idle problem on new ls1 + hot cam
01-03-2010, 12:05 AM
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idle problem on new ls1 + hot cam ok, here is my problem, just installed a new ls1 with a hot cam,ls6 intake and a mail order fastchip pcm tune. car runs fantastic. however the idle is a bit erratic. It will hunt between 700 and 950rpm at idle then will settle in after about 30 seconds. It has a fairly consistent 750 to 850 rpm idle once its settled down. Then if you select ac, or if the fans are commanded on, it almost dies down to 400-500rpm and will once again start hunting with a 700 to 950 rpm surge. I have replaced the Iac valve and sprayed starting fluid all over lookking for a vacuum leak. It hasn't changed anything. I think if I had a vacuum leak I would have a consistent high idle. Any ideas?
01-03-2010, 08:56 AM
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You probably need more Idle Airflow. Unfortunately, you have to address that through the tuning software.
Note, there are many Idle Airflow Tables, and also tables that control Base Spark while at idle.
This is the toughest area to nail through a mail order tune. Unless they are very familiar with your cars fueling and airflow requirements..tough to do unless you have a lot of LS1 experience.
I would go through the vendor who did your tune. Otherwise, check with some of the Sponsors that frequent this site.
Good luck.
..WeathermanShawn..
Note, there are many Idle Airflow Tables, and also tables that control Base Spark while at idle.
This is the toughest area to nail through a mail order tune. Unless they are very familiar with your cars fueling and airflow requirements..tough to do unless you have a lot of LS1 experience.
I would go through the vendor who did your tune. Otherwise, check with some of the Sponsors that frequent this site.
Good luck.
..WeathermanShawn..
01-03-2010, 03:39 PM
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Mine does the same thing but, I have a Hot Cam with no tune. Mine does it about 5 to 10 seconds at startup and when I turn the ac on. It's like it takes the pcm a few seconds to adjust everything for the different cam then it straightens out.
01-04-2010, 12:13 PM
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Air probably isn't your problem. Just to be safe make sure the throttle position sensor is reading closed when the blades are actually closed. Everyone knows big cams don't really want to idle well, and getting them to do so requires some tweaking that you can't get with a mail order tune.
The way to get a big cam to idle well is to raise the idle speed. Then the tuner will richen the mixture to .9 lambda. Since there's a lot of reversion at idle some extra fuel is needed to ensure the cylinder has enough energy to power itself. Then timing is retarded in steps while lowering idle speed until you reach a point where the car idles well and cannot idle any slower, usually about 900rpm depending on the cam. The slightly rich mixture and less than ideal timing help to smooth the pressures inside they cylinder.
Long and short, it needs to see a doctor.
The way to get a big cam to idle well is to raise the idle speed. Then the tuner will richen the mixture to .9 lambda. Since there's a lot of reversion at idle some extra fuel is needed to ensure the cylinder has enough energy to power itself. Then timing is retarded in steps while lowering idle speed until you reach a point where the car idles well and cannot idle any slower, usually about 900rpm depending on the cam. The slightly rich mixture and less than ideal timing help to smooth the pressures inside they cylinder.
Long and short, it needs to see a doctor.
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01-04-2010, 04:34 PM
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Air probably isn't your problem. Just to be safe make sure the throttle position sensor is reading closed when the blades are actually closed. Everyone knows big cams don't really want to idle well, and getting them to do so requires some tweaking that you can't get with a mail order tune.
The way to get a big cam to idle well is to raise the idle speed. Then the tuner will richen the mixture to .9 lambda. Since there's a lot of reversion at idle some extra fuel is needed to ensure the cylinder has enough energy to power itself. Then timing is retarded in steps while lowering idle speed until you reach a point where the car idles well and cannot idle any slower, usually about 900rpm depending on the cam. The slightly rich mixture and less than ideal timing help to smooth the pressures inside they cylinder.
Long and short, it needs to see a doctor.
The way to get a big cam to idle well is to raise the idle speed. Then the tuner will richen the mixture to .9 lambda. Since there's a lot of reversion at idle some extra fuel is needed to ensure the cylinder has enough energy to power itself. Then timing is retarded in steps while lowering idle speed until you reach a point where the car idles well and cannot idle any slower, usually about 900rpm depending on the cam. The slightly rich mixture and less than ideal timing help to smooth the pressures inside they cylinder.
Long and short, it needs to see a doctor.
It is pretty hard to obtain .9 lambda in a today's closed-loop system. I am sure his tune is not open-loop. Mapping a fuel table without a wideband and logging is practically impossible. So, his tune will always trim to ~ 14.7 AFR regardless..which obtaining .9 lambda is not possible (unless SD tuned).
With today's tuning software, raising the idle is old-school. I and many others are running cam overlaps of 10+ degrees or higher, and mines purrs at 750 Rpm's (M6). Most big cams like an idle spark of ~22-28 degrees. The trick is getting the base timing to 'blend' with the High-Octane Sprak Tables, once you get moving.
To the OP, it is hard for a 'mail-order' tune to nail idle. If you look through enough threads, you will see quickly see which sponsors can set you up.
The GM Hot Cam is not difficult to tune, so good luck in getting it straightened out.
..WeathermanShawn..
01-05-2010, 11:47 PM
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well, fastchip advised me to check my iac counts and told me to adjust the idle stopscrew to a reading of 20 to 30. Before adjusting it read around 65. I turned the screw 3/4 of a turn in(opening the butterfly for more air) It now reads around 17 to 20. The idle seems more consistent now around 800. However it still hunts when I turn the air on. It will go from a stable idle to hunting between 500 and 900.
01-07-2010, 12:25 AM
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yep, no change. It seems fairly consistent and idles well till the air is selected on than its totally erratic. The tuner said to send the pcm back and he will dial in more air.
01-07-2010, 09:59 AM
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Remember, its kinda an educated guess that more Desired Idle Airflow is the culprit. Fueling and spark are contributers also, but hopefully your problem will be solved.
If that does not work, post again. There are several exceptional tuners on this board who also provide outstanding LS1 tuning services at a reasonable fee.
Good luck.
..WeathermanShawn..
01-07-2010, 10:23 AM
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Yeah, the good ol Hotcam - big cam idle, little cam
performance.
It has a pretty high overlap if I recall the specs. That
does two things. One, whacks your low end VE profile,
needing you to dress that area of the table. Two, lets
air blow through the valve overlap to spoof the O2
sensors to read lean, making rich closed loop.
Got to get the mixture right open loop first. Then, if
you are seeing a roughly sensible closed loop operation
but a skewed AFR, start bumping the O2 switchpoint
voltages (vs airflow mode) table to pick a voltage that
gives you a proper pivot AFR - bearing in mind that
14.7 "in the hole" is probably going to read leaner than
14.7 "in the pipe" owing to the shot-through air. If in
doubt, seek the lowest idle MAP as indicator of best
idle AFR.
performance.
It has a pretty high overlap if I recall the specs. That
does two things. One, whacks your low end VE profile,
needing you to dress that area of the table. Two, lets
air blow through the valve overlap to spoof the O2
sensors to read lean, making rich closed loop.
Got to get the mixture right open loop first. Then, if
you are seeing a roughly sensible closed loop operation
but a skewed AFR, start bumping the O2 switchpoint
voltages (vs airflow mode) table to pick a voltage that
gives you a proper pivot AFR - bearing in mind that
14.7 "in the hole" is probably going to read leaner than
14.7 "in the pipe" owing to the shot-through air. If in
doubt, seek the lowest idle MAP as indicator of best
idle AFR.
