torque converter - Q

[Grabber523]

Originally Posted by JackandJanet

Good information Grabber, thanks! This also makes me think it's not a good idea to "continuously" run in WOT (even though I know you really can't). But, people who continuously like to drop the hammer are going to be in that open loop mode probably more than is good for the engine.

- Jack

...and that's where the difference between running a "safe" tune versus one on the verge of detonation comes in. Factory tuning runs a little less timing and a little more fuel at WOT because of the variances in temp, air density, blah, blah...but there is power to be found up there.

[Power Hungry]

Here's a couple thoughts...

1) Open Loop only affects fuel delivery calculations, not spark timing or shifting.

Open Loop and Closed Loop are two terms used to describe the fueling mode the computer is in.

In Closed Loop fueling, the computer takes readings from the oxygen sensors which read +/- of 14.64 AFR (Stoich) and makes corrections for it. If your car is idling @ 13.5 AFR, the 02s can see this, and will know to pull out enough fuel to get back to stoich.

In Open Loop, the fueling is purely based off the MAF transfer function and the open loop fuel table. This table has to be calibrated any time you make MAF changes, and changes that affect the airflow of the MAF.

When a car is started, the computer is in Open Loop until certain criteria is met. The O2 sensors need to be heated to work properly, so this is the main reason there is a delay.

After the sensors are heated up, the car goes into Closed Loop and the O2 sensors make their corrections.

The computer will go back into Open Loop under a variety of conditions. Throttle Position (TP) is one way.

There are parameters in the computer that determine what the TP is for Open Loop, and other things.

When that TP is reached, and the car goes Open Loop, and richens up.

2) Open Loop and WOT are 2 different things. Granted, a calibration will go into Open Loop at WOT but it it can also go into Open Loop based on other criteria.

3) WOT mode occurs at a predetermined point in the calibration and is based on a calculated voltage value from the APP (accelerator pedal position) sensor. This value can be changed to meet the performance need of the vehicle and/or driver.

4) During Open Loop at WOT, there are two things happening: First, the PCM goes into Open Loop fuel mode and runs based off the Open Loop fuel table and MAF. Second, the PCM goes into WOT Fuel Enrichment which provides an extra shot of fuel to help maximize torque output as well as reduce combustion temps. This is the WOT Fuel Multiplier found in the custom options. Since the target fuel ratios are richer at WOT than at cruise, you are often actually safer running at WOT than you are at cruise. Of course, fuel economy is going to be severely affected.

5) At WOT, shifting will revert to an RPM based strategy instead of the normal MPH vs. APP strategies. What the PCM tries to do is anticipate when to shift based on the target shift RPM and the current rate of acceleration of the engine. Based on calculated factors, the PCM determines how long the upcoming shift will take to complete and generate an RPM value at which to begin the shift procedure. This is MUCH trickier than it sounds and more involved than I'd care to get into at this moment.

6) Spark Timing is based on Load and Engine Speed, but is also heavily influenced by AFR, Engine Temp, Air Temp, Knock Sensor input, and other factors. This is not directly affected by WOT or even Open Loop, but can be indirectly affected by changes in AFR as a result of going into WOT or Open Loop modes.

There is a tremendous amount of data being processed inside the average vehicle's PCM. In fact, the 04-08 uses a derivative of the Power PC processors to handle meet these needs. Feedback (Closed Loop) systems try to maintain a zero control error, but that is only if the values from the sensors are accurate and why many CAI kits cause problems. Without changing the appropriate tables, the MAF data being returned to the PCM no longer has any direct relationship to the actual amount of air entering the engine. From that point, all other calculations based on MAF value are going to be incorrect - both Closed Loop and Open Loop.

I hope this makes sense. It did to me at 1:00 in the morning.

[Dfishrmn]

[B]3) WOT mode occurs at a predetermined point in the calibration and is based on a calculated voltage value from the APP (accelerator pedal position) sensor. This value can be changed to meet the performance need of the vehicle and/or driver.

Bill,

About where does this occur (APP) in your standard tunes and custom tunes. I am not an automotive engineer so have only a rudimentary understanding of all the values used and how it changes WOT. I guess what I'm asking is as a rule of thumb is it at 80%, 90%, 100% APP? etc.

[Jackpine]

One of the things I love about these forums, and this one in particular, is all the nifty knowledge you can pick up by reading them and asking questions.

Thanks, Bill - that was a super contribution!

- Jack

[Chris74]

Originally Posted by JackandJanet

One of the things I love about these forums, and this one in particular, is all the nifty knowledge you can pick up by reading them and asking questions.

Thanks, Bill - that was a super contribution!

- Jack

agreed...Bill's a walking book of knowledge when it comes to our trucks

I love his long winded posts

[Power Hungry]

Originally Posted by Dfishrmn

3) WOT mode occurs at a predetermined point in the calibration and is based on a calculated voltage value from the APP (accelerator pedal position) sensor. This value can be changed to meet the performance need of the vehicle and/or driver.

Bill,

About where does this occur (APP) in your standard tunes and custom tunes. I am not an automotive engineer so have only a rudimentary understanding of all the values used and how it changes WOT. I guess what I'm asking is as a rule of thumb is it at 80%, 90%, 100% APP? etc.

As a rule of thumb, it's between 90%-94%.