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Old 02-26-2009, 11:58 AM   #861 (permalink)
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Moving Audi content from this thread to the MPGuino for Audi thread

I've taken up enough space here on Audi related investigation. I'm moving this discussion over to the MPGuino for Audi thread to keep it all in one place.

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Old 02-27-2009, 04:32 PM   #862 (permalink)
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Quote:
Originally Posted by Nevyn View Post
I think you are missing a step of addition - see page
What step is that?

BTW: In that Virtual Dyno site, gasoline doesn't weight 7 lbs per gallon. It's about 6.0 lbs per gallon depending on the temperature.
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Old 03-05-2009, 10:28 PM   #863 (permalink)
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Still working on the high GPH problem

I've switched my fuel flow input back to the ECU signal. Everything is working just fine except the high GPH when coasting. I repeat, the ECU signal works just fine. I've dialed in the VSS and the uS/gallon. I just don't understand why coasting behaves the way it does.

I've tracked the high GPH reading from instantgph() back to the external interrupt routine processInjClosed(). In that routine, the value returned by elapsedMicroseconds() jumps from a low value to a high value when I'm coasting.

The elapsed time is ~500-700uS at 30mph steady and increases with higher speed and acceleration. Seems normal. When coasting, however, it decreases to about 250-300uS where it suddenly jumps up to more than 11000uS. As the car slows further and the engine rpm decreases, the value starts rising from 11000 to 15-18000uS. It seems to follow engine rpm inversely. The lower the RPM, the higher the elapsed time. It acts like it switches and starts measuring the wrong part of the pulse. The point at which it switches coincides with the ECU signal going flatline.

I'm stumped! When the signal goes flatline, I expected that the external interrupt routines would not fire. However, I checked and found that the routines are firing normally when coasting and the signal is flat. How can that be?

Question: What signal voltage level is needed to trigger the external interrupt pins? The normal ECU signal is negative going. Looking back at my scope images of the flatline, I see that there are some verrry small positive blips. Could it be that they are triggering the external interrupts opposite of what is expected?

Grasping at straws here.
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Old 03-06-2009, 03:22 AM   #864 (permalink)
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Quote:
Originally Posted by rmccomiskie View Post
Question: What signal voltage level is needed to trigger the external interrupt pins? The normal ECU signal is negative going. Looking back at my scope images of the flatline, I see that there are some verrry small positive blips. Could it be that they are triggering the external interrupts opposite of what is expected?
The pins will signal an "on" @~2.5 volts on a rising signal, and "off" @~2.2 volt falling signal.

So is it just instant that is off? Can it predict gallons needed for a tank refill pretty well?
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Old 03-06-2009, 09:41 AM   #865 (permalink)
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Quote:
Originally Posted by dcb View Post
...So is it just instant that is off? Can it predict gallons needed for a tank refill pretty well?
I think it affects more than just instant because the elapsed time is added to 'tmpTrip.injHius' that eventually is added to the current and tank totals. I was able to zero in on the uS/gal pretty well but only because I did that on a long highway trip with a fillup at beginning and end. Very little coasting occurred.

I've observed that the maximum elapsedMicroseconds value even under hard acceleration is about 1900uS. I'm experimenting with an upper limit beyond which I set the elapsedMicroseconds to zero. Since it jumps from about 250-300uS way up to 11000uS instantly, I will assume that anything higher than the limit represents the flatline signal. I'll make the upper limit a setting parameter so I can play around with it.
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Old 03-06-2009, 01:54 PM   #866 (permalink)
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Okay then. The experiment worked. By excluding very high elapsed times, I've eliminated the high GPH readings.

Here's my changes:

Code:
void processInjClosed(void){      
//  long t =  microSeconds();
//  long x = elapsedMicroseconds(injHiStart, t)- parms[injectorSettleTimeIdx];  
  unsigned long t = microSeconds();
  unsigned long s = parms[injectorSettleTimeIdx];  //set to 72
  unsigned long x = elapsedMicroseconds(injHiStart, t);
  
  if (x >= s && x < parms[pulsewidthLimit]) {  //elapsed time within range of settling time(72) and upper threshold(3000)
    x -= s;                                    //then normal pulse, subtract settling time
  }else{
    x = 0;                                     //otherwise pulse width assumed to be zero
  }
  
//  if(x >0)  //no longer needed, x is guaranteed to be zero or greater
  tmpTrip.injHius += x;       
  tmpTrip.injPulses++;      

  if (tmpInstInjStart != nil) {
//    if(x >0)  //no longer needed, x is guaranteed to be zero or greater
    tmpInstInjTot += x;     
    tmpInstInjCount++;
  } else {
    tmpInstInjStart = t;
  }
  
  tmpInstInjEnd = t;
}
I found info for my injector that indicates the settling time should be 615uS using Yoshi's formula. I scaled that down to 72uS for the ECU signal based on the ratio of the ECU to injector pulsewidth.

The maximum pulsewidth that I've seen during normal operation is 1904uS. That's a full throttle run to redline. I've set the upper limit of the pulsewidth to 3000. I don't expect any combination of normal operation will get close to that pulsewidth.

So, the acceptable range of pulsewidths is constrained to 72-2999. Any elapsed time greater than that is assumed to be a flatline ECU signal.

In my experiment, the GPH now seems to operate normally, i.e. it drops to zero when coasting.

Now that I've found a solution, I'll merge the changes back into a clean copy of v0.75 and test it in the car for a while. I still need to fine tune the uS/gal setting for the ECU signal.

Last edited by rmccomiskie; 03-06-2009 at 02:16 PM..
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Old 03-07-2009, 11:54 AM   #867 (permalink)
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Smile Calibration data for 1997 Dodge B3500

1997 Dodge B3500 R-V Engine: 5.9 Transmission: 4spd auto VSS: 121785 usec/gal: 0111821079 NOTE: this is an American Cruiser class B motor home. Calibration was accomplished with a GPS after driving 480 miles.
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Old 03-07-2009, 02:51 PM   #868 (permalink)
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Quote:
Originally Posted by W8AEF View Post
1997 Dodge B3500 R-V Engine: 5.9 Transmission: 4spd auto VSS: 121785 usec/gal: 0111821079 NOTE: this is an American Cruiser class B motor home. Calibration was accomplished with a GPS after driving 480 miles.
Kewl! Put it in the MPGuino Wiki.
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Old 03-07-2009, 05:00 PM   #869 (permalink)
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I poked around that site, followed links, and killed about 4 hours and never did figure out how to post there.

It will take someone either smarter than me or with more patience to put the information where it belongs.

Thanks
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Old 03-08-2009, 01:21 PM   #870 (permalink)
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I looked at what others have done. If you click on your user id at the top of the wiki page, it should take you to a page with your user id. Click the edit tab. Here's an example of what I did.

Quote:
'''1997 Audi A6 Quattro'''

[[Image:manfred400x300.jpg]]

MPGuino Information

<<TBD>> Work in Progress!
In the table of car settings, click the 1997 Audi A6 link to see what that looks like. Click edit for the cars table and take a look at the format of the links to user pages. I uploaded a picture to the wiki and inserted a link to it in my page.

Good luck.

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