DBW pedal position correlation with throttle body

[Jim_PA]

Oh yeah, I tried the corvette APP on the corvette pedal with the wires going where they were supposed to go, and it didn't work.

So, I put the truck APP back on the corvette pedal, cut the end of the pedal off, mounted it to the floor, and I have the BMW gas pedal actuating the Corvette pedal...

I have yet to have a problem over-extending the pedal like I did with the truck pedal when I gave it full travel. Maybe the corvette pedal does have less overall travel.

Still, the TB is open 100% at maybe closer to 3/4 of pedal travel. Maybe this is normal.

Can't wait until a part needs to be replaced, I'll have no idea what to order somehing for

[turbo_bu]

Thanks for the follow up. Guess that throws my theory of the APP could be from any vehicle as long as the wires were hooked up correctly out the window ...

[swingtan]

Have you tried logging both APP and ETCTP in scantool? You may find that the pedal sensor is reporting "WOT" at half travel, hence the TB being set to wide open by the ECM.

Simon.

[Jim_PA]

That seems to be the case, but figuring out what is not matched properly has stumped many people.

[swingtan]

The ETC system is fairly simple in operation.

The APP sensor provides a 0-5V signal to indicate the throttle position. Generally it's "around" 0V at closed throttle and "around" 5V at WOT. the WOT voltage could be anything from 4V to 5V depending on the application. The ECM will take this voltage and convert it to an actual pedal position, then command an associated throttle blade opening. the TPS then is used to measure the actual throttle opening and is again a 0-5V signal, as for the APP sensor, low voltage is closed and high voltage is open. If you read the wrong PID's in Scantool, you will get an actual TPS reading that only goes from 20% to about 85%, because the older GM.TP PID actually reports the TPS sensor voltage percentage rather than the actual opening %.

So here's what I'd do...

• Measure the actual Applied Pedal Position sensor voltage to see what output voltage is sent from the pedal. To do this,
  
  • Measure the 0% pedal height from the floor. Let's use 5 inches as an example.
  • Depending on how accurate you want to get, divide the height into the number of test points you want. 5 should be enough for a test, so we will test for pedal changes of 1 inch.
  • Check the APP sensor voltage at 0% pedal and note it down.
  • press the pedal down 1 inch and again note the voltage of the sensor.
  • Take further readings at 1 inch increments.
• Use the above data to see what the sensor is telling the ECM the actual pedal position is.
• If you have logged both APP and ETCTPS, look at the correlation between the two and you should be able to work out where the "pedal" position needs to be to achieve 100% on the throttle blade.
• You now have two choices...
  
  1. Alter the physical travel of the pedal so that 100% throttle blade open occurs at 100% pedal movement.
  2. Alter the sensor OP voltage so that the sensor voltage for 100% throttle blade opening occurs at the current 100% pedal movement point.

If the vehicle is being used for circuit work, then the 0% throttle position is critical to allow for effective "heel - toe" work during cornering. This should be kept in mind if altering the actual pedal travel.

Simon.

[Jim_PA]

Well, as a follow-up.. I've been driving the car for about a month now, and I'm worried about my clutch life. If I can concentrate heavily on extremely lightly feathering my gas pedal, all goes well. But if I'm trying to get up and go in a hurry, My gas pedal foot tends to bump the throttle a bit more heavily.. Not good for the clutch!!!

So, as a hopeful work-around, I observed TP% while doing what I consider "bumping" the throttle while pulling out, and TP% goes up to usually about 50% in what I consider normal pedal actuation. Seems a bit aggressive to me

So, I started messing with B2308 "ETC pedal response"

Stock values from 12.50% to 50% pedal go like this, along with my 50% reduction:

pedal % - Throttle % (stock) - Throttle % (with my modifications)
12.5 - .381 - .190
15.63 - .586 - .293
18.75 - .947 - .474
21.88 - 1.377 - .688
25.00 - 1.895 - .947
28.13 - 2.539 - 1.270
31.25 - 3.389 - 1.694
34.38 - 5.703 - 2.852
37.50 - 7.5 - 3.750
40.63 - 9.6 - 4.8
43.75 - 12.002 - 6.001
46.88 - 14.502 - 7.251
50.00 - 16.904 - 8.452

After multiplying the values up to 50% by 1/2, I added a sharp curve from 50% up to 100%.

I realize that by doing this, I've lost some pedal granularity above 50% throttle movement, but in reality, it's pretty rare I'm looking for pedal control/granularity above half throttle anyway.

In the driveway, the pedal feels MUCH more reasonable now, and I might have taken away too much, but I'll have to reserve that judgement until I do some driving.

I have my fingers crossed that the modifications don't trigger a limp mode or fry my PCM (as warned about in the editor...) but I'll have my laptop and a backup file on hand in the event that it does.

[Jim_PA]

Oh my! What a difference in overall light throttle driveability. Any pre-mature clutch wear from this point on is all in driver error. Feels like a totally different car now.

Wish I would have done this sooner.

[swingtan]

Sounds like you have got it nailed. Good work.

[joecar]

Jim, thanks for the follow up

[Jim_PA]

I generally prefer to solve the problem rather than circumvent it, but with this one, I just need to keep telling myself it's OK that I can't figure it out