jvanderwall

For those that don't know, this is a continuation from a previous thread. KAWABUGGY asked that I log a set of parameters and tune the idle by watching the RUSSK video. I haven't had much time in the garage, but I did run a log while the motor was still relatively "cold" (84 degrees). I did not tune the idle yet, but I understand how to do so from the video:
Currently, the motor will start with a little help opening the throttle cable. It will not start cold without help. If you let go of the throttle cable, then the motor dies (when cold). As the motor starts to warm up, it can be restarted without help from the throttle cable, it will also continue to idle without help.

I made changes to the intake and understand that I will have to tune the idle, but I wanted to post this and see if the experts in this thread can make anything out from the log I did perform. Give me your thoughts. Thank you.

When I logged the channels, the following actions were performed.

1) Tried to start once
2) Tried to start twice
3) Tried to start thrice
4) Tried to start with 3% help from throttle cable
5) STARTED with above 3% help from throttle cable
6) The throttle cable was held open to keep the motor running around 1500RPM and then slowly let down to idle around 700RPM
7) Allow motor to idle
8) Pull throttle cable to rev motor to 2000RPM
9) Allow motor to idle
10) Pull throttle cable to rev motor to 2000 RPM
11) Allow motor to idle
12) Pull throttle cable to rev motor to 2000RPM
13) Allow motor to idle
14) SHUTDOWN

Haggar

I didn't see the other thread, and can't watch the video here on my work PC. What cam do you have again? But, for me and idle tuning/start tuning my 2 DBC cars, here are the 3 things I have needed to mess with:

1) Throttle body open position. I think that you would have covered with that RussK technique. For my Holley systems, I just go by what I saw from Sloppy Mechanics: When it felt choked for air, I increased it until it read 3% on the IAC, then did an IAC reset. I had to do that 2 or 3 times on my 403 with a 102mm tb and a 239/247 cam.

2) Bigger cams are less efficient at low rpm... so they need less fuel at low rpms, so often leaning them out is required for starting/idling.

3) Due to point #2, they also may need a little more ignition advance in the idle area. The area below the idle area should get even more advance, so that if its well below target, that helps give an extra kick to get it back into higher rpm.

Looking in your log files.. the failed starts were in the range of 17-18 degrees, the one that started was into the 20s, then once it caught, it was into the 40s in ignition advance.

Have you tried setting your target idle higher, like 900, and work from there? Get it to start and idle, then work settings backwards until you get back down to your actual desired idle.

gagliano7

Does your LM7 have a cam or any other mods?

jvanderwall

Haggar and gagliano7, thanks for your reply.

Here is a link to the other thread: https://ls1tech.com/forums/conversio...l#post20459532

This is a stock 2000 5.3 GEN III LM7 DBC. The computer came with the motor out of the same vehicle - a Yukon.

- The only adjustments made to the computer were to remove VATS.
- The only adjustment made to the motor was opening the butterfly adjustment screw a little to get it to start on its own. After making this adjustment, the motor starts cold, but when it warms up, it will start loping and can't hold a steady idle. I have since attempted to put the butterfly adjustment screw back to stock. Now it won't start cold, but when it warms up (by starting with throttle), it will idle in the target range from the tables (~700RPM)

How do you reset the IAC?

Answering your question from 3), I haven't made any changes to the tune for this motor since I've only watched one video on tuning the idle. If we can determine all looks good from the log I posted, I will adjust the advance and increase idle RPM to get it to idle right.

I just really want to get the butterfly back in it's original position before I start tuning the motor. I would like to understand more about "IAC counts". How to I get this dialed back in?

gagliano7

You want your iac count about 30-60 count but can be a little higher. The throttle body has a set screw you can adjust but everytime you adjust it you need to do a tps reset. Being stock you shouldn't need any adjustments. Are you sure you don't have a vacuum leak.

TPS reset after you make adjustments
https://ls1tech.com/forums/pcm-diagn...ter-reset.html

jvanderwall

That's exactly what I thought when this initially happened. I haven't found a vacuum leak. The thing should definitely start though!