Can a battery maintainer ruin your battery? (Page 4/4)
theogre JUN 03, 12:40 AM

quote
Originally posted by sanderson231:
Just remember anytime the battery is disconnected the ECM goes back to default setting and the learning process for air/fuel ratio trim starts over from scratch.


quote
Originally posted by Patrick:
I've always wondered how long that actually takes. Is it a matter of minutes, hours, or days... or is it a matter of one mile, ten miles, or a hundred miles?

OBD1 ECM/PCM "learning" happens in "Close Loop" and other "Rules" met but even then only "learns" lasts few minutes at best. Most have near zero memory to save a lot of data. I suspect OBD1 "Learning" just means the computer is just using BLM and Integrator fully and while BLM often stays about same, Integrator is always moving like O2 Volts.

Main issue is can't Reset the IAC after loosing battery so Idle and Driving is "flaky" until:
Many only reset IAC after Drive > 35MPH/57KPH
Some can reset IAC when park if driver hold gas to > 2500RPM

DIS Dukes have "better" ECM and Can Reset IAC in either setup. So When I pull Battery for any reason, next run just hit the gas for ~ 20 sec. Even w/ that you often "hear" the Reset happen because engine often "stumbles" for a second or 3 depending how off the IAC is at the time.

Many IAC motors are a "servo" stepping motor w/o feedback so computer have to guess until engine has enough RPM so force close the IAC and keep running then count steps from 0 at that point.

[This message has been edited by theogre (edited 06-03-2023).]

Patrick JUN 03, 02:54 AM

quote
Originally posted by theogre:

Main issue is can't Reset the IAC after loosing battery so Idle and Driving is "flaky" until:
Many only reset IAC after Drive > 35MPH/57KPH
Some can reset IAC when park if driver hold gas to > 2500RPM



Interestingly enough, except for one Fiero (elaborated on below), I've never had a problem with my '84, '86 GT or '88 Formula's idle speed after re-connecting the battery.


quote
Originally posted by theogre:

DIS Dukes have "better" ECM and Can Reset IAC in either setup. So When I pull Battery for any reason, next run just hit the gas for ~ 20 sec. Even w/ that you often "hear" the Reset happen because engine often "stumbles" for a second or 3 depending how off the IAC is at the time.



My first Fiero was an '87 with the DIS duke, and I hated that engine. Didn't matter if the the battery was re-connected or never disconnected, it always wanted to idle at 3000 RPM for a minute or so when first started.
sanderson231 JUN 03, 12:38 PM

quote
Originally posted by Patrick:

I've always wondered how long that actually takes. Is it a matter of minutes, hours, or days... or is it a matter of one mile, ten miles, or a hundred miles?



My sense is more than 10 miles and less than 100 but really depends on how much variety there is in the driving.

There are 16 block learn cells in the ECM. Which cell you are in depends on the rpm and manifold pressure (MAP sensor) for a speed density system (i.e. no MAF sensor). The BLM values provide for feed forward control. Some call it long term fuel trim. When the rpm/MAP change you enter a new block learn cell. The value in that cell is the starting point to set the injector pulses. The default value is 128. The ECM reads the O2 sensor and when in closed loop, the ECM uses the O2 signal to bring the air fuel ratio to the desired 14.7:1. The short term fuel trim is called the integrator and the default value is also 128. The O2 sensor signal will bounce around a lot so you don't want the fuel injector pulses directly controlled by O2 signal. The integrator sort of averages (the math is more complcated) the O2 signal to provide a more stable value to control the fuel injector pulses. If the integrator is at 128 then no averaging is taking place. The learning process involves the integrator gradually readjusting the values in the block learn cells. For example if the BLM value is 128 but the integrator is 120, the ECM will gradually reduce the BLM value to 120 and that will result in the integrator getting back to 128. The desired operation is to have the integrator at 128 so there is no lag waiting for the integrator to average out the fuel injection pulses. To get the ECM to reasonablly tuned then the driving during the learning period needs to hit most of the block learn cells. When you go WOT the integrator is ignored. The ECM starts with the BLM value and then adds extra fuel to it. This is called power enrichment mode. The throttle position for PE mode varies by ECM.

When the battery is disconnected all the BLM values are reset to 128. The car is likely going to run OK but mileage and emissions will suffer until the ECM relearns the BLM values.

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formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged

[This message has been edited by sanderson231 (edited 06-03-2023).]

Dennis LaGrua JUN 05, 09:09 AM
If the power is removed with a cutoff switch my experience has shown that the ECM relearn takes about 30 minutes of all condition mainly city driving.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

Mickey_Moose JUN 06, 04:27 PM
I suspect that maybe you have a bad battery, but maybe the maintainer as an issue as well.

I use a maintainer on my car and I never have disconnected the battery while stored (heated garage for those long winters) - last battery lasted 10 years before I replaced it in 2018. Current battery still just fine.

Edit to add - really only drive the car 6-10 times a year, maybe twice during the covid years. I run the AC Delco brand with side posts.

[This message has been edited by Mickey_Moose (edited 06-06-2023).]

Patrick JUN 06, 05:10 PM

quote
Originally posted by sanderson231:

My sense is more than 10 miles and less than 100 but... <snip>



Thanks for the thorough explanation!
armos JUN 13, 06:12 PM
I've watched the datalog on my 86 V6 ECM (1227170) many times, and I'm not convinced it remembers a damn thing between restarts, at least as far as fuel trims are concerned.

Also, my fuel trims have never behaved the way everybody says they should. My INT is always high (like 170-180) and my BLMs are always at the minimum allowed values of 120, no matter what. So they're pushing in opposite directions. Supposedly the BLM should increase so the INT can come down, but that never happens, it just keeps "learning" 120s for every cell.


If battery "maintainers" can't be left plugged in, then they're not doing their job IMO. If you have to babysit them then what's the point?