MPGuino for Audi

[secmil]

Wow, many thanks for those pics for fuel consumption signal! I'll be tearing my car apart again this week I guess...

Assuming I can actually use the signal, and all.

[rmccomiskie]

I did some logging on the way home last night. At 75 mph, the engine is turning 3400 rpm and burning 22 mpg (my guesstimate). Here's the injector pulse width at that speed:



This one happens to be 550 micro seconds width. I logged a number of these and the average is around 562 uS.

For my 2.8 liter 12 valve V6, I calculate 100,890,240 uS per gallon. Once I get this installed and running we'll see how accurate that is.

BTW: I'm using a sound card oscilloscope program on my laptop to capture the signals. I have an audio cable connected to the car with a couple of resistors to drop the signal voltage below 1V. It's plugged into my laptop microphone input. Works just fine at the frequencies we're dealing with.

[rmccomiskie]

Originally Posted by dcb

If it actually conditions the signal, then you might need to adjust your "Injector DelayuS" from its default of 500. Or just tap an injector lead

Question: Since the Audi fuel consumption signal appears to be one pulse for every injector, do I have to change any settings. In my case, it's as though I am connected to all 6 injectors not just one.

My assumption is that the normal MPGuino hookup is one injector and the pulse width of that injector is being scaled up to represent the rest of the injectors. Right?

[secmil]

I would just assume that our setting for microsec/gallon (as it's called in the workspace) would just be 1/6th as much since there are six injectors reporting instead of just one.

I wish I wasn't having so many hardware issues so I could play with it and see what's what...

[dcb]

Originally Posted by rmccomiskie

My assumption is that the normal MPGuino hookup is one injector and the pulse width of that injector is being scaled up to represent the rest of the injectors. Right?

Basically.

Honestly though, I have no idea if that signal you have found will be accurate. We account for mechanical delay when measuring the injector pulse. I don't know if what you are looking at has accounted for that or not. You will have to carefully measure that pulse alongside the injector pulse and do some figguring if you want to be reasonably certain of the accuracy. I don't know how conditioned that signal has been, you are breaking new ground.

[rmccomiskie]

Originally Posted by dcb

...I have no idea if that signal you have found will be accurate. We account for mechanical delay when measuring the injector pulse. I don't know if what you are looking at has accounted for that or not. You will have to carefully measure that pulse alongside the injector pulse and do some figguring if you want to be reasonably certain of the accuracy. I don't know how conditioned that signal has been, you are breaking new ground.

Good point.

I'll check the pulse width at idle. Since the 'Injector DelayuS' value is 500uS, I'd expect to see a pulse width of 500uS plus whatever injection time is needed to sustain idle. If the pulse width is less than 500uS (assuming that's the correct delay) then it's likely that the fuel consumption signal subtracts settling time from the injector pulse and directly represents the actual injection time.

If I can easily get at an injector wire I can compare that signal as a crosscheck.

[rmccomiskie]

I logged the fuel consumption signal pulse width at different speeds and compared them:



The typical pulse widths are:

Idle = 450 uS
50 mph = 620 uS
60 mph = 740 uS
75 mph = 870 uS

Given that the idle pulse width is relatively large compared to the rest, I suspect that the settling time is contained in the signal. In fact, I'd bet that the fuel consumption signal is just a composite of all 6 injector signals with no other conditioning.

Also, since the Idle PW is less than 500 uS, the delay time should be something less. Maybe 400 uS. I have no idea. I'll have to play around with the settings against actual fuel burn to get an empirical value...in my 'spare' time.

[rmccomiskie]

I found this interesting bit of information at http://www.injectorcleaning.co.uk/flow.htm

Bosch Part Number: 0280150552 (crossref to 1992-98 Audi 12V V6)
156 cc/min @ 3 bar (44.1 psi)
Resistance: 15.9 ohms

Audi typically specs their fuel rate at 43.5 psi so 3 bar is close. I'd expect the installed flow rate to be about 150 cc/min.

[rmccomiskie]

Bump.

[dcb]

Are you sure you want to go through all this to avoid tapping into an injector wire? There are a few unknowns. What is the pulse width of the injector at idle?