455]

That was short lived. Still have problem with bat voltage. When it goes to 26v on the tuner studio the car will die. If I catch it before then I can turn off the vehicle and restart and the gauge will read 13-14v. Any ideas?

[racingmini_mtl]

As mentioned, you need to check what you have connected to Vref or internally to the 5V supply. You have something that is partially shorting the 5V to ground or drawing way more current than the supply can provide. Check everything externally connected to Vref and anything you added internally to the ECU that is connected to 5V.

Jean

[rickb794]

Remove the things that are connected to Vref one item at a time until you isolate the problem.

[gto66_455]

Solved, it was the db9 cable. I waited until the battery voltage started climbing, when it got to 16.5 afr was going real lean I than unplugged cable at ecu and everything returned to normal. I had found this in another post and thought I would try it. Thanks for the help,

[Blown88GT]

Solved, it was the db9 cable. I waited until the battery voltage started climbing, when it got to 16.5 afr was going real lean I than unplugged cable at ecu and everything returned to normal. I had found this in another post and thought I would try it. Thanks for the help,

DB-9 serial cable to laptop?
If yes, where is laptop powered from: laptop battery only, vehicle battery?
You cannot power the laptop directly from the 12V vehicle. It can cause a ground loop, which sounds like your "solved" problem. The voltage can rise far above what you would imagine. I power the laptop with an inverter which provides ground isolation.

It is not simple to explain or understand: https://en.wikipedia.org/wiki/Ground_loop_(electricity)