Startup high rev

[PutaLSinit]

Hi, been away from tuning for a while and was ask to remove or tone down the initial startup rev on a few trucks/SUV/all ls's. I cannot remember how to do it?
Any help would be appreciated

[johnny_boii]

Startup Idle RPM Tables

[gmtech16450yz]

RPM tables will tell it what you'd like. The airflow tables will actually give it to you. If the airflow tables aren't right, the rpm table values won't do a thing.

You posted this in the Gen 5 section, but said all LS's so I'm assuming you meant Gen 3-4? Anyway, what you want to do is lower the values in the startup air tables, specifically 12194. The first row will be key on, start of cranking. The next rows will be the amount of airflow (throttle opening) that it has after it fires up. Reducing startup flare is usually done in those rows, with a little bit of the first row reduction also. You can basically just keep lowering the values until it gets hard to fire up. Don't be afraid to make drastic changes, it's often the only way you're gonna see how the table works. You're not going blow an engine messing with this stuff.

There is also a "Startup Flare Control" table in the Spark sections, 12643. Making those values MORE NEGATIVE will drop the ignition timing immediately after the engine fires up, reducing the startup flare. Again, you can try going drastic just to get a feel for how it works. Put something crazy like -30 degrees in the whole table so you can see what it's doing. Then you'll get an idea of how much timing cut you need.

As with all idle tuning, it's a delicate balance of airflow (throttle opening) and ignition timing. (Assuming your fueling is correct obviously.) You can put 600rpm in the rpm tables, but if the airflow and ignition timing is too high, it's never going to get down to 600.

Those are the basics, there are a dozen other tables if that doesn't get your startup flare under control. (Min air, ect multiplier, throttle follower, startup time, adaptive idle, effective area, etc.) Start with those basics though. And yes, you obviously want to have the rpm values you desire in the rpm tables.

Hope that helps.

[Dano07]

Hi Gents! I know it's been a while on this post, but does anyone have experience cold start tuning on the L 86 6.2 liter? I have a 2016 Silverado with a wicked high RPM flare on cold start up. Any help on this would be welcome! Thanks.

[TriPinTaZ]

Assuming you don't have other issues, this is going to be where you address this.

idlecrank.PNG

[Dano07]

Thanks a bunch for the tip! I'm bit green tuning the gen 5 motors. No other problems at this point. I've installed stainless works long tube headers and full 3 inch dual exhaust. Also, disabled the DOD and added a intake catch can. That's about it so far. Need to get the RPMs down on startup....over 2000 when cold! Thanks again. 😀

[TriPinTaZ]

Those mods shouldn't affect the idle. Sounds more like a vacuum leak.

[lucas287]

Doesn't the high idle on cold start have to do "catalyst warmup"? ECM 2026,2027

When I set these values to 300* and -109* (respectively) I don't get the high idle, raucous cold start. I also, globally, reduced my "Base Setpoint" and "P/N" values in the ECT range that I experience here in Texas and my cold starts are very nice and predictable. (I have a Corsa Catback)

[TriPinTaZ]

Cat warmup has an effect on cold start RPM as well yes. But it isn't responsible for a startup flare as described. The Cat Warmup kicks in a few seconds after the start up.

[Dano07]

This thread is getting better. Thanks for the input gents. Keep it coming.....