Disable high Rev cold start

[arghx7]

Originally Posted by Raven604

IF its so important to keep the idle to high on a cold start why can you start the car cold, immediately drive the car a foot or two and have it drop down to normal idle. Why wouldnt it continue to have a high idle until its "warm"

Maybe @mad_sb can post his logs and I can make some charts to explain a little further. You can go second-by-second and divide a cold start into different sections with different priorities for tuning: Cranking, run-up, idle speed flare, settling down, cat lightoff, gear shift, drive away.

That first few seconds of high idle is the most important for a stable start and idle. It's also the most important for cold start emissions. A lot of that exact behavior was put in there to meet a very specific emissions & fuel economy test cycle. For example, in the US Federal Test procedure, the driver begins in neutral and has to put the car in gear 15 seconds after cranking and then begin driving after 20 seconds.

[mad_sb]

Originally Posted by arghx7

Is PFI running in your log?

Yes, cold cranking is 100% port, once it catches and fires up into high idle mode it is dual fuel (port and direct). Once it idles down and the load drops but before it is fully warmed up (switched to direct only idle once fully up to temp) it is port only at idle.

That logic follows the normal injection ratio tables, once you are out of retarded timing idle mode the DI firing angle follows the GDI tables (all 3 look like the attached):

[mad_sb]

Originally Posted by Raven604

IF its so important to keep the idle to high on a cold start why can you start the car cold, immediately drive the car a foot or two and have it drop down to normal idle. Why wouldnt it continue to have a high idle until its "warm"

Have you tried to drive the car with the timing locked at -15 degrees? Runs like pewp Seriosly though, they probably just have an exit routine in the code that says if the car is moving, cancel the cat warm up sequence.

[mad_sb]

Originally Posted by arghx7

Maybe @mad_sb can post his logs and I can make some charts to explain a little further. You can go second-by-second and divide a cold start into different sections with different priorities for tuning: Cranking, run-up, idle speed flare, settling down, cat lightoff, gear shift, drive away.

That first few seconds of high idle is the most important for a stable start and idle. It's also the most important for cold start emissions. A lot of that exact behavior was put in there to meet a very specific emissions & fuel economy test cycle. For example, in the US Federal Test procedure, the driver begins in neutral and has to put the car in gear 15 seconds after cranking and then begin driving after 20 seconds.

Sure, here is a log from this AM. Note that I am on high Ethanol content E85 (my test-tube style test kit shows E95) so my cranking pulse widths are way up there.

Also, see the attached pic of how my idle tables are set for this log and notice that the target idle rpm does not seem to pay attention to the target idle tables shown here during the retarded idle phase.. maybee it does try to adjust to hit the target.. hard to tell. Could be to do with the initial load and or airflow reference tables.. also shown..

[arghx7]

Here's how you can divide the cold start up. You have cranking, run up, flare, then a transition to catalyst heating mode. There are different priorities and goals in each portion of the start event. These are related to starting time, quality of initial combustion, engine out emissions, and catalyst heating energy.

Originally Posted by mad_sb

notice that the target idle rpm does not seem to pay attention to the target idle tables shown here during the retarded idle phase..

There's probably a different set of controls that hasn't been reverse engineered at this point. That's Injection Mode 3, which must be the mode for stratified combustion/catalyst heating.




Look at the middle plot. Black line is injection mode--you can see it changing during the different phases of the start. Notice how that corresponds to changes in start of direct Injection (purple) and spark timing (top line).

So during injection mode 3, you have retarded spark, late injection timing in the compression stroke for stratified combustion, and a high idle. In injection mode 1 you can see that we are back to intake stroke injection with the early start of injection.

[arghx7]

A couple more... based on what I am seeing so far in this log, the AVCS isn't really doing anything in the starting process. Keep in mind that coolant temperature is about 23C. It might behave differently at other temperatures.



So intake cam is gray line, blue line is exhaust cam. Intake cam barely moved, exhaust is at 0. 1 or 2 degrees movement isn't going to create meaningful overlap. Maybe under other conditions the cams move. Usually, with a regular oil pressure hydraulic phaser you'll see the phaser move after the engine starts if it was tuned for cold start cam phasing. It takes some time for oil pressure to build up, and the cam phaser is difficult to control when cold.

If the engine has an electric cam phaser it can move immediately. Some engines have a regular oil pressure operated phaser but they can park the cam into an overlap position for cold start. This is to get immediate reburn of HC emissions during cranking--saves money on an expensive and restrictive cat. Other times you'll see the cams move on cold start, but it doesn't actually dial in overlap. It depends on how far the cam moves and what the grind of the cam is. The overlap can cause unstable combustion...it often needs certain tricks to stay stable, like late intake valve opening, tumble or swirl control valve, or restrictive intake port.



This graph shows a high pressure start, where the fuel pump ramps up pressure as fast as possible. 12-13 MPa seen here is typical on direct injection. It's needed for proper atomization of the fuel during stratified combustion. It's also possible for the whole engine to run at low fuel pressure (PFI pressures) as a failsafe. Think about all those BMW N54 engines that were driving around with jacked up fuel pumps back in the day.

[Deep Six]

Wow, talk about information overload! Honestly I wish I understood half of what was just discussed but what I do know is that the 1 or 2 minutes of 1500 rpm idle at startup has no appreciable affect on coolant or oil temps as neither move much more than 10 degrees in that short span.

[Raven604]

Yes so much more information than what I needed but good to post it up anyway. Thanks guys.

Sent from my SGH-I337M using Tapatalk

[wparsons]

Originally Posted by Raven604

IF its so important to keep the idle to high on a cold start why can you start the car cold, immediately drive the car a foot or two and have it drop down to normal idle. Why wouldnt it continue to have a high idle until its "warm"

Not sure about your car, but I start mine in the garage and then almost immediately back out into the driveway (so backing up about 15 feet) and it's still at the stupid loud high idle after backing up.

[Andrew025]

Originally Posted by wparsons

Not sure about your car, but I start mine in the garage and then almost immediately back out into the driveway (so backing up about 15 feet) and it's still at the stupid loud high idle after backing up.

I do the same thing as you. As soon as I touch the gas RPMs jump up a bit but settle down to normal idle immediately though.

[wparsons]

Originally Posted by Andrew025

I do the same thing as you. As soon as I touch the gas RPMs jump up a bit but settle down to normal idle immediately though.

I'm going to bet it's temperature related... winter temperatures here are averaging below zero C, what's the average morning like in Portland?

[Wepeel]

Great info. So how does this relate to the occasional loud "pops" I hear on certain startups? I've heard it has to do with catalyst warming but is there funky stuff happening with the AFR that is causing odd combustion events?

[Raven604]

Originally Posted by Wepeel

Great info. So how does this relate to the occasional loud "pops" I hear on certain startups? I've heard it has to do with catalyst warming but is there funky stuff happening with the AFR that is causing odd combustion events?

rut ro. i never hear loud pops. maybe your DI seals are gonzo?

[shaunsweeney]

Originally Posted by Clipdat

I'm not so sure about this statement. I believe I have read elsewhere on the forums that the only point of the overlap/high idle upon cold start is to kick start the CATs to reduce pollution and meet emissions requirements.

Without this behavior hard coded into the stock ECU flash, the car would start up and have a natural high idle for a period of time, and then slowly drop - much like almost every other car on the road.

I've personally noticed that on super cold starts (around 30 degrees F), the high/overlap idle will do it's thing and then stop, but the idle will still stay high for another minute or two before finally dropping down.

I'm torn on it though myself. Part of me would want to turn it off so my early morning weekday starts aren't so obnoxious and neighbor-waking, but part of me likes how loud and crazy it sounds... because racecar

Hahahahaha you mean in mild temps?!