Disable high Rev cold start
 

Is it possible to disable the ~1500 idle cold start. It's loud as Fuck and if you start moving a few feet right after a cold start and stop, the idle goes back down to normal 700/800 ish anyways.

Sent from my SGH-I337M using Tapatalk

With a tune it is. I believe the OFT has it reduced in their off the shelf tune and I am positive any competent tuner using Ecutek, BRZedit or any other tuning solution could do it also.

We do it in some of our Stage 2 tunes.

But that's what makes cold starts fun...

I'd leave it as it is...you risk damaging the engine without a proper warming. Just saying.

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 :)

Maybe if you peel out of your driveway... But cruising you shouldn't damage anything...

Sent from my SGH-I337M using Tapatalk

Can the Unichip / Flux2 do anything about changing the cold idle level?

Maybe @Unichip Jack could chime in here?

Because Race Car

I don't think so, the Unichip doesn't get input from the ECU. Without talking to the ECU it has no way of knowing why it is at that RPM, for all it knows, you're coasting. The only things it can detect are throttle position, timing/cam position, and air flow.

It's there to get the liquids up to operating temperature and warm the cat up before taking off. I always sit for the full time when its cold outside. It's an extra 30 seconds. I also put a quieter exhaust on with my catless header so I'm not a jerk in my apartment complex. Even then, my car is still fairly loud cold start.

There's two levels of the cold start program.

1) Higher revs, and tons of valve overlap. This is WAY louder. After a few seconds the revs stay up but it's much quieter when the ECU scales back the overlap. This is 100% to get heat into the cats faster. I would have zero issue disabling the overlap part (or minimizing it), it's bordering on obnoxiously loud for no good (to me) reason.

2) Normal higher revs, normal valve overlap. This is the part meant to get heat into the fluids. I wouldn't want to get rid of this.

^^ This guy gets it! :D

I think the best way to look at this is simple. Drive the car easy until fluids are warm. Most people don't wait once they start their car and take off before the cats have a chance to warm up.

Even with the loudness on the cold start, I kept it with my 3" exhaust. Sure, it was brutal, but I didn't care, lol. No complaints from the apartment complex!

I will look at my logs in a bit for overlap and throttle angle but, a big component is the afterstart timing. The default after start timing is -15, when the high cold start idle drops the timing does back to the normal +13 - +15 degrees... this is easy enough to edit and does change the noise level but it also creates stability issues for the idle system and can throw numerous codes.

I'l still messing with it. at one time i had set the after start timing to 0 and it would throw an ignition timing out of range code or somethings like that but it was a lot quieter.. The idle rpm also went up. at the time i was not messing with the idle speed tables.

my neighbors might be happier about me getting OFT more than me, lol.

I found these for the STI's, just a word of warning from one of the experienced techies:

High RPM & retarded spark provide heat to warm up the cat. -15 degrees (BTDC firing, so 15 ATDC firing) is about average spark retard on a modern direct injected engine during cold start. I'd have to take a look at the injection timing. If it's running just DI, you'll usually have two injection events, roughly 50/50 or 60/40 split between the first and second event. The first is in the intake stroke, around 240-260 BTDC firing. The second is on the compression stroke, roughly 40-70 BTDC firing. This stabilizes the combustion enough to allow retarded spark. If the engine is cold enough you'll just see a high rpm idle, single injection event, and maybe less retarded spark. It's focused more on warm up and less on emissions, because there are no emissions tests taking place colder than 20F/-7C ambient.

I haven't seen charts on the cam grind vs crank angle, but the valve overlap burns up the HC emissions if intake valve ends up opening BTDC intake. It's commonly used on Japanese cars.

What happens is, the HC emissions are ejected mostly when the exhaust valve opens and when it closes. If the intake valve is open at the end of the exhaust event with piston still ascending, that HC goes back into the intake port where it can be burned up on the next cycle.

http://www.ft86club.com/forums/attac...1&d=1389711457

One last thing to keep in mind. The stock tune was designed to start and idle ok on really crappy fuel (does not vaporize well) in very cold climates. That's one of the reasons why it behaves the way it does. There are special lab-grade "heavy startability fuels" that's used to test this. So there is a certain safety margin you are seeing in the stock tune. One of the side effects to that can be NVH concerns.

unless you take prestine care of your car (high grade fuel, warm~steady climate, frequent oil changes and meticulous observation of the various readouts... i wouldn't fuck with the car's warmup algorithem.

OK, looked at some logs. Cam timing does not change after it kicks down from high retarded timing idle. Direct injection timing does though. During the retarded timing high idle, the DI fire angle is 45* as soon as it bumps down to regular ignition timing fast idle the injection timing goes to 320*.

So, during the high retarded idle the injection is also retarded to help put more energy into heating the cats. So far i have not seen a table that has an injection timing adjustment for this phase of the cold start.

Some of the posts in this thread seem to be talking about the valve overlap changing for cold startup idle. I was under the impression that the FA20 doesn't have the ability to to change valve timing... Am I missing something?

its dual VVT so you can change inlet and exhaust timing and overlap between

whether you can access the cold start functionality to cure this high startup revs is another matter

Yes.

It has AVCS on intake and exhaust cams. Basically, a hydraulic cam phaser moves the cam centerlines. Intake cam can be advanced from the most retarded position, and exhaust cam can be retarded from the most advanced position. This allows overlap if the cams are phased far enough.

Now, it depends on the grind of the cam. If the intake valve opens at 20 degrees ATDC intake, and exhaust closes at 10 degrees BTDC intake, you need over 30 degrees of intake cam advance to create overlap and backflow into the port.

Is PFI running in your log?

So is the valve overlap messed with for higher RPMs? Because that would means these engines have variable valve timing and I would be surprised that it isn't making more power in the top end. Granted it wouldn't change profiles as vtec engines do.

Valve timing it can do, valve lift it can't.

Makes sense, thanks!

Interestingly, there was a generation of Subaru engines that did have both AVLS and AVCS (i.e. timing and lift) - the older H6's.

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.

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):

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.

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..

http://www.ft86club.com/forums/attac...1&d=1389742684

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.


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.

http://www.ft86club.com/forums/attac...1&d=1389742684


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.

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.

http://www.ft86club.com/forums/attac...1&d=1389750626

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.

http://www.ft86club.com/forums/attac...1&d=1389750626

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.

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.

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

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.

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?

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?