Testing Battery Drain 3

Hmm. It looks like battery drain is going to be a common subject on this blog. The most recent was an '03 Dodge Ram 1500 with a complaint of battery going dead after sitting. The customer had spent several dollars trying to get a fix at other shops but still had the problem. Now the truck came in on a tow because the battery was dead and wouldn't start with a jump. I used the jump box and got the engine cranked to get the truck into a work bay. I didn't need to use the memory saver because the battery was already dead. I just disconnected the battery cables for a quick battery test. The battery tested bad so I installed a known good battery to use while checking the electrical system. I put the original battery on a slow charge. I would re-test it after it was fully charged.

With the good battery on the truck and after giving it time to "timeout" the modules, I checked the actual battery draw which was well within specs. So there was no excessive drain on the battery at this time. 

I had to halt testing at this point after I was rudely interrupted by quitting time and my stomach growling...

After an overnight on the charger, the battery was 100% charged and I installed it on the truck after removing my known good test battery. I gave the truck several starts while running accessories to get rid of surface charge. This battery still tested bad. I removed the bad battery and re-installed my known good battery because before I called the customer with a report I still needed to test the charging system. The idle rpms were very erratic on the truck so my voltmeter was dancing quite a bit. I could see I had alternator output but I needed to fix the idle problem. 

I should explain something. The engine computer has a learned memory that can be cleared with a loss of battery power. One of the typical things the computer has adapted to is throttle plate coking or buildup of carbon at the throttle. As the dirt/carbon/crud built up at the throttle the engine computer made changes to its idle strategy and those changes became learned programming. Loss of the battery power here cleared the learned memory so that when I started the truck it fell back to the original idle strategy and not an adapted one. In other words, it idled poorly now because it wasn't compensating for the dirty throttle bore. I could either let the truck run and operate long enough to relearn idle or, since the problem was a dirty throttle, clean the throttle. I usually choose to clean the throttle. I was right about the throttle I see. 

After cleaning the bore and plate the idle was steady and the voltmeter showed a good alternator output. 

In the meantime the customer had picked up his original (bad) battery and taken it to the store he purchased it from a year ago for an exchange. After doing the cleaning and idle repair with my battery installed I didn't want to chance losing what I had gained with another memory dump so I connected a memory saver while making the swap back to his new battery. 

I think I've covered it all. Good fix!

That's the magic. 

Kenneth Hayes

G&G Auto Repair