Hard starts when warm? I may have a fix, come on in!!

[xc_SS/RS]

I was checking out my tune and noticed there is a table which has values for cranking spark advance and I found something fairly interesting. It may also be the cause of our bad starts when warm. I think this is the main cause of our problems. Not that the other solutions are wrong or bad, but this will make the largest change.

Basically, when the car goes to start the ECU looks to this table for spark advance values to use to fire the motor. It's values are based on coolant temp and engine speed (RPM).

So, you want to start the engine after moving it in the driveway and the coolant temp is 110 degrees. Spark advance? 12 degrees. It's gonna start up great.

You want to start it right after getting gas and the coolant temp is 212 degrees. Start up advance? 3 degrees that will switch to - 10 degrees at 100-200 RPM. Wtf??

Your engine isn't gonna want to start well at all in the 2nd scenario. So I made a slight change to this table and I have definitely made an improvement to hot starting issues. Here are the stock values, what I'm using to compare with, and my values:

stock cranking advance values:



as you can see for ECTs up to 175 you will get good start up timing and for 176+ it will slowly reduce itself to equal -10 degrees at 100-200 and 250-500 rpms. this is why, when the engine is hot, it will start, stumble, and then catch itself to slowly get into its idle speed/spark settings.

the example i am using is from an E67 ECM/PCM/ECU that you'll find on a 2009 CTS-V (LSA V8):



You can see that at 176 degree ECT the CTS-V has 2 more degrees of timing advance during cranking, and the big one is it goes up to 10 degrees (thats a 20 degree swing in some cells!) for 212-284 degree ECT! huge difference when you compare it to an LS3 tune (camaro, corvette, or even a crate motor tune) and it explains why they start up so well.

onto my adjusted cranking values:



all i did was change the -10 degree values to equal the positive values in their row. starts up great as it is but i think i will add another degree for 176+ cells just to help it a bit more.

here are the graphs:

stock:



cts-v:



mine:



i think it helps, and once i saw the cts-v table i felt pretty confident this is alright to do. keep in mind you will need to adjust the start-up flare table to make sure the engine doesn't rev up like crazy.

christian: i'm sorry but screw your starter. i've got a stock starter powered by a smaller battery than stock and mine cranks like magic.


BUT WAIT, THERE'S MORE! So because this is a Camaro forum dedicated to the 5th generation model, i present to you: the stock cranking spark values and graph from a 2013 Camaro ZL1 with an A6 trans:

values:


graph:


A Camaro ZL1 and CTS-V CAN experience heat soak because of their supercharger. An LS3 (well most of em at least) don't have a supercharger adding excessive heat to the motor. So they gave us less spark advance, but it's barely enough to get the motor going when hot. Changing the values to the positive 3 degrees or 2 degrees made a huge difference to hot starts.

I have also done other things that have helped make my hot starts better (thermostat is #1 given it keeps coolant temps lower) but this is easily the top change now.

I hope this helps someone!

[Roader]

Good writeup. We tried something similar to this before on my car and helped somewhat but always has a slow startup

[PepeLePew]

Wow very thorough. Nice research and explanation! I love the seeing the data like this. If I am ever plagued by the non-starting issue when hot, I'll remember this.

[eLeSthree]

Cranking spark is something any decent tuner will change right off the bat even on just a cam tune.

Also, if you're running large injectors and you have doubled stoich and cut IFR in half, you will also have to add 20-40% fuel to the cranking table in the hot fields, since IFR is off.

Kudos for figuring it out yourself. You might wanna try to bump it up some more.

[xc_SS/RS]

Originally Posted by Roader

Good writeup. We tried something similar to this before on my car and helped somewhat but always has a slow startup

Originally Posted by PepeLePew

Wow very thorough. Nice research and explanation! I love the seeing the data like this. If I am ever plagued by the non-starting issue when hot, I'll remember this.

Thanks! I noticed the starts got a little slower when I installed a smaller battery but it never seemed to fire right when warm. This helped a good bit

Originally Posted by eLeSthree

Cranking spark is something any decent tuner will change right off the bat even on just a cam tune.

Also, if you're running large injectors and you have doubled stoich and cut IFR in half, you will also have to add 20-40% fuel to the cranking table in the hot fields, since IFR is off.

Kudos for figuring it out yourself. You might wanna try to bump it up some more.

Thanks! It made a decent improvement but the two tuners I had didn't touch the table. Might be a SCT thing. Did not know that bit about adding larger injectors but I'll write it in my notes for when I move to e85