Gen IV E38 PCM Airflow tuning - Yellow Bullet Forums

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Old 06-06-2013, 06:37 PM   #1
TrikeMike
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Default Gen IV E38 PCM Airflow tuning

Was wondering if you guys had any insight on Idle Airflow tuning on a Gen IV LS vehicle equipped with Electronic Throttle. It seems that no matter what changes I make to any of the idle airflow tables or throttle tables I cannot get this vehicle to idle with the A/C on and it wants to die coming to a stop.

The truck has a bone stock 5.3 with 72lb injectors and a 2bar map sensor. It has a 76mm t4 turbo, I believe the KB racing kit. I am using HPtuners with the 2bar custom OS. The VE table is dialed in, drives fine, STFTs are all dialed in, WOT AFR error is dialed in as well. Vehicle is pretty much done aside from the idle airflow stuff. I read a how to "Bills idle tuning" but it still doesn't get me to where I need to be. When you command idle up in the VCM controls anything over 800 or so it will not go up, timing goes up to 30*+ advance to try to keep engine running but it seems the throttle will not crack open anymore like I want it to. This is the first Gen IV I've done and I appreciate any ideas or help. Thank you.
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Old 06-06-2013, 09:53 PM   #2
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Default Re: Gen IV E38 PCM Airflow tuning

ok they are a simple beast, depending on your cam you may need a hole in the TB to make it work correctly, start off at 1/8", you need to keep the idle TPS at close to stock or you will have all sorts of problems,

what is your idle TPS %?
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Old 06-06-2013, 10:18 PM   #3
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Default Re: Gen IV E38 PCM Airflow tuning

It is a Drive By Wire electronic throttle body with a stock cam so I do not want to drill a hole. ETC Position at idle is about 15% when it wont go up higher in idle RPM.
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Old 06-06-2013, 10:19 PM   #4
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Default Re: Gen IV E38 PCM Airflow tuning

ok stock cam makes it a little strange... post the tune file
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Old 06-06-2013, 11:42 PM   #5
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Default Re: Gen IV E38 PCM Airflow tuning

Quote:
Originally Posted by 10sec_rx7 View Post
ok they are a simple beast, depending on your cam you may need a hole in the TB to make it work correctly, start off at 1/8", you need to keep the idle TPS at close to stock or you will have all sorts of problems,

what is your idle TPS %?
Drilling the tb is the wrong way to do it.
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Old 06-07-2013, 12:02 AM   #6
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Default Re: Gen IV E38 PCM Airflow tuning

You don't want to drill holes. You need to adjust your idle airflow table.
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Old 06-07-2013, 01:17 AM   #7
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Default Re: Gen IV E38 PCM Airflow tuning

Turn your idle timing down, then crank in base running airflow to bring idle back up. The lower timing allows the idle timing to function correctly because now when it adds timing, it can actually raise idle from having more torque.

You may need to change the coast down table as well as the main ign map.
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Old 06-07-2013, 01:27 AM   #8
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Default Re: Gen IV E38 PCM Airflow tuning

Quote:
Originally Posted by minytrker View Post
Drilling the tb is the wrong way to do it.
I assumed it had a big cam in it... if you have a big cam the best way is to give the engine a small hole to get it to work as when your idle throttle % gets too high it fucks with a lot of things..
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Old 06-07-2013, 01:30 AM   #9
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Default Re: Gen IV E38 PCM Airflow tuning

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Originally Posted by 10sec_rx7 View Post
I assumed it had a big cam in it... if you have a big cam the best way is to give the engine a small hole to get it to work as when your idle throttle % gets too high it fucks with a lot of things..
110% correct. Like fueling. It correlates TPS and associates a fuel quantity with it.

In theory, you can tune it with out drilling a hole. And you can, with a mechanical TB.

Drive by wire, if you think you can tune idle correctly with light weight rotating assembly, big injectors and a small clutch, with out the potential of drilling a hole, you're hugely mistaken.
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Old 06-07-2013, 01:31 AM   #10
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Default Re: Gen IV E38 PCM Airflow tuning

I don't have any real way of posting the tune at the moment but all the air flow tables are stock E38 truck PCM for an 08 Suburban. I understand airflow and have tuned gen 3 stuff before but it seems that no matter what I do in the airflow tables it still doesn't make a difference.
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Old 06-07-2013, 01:33 AM   #11
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Default Re: Gen IV E38 PCM Airflow tuning

Turn idle timing down, needs to be in the 6-13* range.

In the idle tab, go to base idle or base running airflow, and multiply the table by 1.5, and see what it does. Might be 25% more, might be twice more. I'm just shooting off the hip.

You can email me a log and the file too, if you want. Louisgigliotti at yahoo.com
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Old 06-07-2013, 01:34 AM   #12
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Default Re: Gen IV E38 PCM Airflow tuning

Like I can multiply the airflow tables anywhere from 5% to 50% and it doesn't seem to help much.
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Old 06-07-2013, 01:34 AM   #13
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Default Re: Gen IV E38 PCM Airflow tuning

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Originally Posted by Louis G View Post
Turn idle timing down, needs to be in the 6-13* range.

In the idle tab, go to base idle or base running airflow, and multiply the table by 1.5, and see what it does. Might be 25% more, might be twice more. I'm just shooting off the hip.

You can email me a log and the file too, if you want. Louisgigliotti at yahoo.com
Thanks will give it a try tomorrow I appreciate the help everyone.
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Old 06-07-2013, 01:35 AM   #14
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Default Re: Gen IV E38 PCM Airflow tuning

Lean out the idle areas of the map then and turn off trims there. 14.5-15.5ish AFR.
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Old 06-07-2013, 06:16 PM   #15
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Default Re: Gen IV E38 PCM Airflow tuning

Quote:
Originally Posted by 10sec_rx7 View Post
I assumed it had a big cam in it... if you have a big cam the best way is to give the engine a small hole to get it to work as when your idle throttle % gets too high it fucks with a lot of things..
Guess there's more than one way to achieve the same results. I never drilled any TB's in last 10 years. I have seen many TB's with to big a hole over the years so I never got into drilling them.
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