Stalls when revs go down to idle
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From: Portland Oregon
Stalls when revs go down to idle LS3 with a 233/239 cam. Engine dies when I push in the clutch and lift off gas, or in neutral at a stop. It gets better after 30 minutes of driving. Idle is set at 1100. If I rev it to 2000, then let off, it will go all the way down to 500, stumble, cough, maybe find its way back to 1100. ... Once it finds 1100, it idles great. I have tried changing Throttle Cracker and Follower, but those don't help at 0 mph? I made some changes to Adaptive Idle, nothing seems to help, or change that drop to 500 and stall.
I have searched for days and read many threads. Is there a simple instruction on how to adjust for idle with this cam?
I have searched for days and read many threads. Is there a simple instruction on how to adjust for idle with this cam?
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Joined: Aug 2010
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From: Ann Arbor, MI
In my novice opinion, I see lots of problems:
1. The Idle Base Running Airflow table has mostly just the same value of 9.0. There is a relatively simple procedure for setting it exactly right at each different temp.
2. Your idle value of 1280 is ridiculously high for that cam. The idle routines cannot realistically reach it, especially with other mistakes here.
3. The "Min" values for the Adaptive Idle should be negative numbers; your are all positive which is basically disabling/confusing the Adapative Idle.
4. Your Idle Spark advance has an abrupt drop between .28 and .32, exactly in the area your engine is trying to idle. This area must be very smooth.
5. Your Idle Spark advance tables do not smoothly transition to the Main Spark Advance tables. So as you transition from Drive to Idle, you are loosing lots of advance.
6. The critical Spark -> Underspeed table is all zero'd out! The PCM can therefore not quickly boost the idle speed when it drops too low.
7. The Throttle Cracker and Throttle Follow tables are filled with identical values; this will not allow a smooth transition from Drive to Idle.
Sorry, but IMHO (and novice opinion) this is a badly hacked tune. I would suggest going back to the stock tune (this appears to be a '98 PCM), entering the Injector data, your current VE tables, increasing the stock values in the Base Airflow table by "3.0", increasing the idle speed to 950 and starting there. (I am forgetting a few steps here.)
Sorry, I don't have the link now, but there is a frequently referenced thread on the HPT forum on how to tune the idle of a high duration cam.
1. The Idle Base Running Airflow table has mostly just the same value of 9.0. There is a relatively simple procedure for setting it exactly right at each different temp.
2. Your idle value of 1280 is ridiculously high for that cam. The idle routines cannot realistically reach it, especially with other mistakes here.
3. The "Min" values for the Adaptive Idle should be negative numbers; your are all positive which is basically disabling/confusing the Adapative Idle.
4. Your Idle Spark advance has an abrupt drop between .28 and .32, exactly in the area your engine is trying to idle. This area must be very smooth.
5. Your Idle Spark advance tables do not smoothly transition to the Main Spark Advance tables. So as you transition from Drive to Idle, you are loosing lots of advance.
6. The critical Spark -> Underspeed table is all zero'd out! The PCM can therefore not quickly boost the idle speed when it drops too low.
7. The Throttle Cracker and Throttle Follow tables are filled with identical values; this will not allow a smooth transition from Drive to Idle.
Sorry, but IMHO (and novice opinion) this is a badly hacked tune. I would suggest going back to the stock tune (this appears to be a '98 PCM), entering the Injector data, your current VE tables, increasing the stock values in the Base Airflow table by "3.0", increasing the idle speed to 950 and starting there. (I am forgetting a few steps here.)
Sorry, I don't have the link now, but there is a frequently referenced thread on the HPT forum on how to tune the idle of a high duration cam.
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Joined: Aug 2004
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From: Portland Oregon
Thanks for looking at that tune. You are right, it is hacked. I searched to find the right way to set this, but only found bits of info, then started trial and error, mostly errors.
I will try to straighten it out, or go back, and record.
I will try to straighten it out, or go back, and record.
Thread Starter
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From: Portland Oregon
Mrvedit, your humble opinion turns out to be rocket science. Yes, All of that made a huge difference.
I added 3.0 to Base Running airflow. Most values are around 4.1 now.
Base idle RPM set to 1100, works well with this cam.
Adaptive Idle set to -.39 and +.55
Smoothed out idle spark tables.
Put 4.0 in the 0 cells of under speed Spark Table.
Throttle Cracker Airflow set to 3.5
Throttle follower set to .2999
Wow !! it actually idles. Doesn't die at stoplights. I have been working on my VE table and PE for years to make this car run. The idle was the last frontier. Thanks for your help.
Do my numbers look right?
I added 3.0 to Base Running airflow. Most values are around 4.1 now.
Base idle RPM set to 1100, works well with this cam.
Adaptive Idle set to -.39 and +.55
Smoothed out idle spark tables.
Put 4.0 in the 0 cells of under speed Spark Table.
Throttle Cracker Airflow set to 3.5
Throttle follower set to .2999
Wow !! it actually idles. Doesn't die at stoplights. I have been working on my VE table and PE for years to make this car run. The idle was the last frontier. Thanks for your help.
Do my numbers look right?
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From: Ann Arbor, MI
Glad it helped and your car running better now.
No, the values still don't look "right", just better.
First, when I said to add "3.0" to the Base Running Airflow, I assumed you were using units of g/sec, but it appears you are using Lb/min. In that case 4.1 is too high.
I don't have the link now, but there is a well documented procedure with a special HPT .cfg file for logging the correct airflow values and then just pasting them into the table.
Maybe someone else knows the link to the Base Airflow tuning procedure?
The Spark-> Underspeed table should have a smooth transition from about 10 degrees at -300rpm to 0 at 0 RPM. I use slightly larger values for that table.
14.0, 12.0, 10.0, 8.0, 6.0, 4.0, 3.0, 2.0, 1.0, 0.0
Throttle Cracker and Follower are much more complex tables; look at the stock one.
I am still learning how to use/mod these tables; hence I am still a "novice".
No, the values still don't look "right", just better.
First, when I said to add "3.0" to the Base Running Airflow, I assumed you were using units of g/sec, but it appears you are using Lb/min. In that case 4.1 is too high.
I don't have the link now, but there is a well documented procedure with a special HPT .cfg file for logging the correct airflow values and then just pasting them into the table.
Maybe someone else knows the link to the Base Airflow tuning procedure?
The Spark-> Underspeed table should have a smooth transition from about 10 degrees at -300rpm to 0 at 0 RPM. I use slightly larger values for that table.
14.0, 12.0, 10.0, 8.0, 6.0, 4.0, 3.0, 2.0, 1.0, 0.0
Throttle Cracker and Follower are much more complex tables; look at the stock one.
I am still learning how to use/mod these tables; hence I am still a "novice".
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Verdad Gallardo Moderator
Joined: Aug 2010
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From: Ann Arbor, MI
Those are exactly the two widely used threads on the HPT forum that describe how the idle correctly after a cam swap. They will solve 90% of the "My cam'ed car won't idle" problems.
I now wonder if there are any good threads on how to tune the Throttle Cracker and Throttle Follower tables.
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From: Monroe,NY
I never found any great articles on cracker or follower. But I scanned both while driving and then made changes that way. For my 1999 truck pcm throttle cracker was the one being used when letting off throttle coming to a stop. The higher the #s the iac opens more and will cause the cruise control feel.
Thread Starter
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Joined: Aug 2004
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From: Portland Oregon
It just keeps getting better. Only one question now. Adaptive Idle Airflow Has Max in Gear, Min In Gear, I have set to .55 lb/min and -.39
----- Max P/N, Min P/N is set at 0.
Should there be values in these cells?
----- Max P/N, Min P/N is set at 0.
Should there be values in these cells?