Overkill Performance PCM Tuning
Thank you for purchasing the Overkill PCM, a product of extensive research and development from a 3800 enthusiast to make your supercharged 3800 engines more fun to drive.
This outline is to provide you with a detailed description of what enhancements have been made within the programming and what to expect behind the wheel.
Key Features:
-Performance fueling specifically for smaller supercharger pulleys
-Reduced spark retard (KR). Timing advance optimized for power and KR reduction.
-Lower operating temperatures - fan settings calibrated for 180* thermostat
-Speed Limiters removed and Rev Limiters raised
-Performance-Shift shift patterns remapped for true sport feel
- Redline full throttle shifts
- Delayed upshifts
- More responsive downshifts
- Highway 4-2 skip-shift enabled
- Overdrive bogging reduced/eliminated
- Increased line pressure for more responsive shifts
-Will not affect emissions testing
-Hazardous “Torque Management” retuned
-Custom tuning for your car’s specific modifications
Please Note: Due to the personalized nature of aftermarket performance modifications, the end user must accept all liabilities for the use of this PCM in their car. Each car’s owner and setup is different and may react differently to the same modifications as others, thus no guarantees can be made in every application. This guideline may be used by the end user to judge the fitness of this PCM for their application before use. A scan of your vehicle after installation is highly recommended. We are here to help you, so please email us at
FAQ
I’ve just installed my PCM, what should I do first?
The first thing that should be done is to start the vehicle and ensure proper operation. The initial startup will take longer than normal, the signature GM quickstarting will return once the PCM has gone through its relearn procedures.
Ensure that your vehicle does not require a security relearn procedure, some 2001-2002 models may require this. We have changed the relearn requirements from three 10 minute cycles to one 5 second cycle. To perform this, simple close the doors, use your non-valet key to turn the ignition to the on position, wait for 5 seconds after the chimes, turn the key off, wait for 10 seconds, and then start the vehicle.
Drive around the block under mild acceleration. Feel the transmission gearchanges and feel for any hesitations, ensure the vehicle feels normal to you.
It is highly recommended that your vehicle be scanned after the installation of this computer. If you do not own a scantool, such as an autotap, then bribe a local car enthusiast that does have one with soda and sandwiches to scan your vehicle with you.
Drive the vehicle normally for the first 10-15 minutes to let the computer do an initial relearn, it will take several days to fully learn. When you start to push the accelerator further, keep an eye on the KR, O2 values and other data and back off the throttle at and signs of danger.
Play with some of the difference settings, like normal and performance shift, and try and get used to the change in feel of the vehicle, so that you don’t discover a hidden feature of this PCM months down the road and worry whether it is normal or not.
How do I scan the vehicle? What parameters should I scan? What do they mean?
You will need a scantool device or software, such as Autotap or LS1-m. If you don’t have one, you’ll need to find someone who does if you want to scan the car. Your local garage will normally not have the scanners necessary, unless they have a handheld Snap-on scanner and are willing to go for a boot with you.
Unfortunately this guideline can’t provide technical support of your scantools as they all vary in operation. You will need to contact its creator for instructions of operation.
If you wish to send a scan to Overkill for feedback, scan the following parameters:
-LT fuel trims
-ST fuel trims
-RPM
-MPH
-TPS %
-Spark Advance
-Knock Retard
-B1S1 O2 voltage
-MAP in KPA
-MAFF frequency in htz
What should the parameters say, what readings are normal?
Watch your LT fuel trims at part throttle. We'd like to see those as close to zero as possible, but positive or negative 5 and within is very acceptable. If these settings are out, ensure that you have no vacuum leaks, flush your injectors if it's been a while with some injector cleaner, and clean your MAF sensor.
As you push the vehicle to a half throttle, monitor your KR for any signs of danger. These should be as zero as possible. As you go full throttle, up to 4 degrees of KR is within a reasonabley acceptable range, anything higher and proceed with caution.
At a half throttle, your B1S1 O2 readings should start to lock in to values between 850-1000. They will jump around when you are at cruising or idle, this is entirely normal. At half throttle, your O2s should start around 870 and climb to 910-920 O2s. At full throttle, these values should lock into 930-950.
Will I need a CASE relearn?
Only if your vehicle tells you you need one. It will throw an SES light, telling you to perform one if it requires one. You will need to go to a GM dealership to have this performed.
Will this program affect my ability to pass emissions?
In most circumstances, no. It has been shown that on occasion, on vehicles that are “borderline” on their emissions output, that the increased timing advance offered by any aftermarket PCM may cause a further elevation in readings, particularly Nox readings. We are however the only PCM tuner that offers a solution; by unplugging your IAT sensor, your timing advance will return to near stock levels, better enabling you to pass your e-test. It is recommended that you unplug this sensor for your test, regardless of whether you feel your vehicle will have trouble.
Will my gas mileage be affected?
This will highly depend on your driving style. Under light throttle and cruise, your gas mileage should improve. Under moderate to heavy acceleration, your mileage will decrease due to the additional fueling for performance and engine safety with increased boost. Reports of 30+MPG on highway trips are not uncommon, however it is up to you to operate the vehicle in a fuel conscientious way.
The stock computer is tuned for emissions and mileage friendly operation by introducing performance fueling very late in the throttle travel. This means you may still be aiming for a very lean air fuel ratio while developing a lot of boost at part throttle, this is very dangerous! The Overkill PCM introduces performance
fueling sooner in the throttle travel, this provides more power, smoother power and responsiveness, and much safer engine operation, at the expensive of a little gas mileage. So for best mileage, stay below 1/3 throttle.
Must I run high octane gas with this PCM?
YES! You must run the HIGHEST octane you can find with this PCM, 91 is a minimal but Sunoco 94 is recommended wherever available. You should be running the highest octane available with any modified GTP for performance and engine safety.
What horsepower gains can be expected from this PCM?
The gains of the PCM will vary from car to car based on its modifications, anywhere from 10-30 horsepower or more. A proper computer tune will unlock power that already exists in your car, and increase it to its best capabilities based on your selection of modifications and mechanical condition.
Is this PCM harder on my engine or transmission?
This PCM is actually safer on your engine than remaining with a stock PCM. When increasing boost, it is vital to match it with proper fueling to prevent the engine from running lean which can lead to performance loss and engine damage. This PCM keeps the engine properly fueled. Your engine will rev to near redline at full throttle shifts in performance shift, this is the only feature that may decrease the life expectancy of your engine, using a good engine oil and changing it regularly is highly recommended.
This PCM is not harder on your transmission. The shifting is quicker but not abrupt which minimizes wear and tear that soft shifts can cause on clutches and hard shifts can do on hard metal parts in the transmission. In performance mode, the transmission will be more eager to switch gears back and forth, in doing so this simple act of shifting gears often may cause a decrease in life expectancy, however since the transmission is keeping itself in a lower gear and decreasing
the strain it feels from high engine load in higher gears which increases life expectancy on converters and clutches, there is a balancing effect.
Technical FAQ
What changes have been made to fueling over a stock or other aftermarket PCM?
The Overkill PCM boasts proprietary fueling enhancements to the following:
-Fueling has been skewed between different cylinders, offering those more prone to pre-ignition and those closer to the supercharger outlet more fuel for lower KR
-Performance fueling has been activated sooner in the throttle travel, to accompany the increased boost at lower throttle levels with proper fueling. This feature is further enhanced with fuel alterations based on throttle position; the engine’s fueling will increase the further the throttle is pushed down, rather than fueling 1/3 throttle the same as full throttle
-Fueling based on time at full throttle is designed to increase fuel the longer you are at full throttle, to decrease KR on highway runs and increase acceleration throughout each progressive gear
-Burst fueling is highly revised to provide more fuel on quick throttle tipins to control burst KR on the highway.
Overall, the Overkill PCM is set to run more towards the rich side of normal at WOT. A well fueled motor is a safe and happy motor, much less likely to cause engine damage from detonation, and running well fueled has a KR decreasing effect on most cars. You will see less KR on your car resulting in more horsepower. Normal O2 values will fall anywhere from 930-960 depending on the year of your car, your type of power adder and whether your forced induction is intercooled or not. You should see 11.0-11.3 on a wideband O2 sensor when tuning on the street (not a dynojet)
What about spark advance, what should I see at full throttle, and what changes are made to the knock retard tables, are they less sensitive to engine knock?
The timing advance table in this PCM is highly modified over stock. It is designed to increase spark where allowable and decrease spark in trouble areas that cause part throttle knock retard. At full throttle, your timing advance will not exceed 17-18* degrees advance with zero knock retard. 17* is an increase of 1-3* over stock and optimal for making good power while keeping the motor safe.
In no way has knock retard been discouraged from being initialized, infact its been further encouraged. The Overkill PCM will institute more KR to counter the same amount of pre-ignition the knock sensors hear compared to factory, both in its quickness and in amount. Knock retard is a friend to the engine, keeping it out of harm’s way; it is important to have KR despite it meaning a loss in performance when it is instituted. Remember that KR is not bad; the reason KR is being used is what is bad. To counter the quicker KR institution rates, knock retard recovery rates are also increased over stock. When your motor does detonate for only a brief moment, it recovers from it much more quickly and is able to bring back full timing advance and full power back sooner. KR recovery settings are twice as fast as most competitors, and 10x as fast as a factory PCM.
Another special feature of the Overkill PCM is that it has been shown that knock retard is often linked to hot air being drawn in from the air intake system. Heat is the cause of detonation and knock retard, and its journey starts with the air inlet temperatures. Some have removed air inlet restrictions by placing an open cone under the hood while others have bought or built what they believe are cold air intakes, this results in intake temperatures anywhere from 15-50*C above ambient temperatures! The Overkill PCM is smart and uses the sensor for intake air temperatures already existing on your car to monitor the incoming air temperature and will start to decrease timing advance based on how hot the air entering the engine is. This decreases the likelihood of increased detonation resulting from a hot air intake and is good inspiration to review your choice of performance intake setups!
Why run the motor cooler with a 160 or 180 thermostat? Which is best to use?
A cooler running motor is less likely to detonate and will provide more consistent performance than one which is being run extremely hot to provide the best emissions results, such as with a factory PCM. A 180 is recommended for most cars, as it is friendlier for year round performance and still retains good mileage and performance on a daily driven car.
The fan settings will be programmed for each as follows:
-Low speed fans will turn on at the thermostat temperature, this means whenever coolant starts flowing from the engine through the radiator, the fans are cooling it. Low speed fans will turn off at speeds above 40mph when the airflow through the radiator due to the speed of the vehicle is sufficient to cool the car without the low speed fan’s help