larger throttle body tuning

[THEFERMANATOR]

I tried searching, but I'm not coming up with an answer to my issue. I have a 99 TAHOE with a 5.7L vortec, 0411 PCM swap running an 02 OS, dual electric fans, Camaro segment swap(modified the request wire so it would cycle), marine intake, and a 454 throttle body. My issue is the original throttle body that came on a 5.7L is 75MM at the top, but necks down to 69MM just below the throttle blade, and the throttle blade has an airfoil on it that is almost a 1/2" tall on the blade itself. The 454 throttle body is a full 75MM straight through with no foil on the blade. My problem is GM cranks the IAC WAY open at low throttle positions to offset the foil on the blade, and with the larger throttle body I have a very touchy pedal because of all the IAC airflow. Running along at 40-45 it doesn't want to go into lockup or stay once in because I'm giving it so little throttle because of all the IAC airflow. You can watch it on the scanner crank the IAC open and it gets difficult to hold speeds below 50 because of it. I'm pretty sure it's throttle cracker and throttle follower I need to adjust(I've been comparing my values to those in a 5.7L LS and 5.3L truck), but I cannot find much info on tuning for this kind of issue, and I don't want to screw anything up. Any help is greatly appreciated.
This is what is currently loaded in it.
22986

[statesman]

Yep, way too much air in your cracker table and possibly a bit too much air in your follower table. The cracker table is a 'feel' table... there's no procedure for adjusting it, you just adjust until it feels right. Follower table can affect return to idle... but there's no published procedure to get this table right.

[turbo_bu]

One thing to try is to adjust the throttle body so that the IAC is not open as much. What is your IAC reading with a warm engine at idle?

As statesman said, all the idle tuning takes a bit to get it right.

[THEFERMANATOR]

I have it set now so that minimum air(IAC fully closed, hot idle of 200, & in park) is right around 450 RPM's. It adapts to 40 IAC steps at a hot idle in park, goes up to around 67 with the AC and fans on, and jumps another 8-10 steps when I put it in gear. One thing I've noticed is it will be setting around 72-75 steps idling in gear, as soon as I touch the throttle it jumps to 120-150 steps and jumps way up in RPM's. I tried cutting B4309 by 50% and it helped some, but not much. It still jumps up to 120 as soon as I start rolling, and goes to 200+ IAC steps if I give it any throttle to speak of(it used to go to 300+).

I also reduced the rolling idle to 750 from 800 trying to make it more driveable at slow speeds, but it still wants to idle at 800 as soon as I start moving. I also tried bumping the idle up from 550 to 575 in gear(to help the AC), but it returns to the 550 idle and slowly climbs back up to the 575 after I come to a complete stop. I'm going to try using the throttle follower and throttle cracker values from a 5.7l LS1 CAMARO tune file(similiar throttle body, MAF size, and displacement) and see how they work. I knew it was going to need some idle tuning for the different throttle body and intake, but I never would have guessed it needed this much. Guess I need to get my wideband, bite the bullet, and learn how to do gas tuning. Diesel tuning was SO much easier to figure out.

[SS2win]

Have you seen this --> https://forum.efilive.com/showthread.php?14439-Idle-Tips-amp-Tricks

[turbo_bu]

I am not 100% familiar with the throttle body you are using. Do you know how large the IAC passage is compared to the previous throttle body? There are some tables in there that define how much air the PCM "thinks" the IAC is flowing that may also need some adjusting.

[statesman]

Guess I need to get my wideband, bite the bullet, and learn how to do gas tuning.

Okay, that explains the state of your tune file. You really need to take your time and learn about gas engine tuning BEFORE you do any gas engine tuning. If you do insist on learning as you go, then at least make sure you log for Knock every time you do a log.

[THEFERMANATOR]

I am not 100% familiar with the throttle body you are using. Do you know how large the IAC passage is compared to the previous throttle body? There are some tables in there that define how much air the PCM "thinks" the IAC is flowing that may also need some adjusting.

The IAC passages are nearly identical between the 2 except the 454 throttle body has an extra passage, but it's blocked in my spacer(have to run one to clear the external fuel rail), and the intake. So it's just a empty void.


Okay, that explains the state of your tune file. You really need to take your time and learn about gas engine tuning BEFORE you do any gas engine tuning. If you do insist on learning as you go, then at least make sure you log for Knock every time you do a log.

I haven't made any changes so far other than turning off the EGR since the marine intake doesn't have provisions for one, changing the injector data, segment swap and fan settings, speedo corrections, and now trying to adjust for the different throttle body. The stock tuning for the 5.7l is this screwy because of how they designed the intake system. I know better than to make "tuning" changes without verifying AFR on a wideband.

All I'm trying to do right now is get it driveable with the marine intake on stock tuning with the electric fans before I start messing with fuel/timing.

What is throwing me is I've put the 75mm throttle body on a mild built 5.7l vortec before and we had none of these problems with the hyper sensitive throttle. I know others who have done these swaps have said the marine intake flows significantly better all across the board, I ported mine to get all the slag out and remove some goofy ramps they cast in before the injectors, so I can only guess that made it flow enough extra air it has created this touchy pedal.

i put in most of the throttle cracker and throttle follower data from an 02 LS1 Camaro and it's made it alot easier to control the throttle at low inputs, but it's still opening the IAC quite a bit trying to maintain roughly 10 lbs/min of theoretical flow through the IAC according to what my TECH 2 is telling me(I need to set up a PID list and do an actual data log on it still).

[Supercharged111]

So I never even considered this as a possibility for my TCC lockup woes in the dually. I still think it's an OS thing, or perhaps I haven't mimic'd my 1500 enough in the 3500, but probably some of my woes lie right here. I will tell you that, despite the 454 TB's size, it has progressive linkage whereas the 350 had linear linkage and that stupid lip which mimics progressive linkage. So foot inputs vs airflow were likely similar, but TP vs airflow was not. I can say that my lightly ported 350 TB fed that motor better than an 85mm does my 454 at low RPM attempted atmospheric airflow. Standing by for more education.

[statesman]

i put in most of the throttle cracker and throttle follower data from an 02 LS1 Camaro and it's made it alot easier to control the throttle at low inputs, but it's still opening the IAC quite a bit trying to maintain roughly 10 lbs/min of theoretical flow through the IAC according to what my TECH 2 is telling me(I need to set up a PID list and do an actual data log on it still).

Post your current tune file.

[statesman]

So I never even considered this as a possibility for my TCC lockup woes in the dually. I still think it's an OS thing, or perhaps I haven't mimic'd my 1500 enough in the 3500, but probably some of my woes lie right here.

Make sure that the road speed you log with SAE.VSS matches the speed displayed on your vehicle dash.

[THEFERMANATOR]

My throttle body is just the 454 throttle body and blade, I'm using the 350 shaft in it so the linkage hooks up like stock.

Here's my current file. The file I posted earlier is stock except for the EGR, injectors, fan settings, and corrected speedo/shift points. This one drives better, but I still need to dial it back some more, but it's at least driveable.
23000

[statesman]

Try this tune file. If it feels like it's still giving you too much air, then take a bit more out of the cracker. Also be aware that this is a spark ignition engine... the amount of spark advance in off-throttle situations will also affect how much deceleration you get.

[Supercharged111]

Make sure that the road speed you log with SAE.VSS matches the speed displayed on your vehicle dash.

I did set this with GPS observed speed at 70mph which is where I've calibrated my other vehicles. I figure 60-80 is where I'm most likely to get a ticket. Unless there's a way they can mismatch after a speedo cal? I'm back in log mode, will check.