4 times this year, I've had to jumpstart my car, mostly after it had sat for a week or more, but this week... no crank after sitting 10 days, charged battery fired right up. Still fired right up 3 days later (last night) and this morning.

When I went to start it at lunchtime, no crank. I had left my laptop plugged into it for those 4 hours.

The battery is very old, and I'm gonna replace it, but...

I did the current drain test, and something is pulling 18 milliamps.
Unplug main fuse for the Holley c950 EFI the drain goes away.

Anyone know how close to normal this is?
With Yellowstone coming up, I really need to be able to rely on her to start.

why not use one of those negative battery cable disconnects Jim? I do and never worry about the drain then. :D

That's not too much of a drain, but why does the ecu need that when the car is shut off? Is it supposed to be connected to an always hot lead? What would happen if you routed it to an ignition hot wire?

alan

It has 2 power leads, like a modern stereo, 1 to IGN, 1 to BAT.
It's not much of a drain, less than .02 amps, but it still seems like more than it should be.

Connect a 12v test light between the neg cable and the batt post. If the light glows (even if very dim) then you have enough draw to suck down a batt.

Start disconnecting fuses untill you find the circuit that is causing the issues. This is the best/fastest/easiest way I know of to find/isolate a drain.

Having a clock, ecu, stereo, etc will not be enough draw to make the light glow. Ive done this my entire automotive career and its never failed me. (Ive done ALOT of electrical gremlin diagnosis on modern cars over the years)

Good luck and report back what you find. :thumbsup:


Chris:cool:

ahhh, thanks chris, but I've all ready done that, with an ammeter. Drawing .017 amps, isolated to the Holley Commander 950 ECU.

If a switch is put into place on the power cable and activated, would not this action lose the memory already gained by self learning of the ECU?

Most modern cars typically 'go to sleep' if current requirements are less then 45 ma, down to 15 ma.

I calculated for 10 days the power used is equivalent to 173 amps total.

Well Jim, like Evertt said, it adds up. Mine does the same thing. A suggestion. Don't rely on one battery for those special trips and cruise nights. Get a two-battery trunk kit. Leave one disconnected for emergencies. I'm not going to be so pompous as to tell YOU how to wire it.
http://epitomesrebuild.com/images/268.JPG

If a switch is put into place on the power cable and activated, would not this action lose the memory already gained by self learning of the ECU?

Most modern cars typically 'go to sleep' if current requirements are less then 45 ma, down to 15 ma.

I calculated for 10 days the power used is equivalent to 173 amps total.

Is that figure for most cars? Wouldn't that imply that all car batteries in modern cars would be dead if we go on vacation for 2 weeks? Wonder how other ECU's handle this issue? Never had that issue with any of my cars which all have ECU's.


alan

I worked at Lexus and we had a few problems with cars draining the batteries.
We found that if the car had more than a 50 milliamps (from the factory they had about 20-30 milliamps of draw) it would start cause problems with dead batteries.
We had a customer with a 70 milli amp draw and a brand new battery, it took him about 3 weeks to go dead. (and he said it almost started)

So with a 17 or 18 milli amp draw I would say the problem lies in the battery, get a yellow top optima or some other good battery and I will bet that it takes care of the problem.

Oh, and how many amps do you think the laptop was drawing to charge the battery? I don't know if the cig lighter had power with the key off, but if it does that probably caused the dead battery.
My laptop has a 100 watt power supply that would be 8 amps, that would kill the battery for sure.

Iget a yellow top optima or some other good battery and I will bet that it takes care of the problem.
On my way to do just that very shortly. Think I'll drive it and change the battery in the parking lot!
Love to hear those new pipes sing!

ok, one nice new battery from autozone, installed in thier parking lot.
Time will tell now, but I expect all will be back to normal.

Jim 18 mA is less than a simple LED and I can assure you that won't phase a healthy battery for weeks on end.

Your old battery just couldn't hold a charge very long.

I can leave my Harley alarmed for 2-3 weeks and she fires right up.

Four years is about tip tops for a modern battery, anything more and it's borrowed time.