insights on a strange DC electric phenomenon?

bulmart wrote: "What could be going on?"

To answer your question the best I can. Every lead/acid battery I've ever seen/tested, even if sitting on a shelf connected to nothing, WILL slowly discharge over time. (that's why battery minders for rarely used batteries are a good idea) It's just the nature of the beast. As previously mentioned, you can assure yourself that if your house/chassis batteries are in the system in any way, there are some parasitic loads on them and they will slowly discharge over time. Age is another factor. Older batteries generally lose their charge faster that newer ones. When a lead/acid battery works, small lead particles of the plates slowly slough off and drop to the bottom of the battery case. Eventually the debris piles up high enough to touch the bottom of what's left of the plates and one or more of the battery cells shorts out internally. You can't see that looking at the outside of the battery. Usually, but not always, when that happens, the battery is done.

Chum lee

gatorcq wrote: "ECM do have RAM, but all the memory is Non-volatile. Meaning it retains it's info without power. On all coaches after 1996, the ECU is powered down. Meaning power is removed from it. So look elsewhere."


Hummmmmmm. I'm not so sure about that. Please explain to me why on my 1999 Southwind Storm Ford F53 chassis 6.8 liter gas V10 @ 62,000 miles, if the check engine light comes on and stays on for say . . . . 500 miles with multiple cold restarts, if I disconnect the negative chassis battery lead for several minutes, the fault code(s) clear and the SES (Service Engine Soon) light goes out and stays out until I hit some hilly terrain. This works 100% of the time. The fault code set is for too low octane gasoline. (it's kind of picky about low octane fuels) I buy the recommended 87 octane (or higher) fuel but I'm not sure I always get it.

Are you saying that the fault codes are not stored in the ECM?

Chum lee

And they are tricky. The draw may be 100 mA for several minutes after key off, then suddenly drop to less than half of that. Other parasytic draws include the radio ( some part of it is drawing power all the time, perhaps the clock), the radio waiting for the remote to call, alarm system, etc.

As for non-legitimate loads, I had a 4 inductor trailer type Jack connected to the battery with nothing plugged into it, and it drew 75 mA for no reason at all.

Measure, measure, measure, indeed. Careful with the low current ranges on a multimeter - if somebody opens a door, turning on ceiling lights, the current can jump by a factor of ten to burn out the range on the meter.

Got GNUS for you. Measure ma into ANY ECU and weep. Theory versus reality.

if i disconnect engine batt, upon reconnect and start engine, it sputters, might stall, and runs rough for a couple minutes

ECM do have RAM, but all the memory is Non-volatile. Meaning it retains it's info without power. On all coaches after 1996, the ECU is powered down. Meaning power is removed from it. So look elsewhere. By the way, it does not relearn how you drive. On newer autos, it is always learning how you drive and changing.

?

MEASURE

MEASURE

MEASURE

ECU's are not autonomous. They have ROM, RAM and DRAM, EPROM, and they consume power to some degree.

Make your own cigarette lighter feeding power supply. All's it takes is 12 volts worth of any battery, and a wire and plug.

Connect the alternate power supply to the cigarette lighter plug.

Disconnect the battery negative cable.

Connect your digital multi-meter across the disconnected negative battery cable. Be sure the meter leads are plugged into AMPS and not MILLI-AMPS. Set the dial for AMPS

Yank the plug on the cigarette lighter 12 volts.

Go read the amperage on your multi-meter.

Be sure the car interior light, glove box light and any other lights are not burning, when you do this.

If under 1-amp, reconnect the cigarette lighter power supply then switch the leads to MILLI-AMPS and turn the dial to MILLI-AMPS

Disconnect the lighter plug power supply once again, then go read the milliamp draw on the meter.

I intensely dislike quiescent draws of 50 ma or more.

But when you reconnect, the non-loss of power to the engine ECU will have retained ECU calibration. No rough starts or stalling.