67 Nova LQ9 help
02-03-2012, 05:30 PM
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67 Nova LQ9 help Hey guys, I really need some help. I am having some low speed issues with my car. The engine is a 2005 LQ9 I added a comp 220/224 112 cam, lsxrt manifold(stock injectors at 100%), headers and a 90 fast TB. The problem is when the car is at idle the engine wants to surge and it kinda "hunts" for a idle then flutters out and dies. I changed the 4l60e trans out for a t56 mag so I know it's not the convertor 
. I have had two pretty good tuners put this car on a dyno and tune it. It makes 410 hp and 409 Tq at the rear wheels. I just can't seem to get the low speed issues fixed. Heck, I even swapped the GM ecu out for a Holley hp and it still does the same thing. I'm thinking maybe a internal vacuum leak in the intake ? Camshaft retard problem? Any help? Thanks...
. I have had two pretty good tuners put this car on a dyno and tune it. It makes 410 hp and 409 Tq at the rear wheels. I just can't seem to get the low speed issues fixed. Heck, I even swapped the GM ecu out for a Holley hp and it still does the same thing. I'm thinking maybe a internal vacuum leak in the intake ? Camshaft retard problem? Any help? Thanks... 
02-05-2012, 08:00 PM
#4
Is it hunting when the car is in park/neutral? Or when you are coming to a stop? Did you check your TPS voltage/percentage?
Jon
PSI
Jon
PSI
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02-13-2012, 06:33 PM
#5
Found this on another forum,about the LSXRt manifold
I have found they are more difficult to tune, but most of the time its because people try to keep adding air to the cracker and follower tables. A lot of times, the surging is from a condition where there is TOO much airflow. When the PCM or ECM has a target idle speed to hit and the airflow commanded is too high, it has to resort to pulling timing to try to curb the overspeed condition and it can cause a buck-nasty surging effect that usually goes away upon coming to a full stop (at the same time the throttle cracker airflow is disabled). Yes they can be more involved to tune, but a good tuner can tame it for sure.
Also, on cabe driven setups, it is very important to mechanically introduce the additional airflow needed at idle for cam/head setups etc.. Using base airflow tables to obtain a stable idle will cause funky surges when driving. The IAC can only do so much. I like to leave the base airflow close to stock, add to the startup airflow tables and crack the blade open to obtain my target IAC count at idle. Once thats done and startup and P/N idling is good, then i'll work on drivability with the follower and cracker tables since they are only affecting airflow mostly when the vehicle is moving or when there is a rapid change in TPS. Alot of times, the cracker table can be reduced because you have manually increased airflow at closed throttle via the blade adjustment. Also have to make sure fuel and spark are optimum before airflow tuning.
I have found they are more difficult to tune, but most of the time its because people try to keep adding air to the cracker and follower tables. A lot of times, the surging is from a condition where there is TOO much airflow. When the PCM or ECM has a target idle speed to hit and the airflow commanded is too high, it has to resort to pulling timing to try to curb the overspeed condition and it can cause a buck-nasty surging effect that usually goes away upon coming to a full stop (at the same time the throttle cracker airflow is disabled). Yes they can be more involved to tune, but a good tuner can tame it for sure.
Also, on cabe driven setups, it is very important to mechanically introduce the additional airflow needed at idle for cam/head setups etc.. Using base airflow tables to obtain a stable idle will cause funky surges when driving. The IAC can only do so much. I like to leave the base airflow close to stock, add to the startup airflow tables and crack the blade open to obtain my target IAC count at idle. Once thats done and startup and P/N idling is good, then i'll work on drivability with the follower and cracker tables since they are only affecting airflow mostly when the vehicle is moving or when there is a rapid change in TPS. Alot of times, the cracker table can be reduced because you have manually increased airflow at closed throttle via the blade adjustment. Also have to make sure fuel and spark are optimum before airflow tuning.
