Quote:
Originally Posted by ps2fixer
I think the car is going into lockup fine since it shifts 4 times (4 speed) and has another spot that feels like another gear (lockup). It is doing about the same RPM in both good mpg vs not so good and going faster, say 50mph or 55 does not show better mpg but worse.
I need to check the idle IGN readings, I think it is around 8-12.
I talked to an engeneer today about this since he had pc issues (i'm a computer tech), and he thinks it is the knock sensor.
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Yes, I realized that it would feel like that, - that the converter had already locked. The purpose of the PWM strategy (which is based on engine loading by the way) is to make the TCC function less perceptible to the driver.
Also, due to the function of the PWM, you will not see such a clear change in engine RPM at certain loads. This is exactly why the PWM strategy makes the function smoother in terms of driver perception. That's why I suggested a test to rule this out, or confirm.
Most scan/datalogging software will show you the TCC function flag (on or off) and some will show the duty cycle as well.
Speaking of knock sensors, that same scan/datalogging software will show you knock sensor output in a term called "knock counts", or "knock retard", - the retard being the result of the adaptive spark logic in the PCM.
One more thing to check is your EGR function if your car has a PCM controlled EGR valve. Again there are two strategies for EGR function: either on/off, or a PWM or stepper-motor controlled solenoid that delivers based on a calculated duty cycle. When EGR function is active, the spark advance is increased. When you fall below the thresholds for EGR operation (different for different PCM/calibrations), then the spark advance will drop, - usually in the neighborhood of 10*.
The EGR delivery decreases combustion efficiency, hence the need to start the spark sooner, so depending on engine loading & conditions it will definitely affect your fuel mileage.
The SG2 will often report EGR duty cycle on many models once you add it via x-gauge.
All of these (TCC, KR, and EGR) are based on variations in engine loading, so their effects will be noticeable as you change loading by backing off of the throttle while driving.
Given your curiosity about this sort of thing, it sounds like you would be a lot happier if you invested in one of those scan/datalogging smart-phone apps so that you could monitor what exactly is going on in your car. All you would need extra is a Y-cable (one male end plug, and two female plugs) for the ALDL port.
There are other more sophisticated datalogging software that will display the reported data in optional units, and ranges of resolution. For example instead of seeing your throttle position as 15%, you could have it display as 15.34%. This sort of thing comes in handy when working towards higher MPG.
Using the same method (some software will show instant MPG or fuel consumption), you could have your instant fuel economy reported to several extra decimal places in order to monitor very small changes in a narrow range of test conditions.