Start procedure after using cutoff.

You should also wait 30 seconds after key-on before spinning the engine over.
This lets the various computers find their operating points.

 

If i’m not mistaken, the 10 min idle after battery re-connect is only applicable to M2.7 cars (not 5.2).
As mentioned in a cold start thread, doing the 10 min idle after batt connect did fix the “stall on cold start” problem, but the car seems to relearn old habits rather quickly and ends up stalling on cold start (again M2.7 specific). All that to say yes, letting it idle after batt reconnect does have a noticeable difference on the behavior.
Just out of habit I leave it in the key-on position until the buzzer stops (10 sec-ish), before cranking over, but have never heard of a requirement to do so for computer module calibration. Is this documented somewhere?

 

Andrew - I don't recall if it's documented for 355's but I know it is for other models such as the 599.

 

I just scanned the owners manuals for both and sure enough - the re-learn is in the 95 manual but not in the 98 manual. Good to know as I thought this applied to all.

 

If the re-learning is not in the 98 manual (so the 5.2), it could mean that there is no re-learning ability. It might also mean that a reset cannot be performed by switching off the power to the ECU.
Or is that conclusion too simple?

 

The 5.2 may not be subject to the same 10min learning procedure, but it certainly does learn and will run different after being reset.

 

Any ideas on why the cars seem to relearn the bad habits? Old sensors, intermittent bad connections, changing operating conditions (temp, barometric pressures, fuel, etc.), slow ECU chips, or just one of those quirks/character? I need to reset the ECU and do the warmup procedure every so often as well. I was thinking maybe it was a sensor issue or user error. It is really interesting this seems to be somewhat commonplace.

 

348-2.7 needs every sensor to be below 64-65 degrees (cant remember off my head) for a full complete reset.
Turn key on, wait 20-30 seconds for battery voltage to stabilize then start. Do not turn lights on, ac, hit brake or windows.
Let idle until engine comes to temp and cooling fan kicks on. Once the fan shuts off all perimeters should be set. A little longer is better then less time. I let mine cycle twice on the cooling fans.

 

User error then. I normally just idle until the first fan kicks on. I also don't think it's been cool enough this year to start with the sensors below 65*.

 

5.2 has obd2 readiness monitors

 

Idle speed (at least) requires the 5.2 ECU to relearn for 10 minutes. It's mentioned in the 5.2 section in the WSM on page C23

 

Yes and it does make a differance. I always let it idle anyway.

 

It should not matter if the air temp is different. The MAF senses the mass of air entering the engine, not volume. Air density varies with temp. Thus the MAF automatically compensates for temp. For the same volume flow it sees more mass at lower temp the ECU will increase fuel delivery to give the correct A/F ratio. A/F is mass of air divided by mass of fuel. Some cars have air flow meters, AFM, which measure volume flow. They usually also have an inlet air temp sensor as well. With the temp and flow known the ECU can figure the aid mass flow.

 

Dont worry see below

With the sensor temps, water air engine etc are below X the ecu will set a cold start best case scenero. If it's all sensors calibrated @ 80 degrees then cold start values are optimized for 80 degree cold starts.It just sets the "choke"
These old ECUs have no real bells whistles or magic sauce.They are as simple as can be and have no modern features as we know today.

So what John says is 100% correct, you get what you need. If your average cold day is 80 then the car figures it out

 

I return back to the magical red (expensive to repair) car, turn on the master switch, turn the key part right after and drive out of the parkade. Emediatly after this procedure, I find out what kind of sounds it makes. This all makes my time away from her worthwhile. Oh, it's a 5.2

 

If the ecu "learns" the choke value at 80, and the next start is at 50, would it essentially need to relearn the process for the lower temperature and warrant another long warm up?

Growing up around diesels and muscle cars, letting any car warmup is ingrained into my brain, for better or for worse. I definitely don't do the 10 min every time but enough to make me feel like the thermal expansion of everything has started and the oil has a bit of heat. I'm wondering if the ecu is still calibrating on a cold day when I depart. This might explain why the car seems to "forget" how to warm up. I'm probably over thinking it. It's not rocket surgery after all.

I'm just happy I don't have to set points or tune a carb

 

Tim was using a figure of speech. There are basically two options. Cold start and hot start. Which is determined by the coolant temp sensor. Cold start puts the ECU in "enrichment mode", if you will. That is, from the MAF the ECU the air mass flow and adds fuel above the normal value, like a choke. So at cold start, instead of an A/F ration near 14 it might be around 12 due to extra fuel (values are for example only). With a hot start it would remain around 14. But this has nothing to do with resetting the ECU. The idea of letting the engine run for 10 minutes is precisely to get it up to operating temperature and setting the ECU parameters in closed loop mode, idle conditions.

 

Yes but not just 2 options of cold/hot start. Even the oldest EFI systems would vary commanded equivalence ratio (percentage difference to stoich) vs coolant temp and manifold pressure.

For example, it would command more fuel at 40deg than 45 and even less at 50, not just a single temp break point between cold/hot.