martinss

The recent thread on battery disconnects brought to light that the newer engine computers have to relearn the best settings after the battery has been disconnected, and that this can take quite a long time. As a result fuel economy is adversely affected for a period after the battery is reconnected.

So the question that occurred to me, is whether a car will also have higher emissions during this period as well? If so, then those of us whose cars have to be smog tested, might want to ensure that the cars are driven for a while before they are tested.

Since my car is currently unregistered as I restore it, and will need to be emission-tested before I can put it on the road, I would otherwise drive it directly to the test (actually I may even be required to flat-bed it according to Ontario law).

Is this a valid concern?

Mrmerlin

you do need to run the engine and it should see some full throttle applications, so to set the computer parameters

martinss

Thanks Stan. Good to know. Another thing to go on my check-list of things to do before I'm 'finished'

Mrmerlin

my 88 runs crappy after a battery reset till I give the gas a few times then all is well.

928 at last

When you actually go for the test, you're going to want the engine as hot as possible for the test itself. So, don't shut it down and sit and wait....

worf928

Actually, you want to allow the LH computer to 'see' as many part-throttle load vs. rpm conditions as practical. Mixed-driving is best.

At full-throttle the LH runs without the adaptive learning control loop and quits paying attention to the O2 sensor. So, full-throttle won't speed adaptation after a battery connection cycle.

Last, to force re-adaptation, always disconnect the battery after changing any part of the air/fuel system that can effect mixture such as injectors, MAS, O2 sensor, intake bits, etc.

A sure-fire way to drive yourself (and your wrench if thats not you) nuts is to replace a bad 02 or MAS and not cycle the battery connection.

Speedtoys

IMHO, by the time youve reached your first stop sign..youre pretty well set.

If I kill the learnt' O2 correction while running, its only a few short seconds before im back at proper AF ratios.

The "time to learn" is the statistical error over TIME to find a "best workable" long and short term O2 correction...but those are not even perfect..just "closer in general" to adjusting the WHOLE map to the condition of your car.

And..ive changed out a bad O2 sensor and not disconnected the battery, the instant correction took about 30sec, and within 5min of driving, the LT/ST corrections were pretty much reset.

If you are off 10% from bad parts, and you fix them...you have to correct from there if you do nothing, or correct from zero if you disconnect it. The LT/ST trims are going to take the same time to correct. If you are so bad that 20% correction (peak) cant get youright..might as well reset after repairing because that far out, things may not even run. :_

While sharktuning/etc when you are looking for specific differences quickly, ya...you wipe it out and run without it even.

worf928

It depends upon how close to the Factory-ideal condition the 928 is in and the distance to your first stop sign.

It can take from 0 to 30+ minutes depending upon condition, non-stock parts etc. Forced induction 928s can be recalcitrant. The Bosch Hammer can do it in 5 minutes or less.

If the 928 is all-stock and near perfect, adaptation is effectively instantaneous. Yes, I have experienced this.

Speedtoys

True, but smog run conditions..even on a boosted car, wont be messing in the fun areas of the map.

It runs to stoich pretty fast...as long as the map you have is right.which for 99.9% of us...is.

John Speake

People are mixing idle adaptation (which is usually just a few seconds at idle speed) with O2 adaptation which does need the more extended, mixed condition driving that others have recommended.

In general, if your MAF is near factory calibration then the amount of driving miles required to achieve full adaptation is going to be much less than a well aged MAF. The MAF is the dominant factor in the adaptation routine.

That's for a stock car. For modified cars, the accuracy of any fuel remapping is going to be the dominant factor in the time/miles required.

The Bosch Hammer and other testers only work on the idle adaptation part, not the O2 adaptation.