dangonay

Anyone here familiar with designing electronic circuits?

I managed to build my own digital meter to measure injector on time (with 1/10 ms resolution). That was the easy part. Now I'm trying to come up with a circuit which will show me the injector duty cycle (also digitally). This is proving to be beyond my abilities as I'm only a hobbyist.

Here are the details for you electronic technicians:

To measure the on-time of the injectors, I simply counted pulses (from a 10KHz clock) while the injector is on. I can also do the same for the off-time. But then I would have to divide these two numbers to get duty cycle. This seems a bit more complicated than I could do with a bunch of IC's. I want to stay away from microcontrollers (dont know how to use them).

Any ideas?

Mike O.

Buy a VAG-COM and then you can data log it (and do other cool stuff)

®ob

I think the one I have can do it, but I'm not sure. Never had to so I don't really know

dangonay

which can do this. I'm looking to build a gauge I can install in my car permanently.

Mike O.

...do this?

Does this parameter tell you how your car is performing? Does it correlate with another parameter? Is it something that you can control? Does it have to do with anything remotely performance oriented as a stand alone value?

Nope, Nope, Nope, Nope and Nope

I would really like to know what you are trying to accomplish with this single value. Injector duty cycle is not necessarily on time divided by on time + off time. This would make a WOT injector on time of 16.32ms at 1500rpm look a lot different than 16.32ms at 7000rpm even though they are both theoretically over 100% of duty cycle for a Bosch injector.

Bosch injectors are considered static (100% of duty cycle) at 14.50ms. Almost every tuner I've seen uses 16.32ms as their topline injector pulse width.

Really - what are you trying to learn from this parameter or what are you doing with it? Even if you are providing feedback to a chip tuner, they will ask you for every paramer BUT injector timing (that is their job to figure out).

Mike O.
Mike O.

DaveD4

If you want to steer clear of microcontrollers, then you may want to look into analog circuitry to do it. For example, an integrator could give you a output voltage proportional to the pulse width. Problem is, as rpm changes it will change the output too... You would have to generate another signal based on rpm to correct for it. This could get complicated.

OK, one more idea.. Capture both on and off times as you are doing now. Put a d/a on the output of each. Now you have a dc voltage proportional to each time. Use opamp to compare the two. DC output of opamp could drive an analog or digital meter.

I still have to say that a microcontroller would be a natural for this application.

hth,
Dave

dangonay

If possible, I want to fire the stock injectors with an external driver to extend their pulse width and add the extra fuel when nitrous is flowing (the Venom system operates like this, but they don't make a kit to fit Audi). I think this is infinitely better than fiddling with the fuel regulator to increase pressure. This will also allow me better control so I can progressively add nitrous and control fuel to match. As an example, the Venom system monitors the injectors and will only add so much nitrous. Once the injectors are maxed out, it ceases to add nitrous. I am essentially trying to build my own version of a Venom.

Before I can do this, I need to gather info on how the stock injectors fire. As well, when I start working with firing the injectors myself, I need to be able to monitor them (a scanner won't pick up my additional injector drive). This is why I want to make the gauge (plus, I like experimenting).

BTW, according to my math, an on-time of 16.32ms at 7000 RPM corresponds to appx 685 degrees of crankshaft rotation. Do you mean to tell me that Audi fires the injectors before and after the valves are open? A 270 degree cam would only open the valves for about 6.5ms at 7000 RPM. These are some of the things I want to find out.

Edited: Oh, I forgot. A circuit which can measure on time and duty cycle is the basic building block of my nitrous system, regardless of whether I decide to keep it as a gauge.

zain

Divide is a pain, so do it once and use a look-up-table. So you got a counter whose output is 8, 10 12 bit, whatever. You got another counter, same thing. One is on-time, the other is off. Or one is on time, the other is engine RPM, whatever.

Toss the 8 bits from one into the lower byte of an EPROM's address inputs, and the 8 from the other into the upper byte. (If you got more than 8 bit counters they you may need wider EPROMS on some in paralell, but it works out the same).

Then burn the EPROM so it's memory is loaded with upper-8 divided by lower-8. Then it will output the division results. If you're one step more clever, program the EPROM so the output is not the mathematical division result, but rather the correct values to light up a multi-segment display (or bar meter, or whatever you want)

Never do math, when you can store all possible results in a cheap LUT.

zain

Cheap D/A converters for each counter output. Then use an analog divide chip (yes they make them, or used to). Two voltages in, division result out. Check PMI/Analog Devices web sites for part search.

Only makes sense if you want duty cycle on an analog meter, if you're going to A/D it to make a digital display then go with my LUT suggestion.

Or get a micro controller... after a while with enough custom circuits you may wish you did.

Mike O.

...and I may be able to guide you a little bit here.

First of all, I can tell you that my programming does indeed fire the injector for 16.32ms per pulse at WOT all the way to 7500rpm. As stated, this pulse width is considered static by Bosch.

Good move on not messing with the Fuel Pressure. VW/Audi already uses an above average fuel pressure so adding any extra will prove difficult to tune because the added pressure will not correlate with added fuel.

The really bad thing about trying to do what you have described is that the injectors in the Audi are already maxed out if you are running a chip. Adding any extra timing will do nothing to add fuel. The only way around this would be to swap the injectors and go with a custom program that takes this into account. 310cc injectors are readily available and cheap but the programming may cost you more than it's worth.

My suggestion would be to add a second set of injectors or go with a fogger setup. The Audi fuel pump will work for this setup as long as you are running no more than a K04 as the stock fuel pump tends to have a hard time keeping up over 350hp.

Let us know how you make out.

Mike O.