Year, Make, and Model: 2004 Pontiac GTO
Engine and Trans: 5.7, 4l60
Fuel: 91 Octane
Modifications: Torquer V3 Cam, dual springs, stock tb, 3500 stall, 3.90 gears, ABS Delete
Back story: Bud bought this GTO at 5k miles. About 3 years ago, he had some modifications done at a shop in our region and then tuned. It hasn't quite been right since. We hope to have him loving this car even more now.
- Stumbling / dying when coming to a stop, more pronounced when cold, and during a 2-1 shift
- Erratic Idle speed. Higher than desired, poor sound quality
- Adaptive idle non-functional, preventing the ECU from hitting target idle speeds
- Incorrect Speedometer calibration, after 3.90 gear swap
- Shift points less than optimal for performance-oriented driving
- Poor calibration of airflow measurement
- Poor calibration of fueling needs
- Poor calibration of ignition timing
- Many ancillary parameters modified that did not need to be changed
In order to resolve the above concerns, we had to modify a total of 116 parameters / tables. There were a number of changes to the calibration that did not make sense, as the factory values were more appropriate. For the most part, we had to start over with an OEM calibration from another 2004 GTO in order to get the drivability we expected out of this vehicle.
Above: VE Tables, used for airflow and fueling calculations… OLD vs NEW. You shouldn’t have values going up and down and up and down in a single row… We removed 2-15% at low load areas, and added 6-9% at high load, based on data from our wide-band o2 sensor.
It looks like the previous tuner only modified the cells that he was able to hit on a dyno. The outlying cells at the bottom weren’t adjusted to reflect the slope of the rest of the VE table. Should you have hit these un-tuned cells in real world driving on the street, the car would be rich and stumble.
Often when tuning, you record incorrect data for a cell that you do not cross over frequently. When using raw data for corrections, this can lead to the stair-step appearance that you see in the middle of the old VE table.
The sharp cliff at the top of the old VE table (Between 95 and 100kpa) is also concerning:
Should you have good atmospheric conditions at WOT, you’ll hit around 100kpa… At 6000rpm, and 100kpa, the ECU calculates a VE of 105. If you ended up with an elevation change, or lower barometric pressure, your manifold air pressure could easily hit 95kpa. In this situation, your VE would calculate to 95, which is 10% leaner than target.
Our new VE table has a more appropriate slope in the WOT area for more consistent fueling:
Above: High Octane Timing table. OLD vs NEW… I don’t really know where to start with this… There are a lot of bad things about this table; primarily the quantity of timing the GTO was running. At full load, it commanded 28* of timing at peak torque, sloping down to 27* on the shift. When cylinder pressure is the highest (peak torque), you don’t need as much timing. We are now at 23* at peak torque, ramping up to 26* at the shift.
Above: This is the OLD Power Enrich table, which defines how much fuel the GTO needs under a high load / WOT condition. It is expressed in Equivalency (EQ) ratio.
An EQ ratio of 1 is “Stoichiometric”, a complete burn of air and fuel with nothing left over.
For gasoline, that’s a ratio of 14.7-parts air to 1-part fuel (14.7:1)… An EQ ratio of 1.349 means there will be 34.9% extra fuel (Rich). That comes out to an air fuel ratio of 10.8:1. You wouldn’t want to run this motor at that rich of an AFR even if it were boosted.
Our calibration is commanding an EQ of 1.195, which is an AFR of 12.3:1… This results in a measured wide-open-throttle air fuel ratio of 12.7:1 in 1st gear, 12.5:1 in 2nd gear, and 12.3:1 in 3rd gear.
- Cylinder Volume (displacement) parameter was changed; Should not have been.
- A shift-light was commanded at 7000. This doesn’t make sense on an auto that shifts at 6300
- Target idle speed was configured poorly…. Especially at 46*f… Columns represent coolant temp:
- Idle adapts, IAC settings, Airflow, Fan load, Throttle follower were all modified when the previous tuner was trying to get the GTO to idle properly... Correctly calibrating the Base Running Airflow as well as Startup airflow allowed for clean starts
- Throttle Cracker has now been disabled. It was too aggressive even at low airflow values.
- Primary VE and MAF are now tuned with data from a wideband in the front driver’s o2 sensor bung. The other three o2 sensors were torqued excessively and did not want to come out
- Returned Dynamic Airflow Filter Coefficient to factory
- Returned Cranking to Run time to factory
- Returned Dynamic Airflow Steady State Idle to factory
- Returned Throttle Max Rotation % vs RPM to factory
- Fuel Injector flow rate was changed in a few cells by a couple %. This really shouldn’t be done, as it does not reflect actual injector data, and throws off VE and MAF values
- Long Term Fuel Trim configuration was returned to stock. It was modified inappropriately
- Power Enrich (Extra fuel when you’re accelerating hard) was not coming on at part throttle because the calibration was set to look for the engine to make “100%” torque before entering PE
- Power Enrich Values were wildly inappropriate for this vehicle
- Cutoff (Limiter) is now reduced from 6700 to 6500
- Deceleration Fuel Cutoff (You don’t need to inject fuel when you are decelerating in gear) is turned back on
- Idle Spark vs Main Spark criteria had been modified. I returned this to stock
- Intake Air Temp spark correction needed repaired. It was configured to pull a flat 5* of timing (which is a lot) as soon as the intake air temp sensor gets to 122*F
- Startup and Cranking ignition settings were returned to factory
- Over and Under speed timing control was modified to better suit the profile of the cam
- Knock retard settings were returned to factory (They were turned down)
- Burst Knock (Anticipated knock) is now turned off, as it isn’t needed in this application
- Maximum Torque vs RPM returned to factory (This is not a limit)
- Maximum Net Engine Torque returned to factory (This should not be modified on a GTO)
- ETC TPS Max vs RPM vs % Max Available Torque returned to factory (This is not a limit)
- Spark Retard vs Torque Reduction was set to more appropriate values than “Off”
- Traction Control Spark Retard was set to more appropriate values than “Off”
- Drivetrain Abuse was disabled (Previous enabled any time above 2000rpm)
- VATS Disabled (Anti-Theft P1632 was cutting the fuel after startup)
- Second stage fan set to turn on at 210*f rather than 235*f
- Speedometer calibration corrected for actual tire size and gears
- Transmission Desired Torque returned to factory
- Transmission torque management adjusted so that it is less intrusive when at part throttle
- Shift points raised to accommodate torque converter’s higher stall speed
- Shift points set to ramp in more aggressively towards 25% throttle and up
This GTO has been great to work with. I doubt we'll see one as clean as this anytime soon. I love the way the cam sounds, and the car has the power to match. Projects like this are a lot of fun, because you get to turn a mess of a calibration into something that works and can be relied upon for many years to come.