Hey guys,


I wanted some input on this issue, sense I'm about to drop a fortune on this damn thing. I don't see how this could be related but it is a pretty weird timing...


Basically I have a yellowtop optima battery up front. have had it for years and years...

In my toolbox I added 2 yellowtop batteries that are in parallel to eachother as a battery bank that I use to run an inverter for my job. The truck power system can bet switched from the front "start battery" to the rear "battery bank" using one of the battery selector switches you commonly see on boats.


If I run the back bank way down, I don't use the alternator to charge it, I wait to get home and use my plug in charger so it won't devistate my alternator..


Ok, so I put in this super helpful setup and about 1 week later the pcm died.

Coincidence?

The only thing that could be even slightly wierd is that the back battery bank is grounded to the frame near the middle of the truck. I don't see how that could be a problem... but is a consideration?


Pretty hard problem to figure out, I just don't want to fry my next 600 dollar little computer


Thanks in advance

 

What symptoms did you have to conclude a bad pcm? You already replace it?

 

Check out those grounds in a serious, obsessive manner. Is that new battery setup grounded via sufficiently sized cable directly to shiny, clean steel on the frame rails or something stout and welded directly to the frame rails? If you can get your hands on a four wire ohmmeter, measure the resistance from that new negative cable at the battery end to each of the frame rail, clean shiny metal on the bed, clean shiny metal on the cab, and the engine block. If any measure greater than 0.2 ohms, find and fix the high resistance. If you have to settle for a common two wire ohmmeter, zero the thing before each measurement and be even more diligent about reaching shiny, clean steel at each point. But if you can get your hands on a four wire ohmmeter it's the superior way to go and worth the bother even if all it tells you is that you don't have a problem at all.

If you've got a crappy ground connection it's worse than no ground at all. Say you've got a high resistance where you didn't expect it between the new battery negative terminal and the ground the rest of the vehicle sees, and hang a charger across the new battery terminals. You might have 14 volts across that battery, but because the ground connection isn't sound the voltage from the ground the rest of the truck sees to the positive terminal of the new battery could be much greater than 14V. If the new battery is isolated from the charging system at the time, no big deal. If it's switched in, though, the result can be electrical mayhem. I've seen that very thing lead to boiling primary batteries and smoked electronics.

If, on the other hand, the new battery is grounded via sufficiently fat cable to shiny, clean steel on the frame rail, and all of your factory installed ground bonding cables/straps are in place, and your external battery charger isn't failed, then it's almost certainly just a coincidence.

 

"Dash isn't cracked, steering doesn't wander, headlights are awesome, has good heat."

Haha Amen.. I cant say that^^

So, The PCM was diagnosed by a shop that I trust fairly well. It is currently being fixed/reprogramed/rebuilt. whatever that in tales..

The ground that I added is 2 Gauge welding lead, which is far larger than anything stock. same with the positive leading up front. The connection is a flapdisked shiny spot on the side of the frame that is thru bolted with a bulldog lug covered in electrolytic grease and then spray painted over. If that isn't solid I dunno what is.. the one thing I could do to insure that there is no further problem is go ahead and run my ground all the way to the original grounding location to insure that there arn't any changes to the currents in different places (I guess primarily when starting).

could you go more into depth of how the voltage can be raised by a bad ground? I don't know if I fully understand that part



Thanks for the replies