Starting/ initial idle

[Robbieroflcopter]

Greetings,

I'm looking for a little help specific to my setup. I put an LS3 in my truck (NBS Silverado). It's running the cable throttle body with IAC. It's this engine: https://blueprintengines.com/collect...a368a5fe&_ss=c

So, it runs and drives pretty good. My only issue at this point is how it starts. Whether cold or hot it seems like it doesn't want to start/remain running. If I crank it it will catch and attempt to run, but at a reduced rpm (450 or so). It's really chugging along and struggling. It does this for about 10 seconds (if it can stay running this whole time- sometimes it does, sometimes it doesn't). At about the 10 or 12 second mark it revs up to about 1500 and then settles into a nice idle at around 775. Idles very well after this and runs/drives fine. While watching the datalog it seems like it is the ignition timing that causes the jump to 1500. The IAC seems to be the same (roughly) throughout this whole scenario. At about the 10 or 12 second mark it advances the timing and then idles up and is normal. Additionally, if I give it just a little gas while cranking it fires right up and jumps to about 1500 rpms. If I then let off the throttle slowly it will settle into an idle and run fine after that. I've not watched the timing while doing this type of start. Here's the tune and a log showing a few of these starts- a couple where it stays running and settles into a nice idle and a couple where it dies during the 10 seconds. It seems like the timing is consistently around the 4-6 mark when it is doing this chugging and then after it throws some timing at it the idle picks up and it runs fine.

Thanks for the help!

[Robbieroflcopter]

Greetings,

I'm looking for a little help specific to my setup. I put an LS3 in my truck (NBS Silverado). It's running the cable throttle body with IAC. It's this engine: https://blueprintengines.com/collect...a368a5fe&_ss=c

So, it runs and drives pretty good. My only issue at this point is how it starts. Whether cold or hot it seems like it doesn't want to start/remain running. If I crank it it will catch and attempt to run, but at a reduced rpm (450 or so). It's really chugging along and struggling. It does this for about 10 seconds (if it can stay running this whole time- sometimes it does, sometimes it doesn't). At about the 10 or 12 second mark it revs up to about 1500 and then settles into a nice idle at around 775. Idles very well after this and runs/drives fine. While watching the datalog it seems like it is the ignition timing that causes the jump to 1500. The IAC seems to be the same (roughly) throughout this whole scenario. At about the 10 or 12 second mark it advances the timing and then idles up and is normal. Additionally, if I give it just a little gas while cranking it fires right up and jumps to about 1500 rpms. If I then let off the throttle slowly it will settle into an idle and run fine after that. I've not watched the timing while doing this type of start. Here's the tune and a log showing a few of these starts- a couple where it stays running and settles into a nice idle and a couple where it dies during the 10 seconds. It seems like the timing is consistently around the 4-6 mark when it is doing this chugging and then after it throws some timing at it the idle picks up and it runs fine.

Thanks for the help!

OK, so I adjusted some things related to the timing during cranking. It started much better the last two times. It still has that weird surge after like 12 seconds but then settles down nicely. Can I throw more timing at it during the cranking? Here's the updated tune and log.

[Alvin]

I'm not convinced the IAC is actually working.

Use the scanner at an idle and move it from 0-128 (max in scanner) with that you should have several hundred RPM variance. 500+ RPM You can also try doing this while looking at the IAC motor removed.


A IAC motor runs into a stop on startup and then counts steps from there. If there is a issue like a bad coil in the IAC the IAC will not actually move. SO it thinks its moving.. its counting up but nothing is happening.

[Robbieroflcopter]

Greetings!

I'm convinced it's working because as I adjust the idle airflow in the tune it does change the idle. But also I can hear it. Cold start it's whistling like a son of a gun. When it warms up and says it's fully closed there's no noise. But, I will try this just to be sure. I am pretty new to this! Thank you for the advice and I will let you know.

[blindsquirrel]

Fully closed? It shouldn't ever fully close, that means there's too much air coming from somewhere else.

[Robbieroflcopter]

At hot idle it goes to 0 from time to time. But this is according to the scanner. I'm going to check that it's functioning per the previous response and I'll let you know. Idles great after I get past the 15 second mark. It's only the initial fire that's poor.

[blindsquirrel]

It should idle hot between, ideally, 40-60 counts. It should kill the engine if it ever closes all the way. If it doesn't, then there is too. much. air. coming from somewhere - either a vacuum leak, or the throttle stop screw needs adjusting.

[Robbieroflcopter]

I could never get it to start until I got it to where it is now. Does the tune look OK as far as spark and air/fuel?

[Robbieroflcopter]

I could never get it to start until I got it to where it is now. Does the tune look OK as far as spark and air/fuel?

So, the IAC is working. It raised the idle nearly 800 rpm when I maxed it. Also, with the changes I made yesterday the warm/hot starts are pretty good now. Idles right up to 800 and sticks! This morning, it took three attempts to cold start though. I'm thinking it either needs a little more timing during cranking or to crack the throttle body a bit more and reset the TPS? During my cold start this morning it did seem to be a little rich. Could that cause the problematic cold starting?

I am starting to respect those of you that have this whole tuning thing down. This stuff is complicated. And I'm starting from a tune where the big stuff has already been taken care of by a professional lol.

Here's the most recent tune that created this most recent log. Thanks again.

[blindsquirrel]

Do not open the throttle body more, it's already open too far if IAC ever goes to zero when it's running and it doesn't kill the engine. You need to follow the guide for setting up the TB and TPS and idle airflow.

[Robbieroflcopter]

I looked in the stickies and did not see the guide. If you happen to know where it's at would you mind linking it? As far as the position of the blade in the throttle body we got here after a bunch of trying to get it to start. When cold outside it would be at 310 and would not start without throttle. This was when I had the hot idle iac values between 40 and 60. So we cracked the throttle body, reset the tps and it started starting alot better. So, we did one more time and now it starts fairly consistently when colder and starts very well when warm. The way it is set now it still idles great when warm and even cold after those initial few seconds. And this is with the IAC below 20 and sometimes at 0. Not arguing with you, just providing context. I have no doubt that you know a bazillion times more about this than me lol.

Thanks again!

[Robbieroflcopter]

What would be the maximum advance for cranking? When it's up around 20 during a cold start it seems to rev right up to where it needs to be. Then the timing falls and it stumbles. For testing purposes, what's the maximum I could do to see if/how it affects the start?

[blindsquirrel]

https://forum.hptuners.com/showthrea...e-(w-pictures)

[awest623]

https://forum.hptuners.com/showthrea...e-(w-pictures)

I was about to post the same link.

For OP: follow that guide. It'll get your idle just about perfect.

[Robbieroflcopter]

I've pretty much followed that process via my tuner. And it idles great. Transitions are great now. We just couldn't get it to stay started after the initial fire. I watched the log and noticed that the timing was low after it fired so I adjusted those tables. It has fired every time and stayed running as well. Just curious what you all think about the tune and log. How much timing during cranking/idle is too much? I'm going to do the increase idle during timing thing this weekend to see what it likes as well. Certainly there are rules of thumb though- just curious what those are for idle/cranking timing!

I was about to post the same link.

For OP: follow that guide. It'll get your idle just about perfect.

[awest623]

Disclaimer: Most of my experience has been on tuning an l31 vortec, which is a gen 1 small block chevy. The tuning process is identical to gen 3 LS engines but the specifics (like ideal idle spark) are way different.

I've always just given her what she liked. If it cranks and idle good I wouldn't sweat it too much. Nothing looked dangerous in your original log, but it was definitely having some issues.

Go ahead and drop a new log file and I'll look at it, I'm sure some other people that have more experience on actual LS engines will too. That idle tuning process should have changed a lot of things including spark.

[awest623]

Remember I've never actually "tuned" and LS engine. But from what I've read, your idle spark should be AROUND 17-23 degrees. For cranking, the stock tables should work, adjust from there to find what it likes. Also remember your startup airflow (under the idle tab) plays a factor, and your startup VE (under the airflow tab). To get a good crank on my modified L31 I had to up the startup initial airflow and cranking VE.