Gallons Per Hour Error?

[landspeed]

My car has these kind of injectors too; a basic way to do this would be to assume the injector is 'on' when it falls below 10 volts, and 'off' when it goes above 10 volts *and doesn't go below 10 volts for 0.5 milliseconds*. Then you would have all your injector readings reading 0.5ms too high, but the software would subtract 0.5ms from all readings to correct for this.

(I'm assuming that 1ms = the large squares on the graph above).

This may be difficult if the ATMEL 'trigger' feature is being used to detect injector on / off phases; if this is the case, and enough spare CPU power is not present, a seperate device could be made, with a basic CPU, which does the above processing, and outputs a signal to the MPGuino. A setting in the configuration of the MPGuino would the correct for the fact that the injector readings are too long!

[Superturnier]

I made a circuit to filter the short pikes from the injector signal.



The idea is that it follows the falling edge immediately, but the rising edge is followed after a short delay.
Also I put some diodes to the ground wire of the mpguino that will raise the ground level of the mpguino about 2 volts higher than the car ground. A diode usually has a treshold voltage of about 0,5 - 0,7 volts in the conducting direction. This fools the mpguino to see a 4,5 Volt signal as a zero. Normally a signal between about 0-2,5V is considered as zero.
There's a 500kohm trimmer potentiometer to adjust the filter so that mpguino will see the pulse as a single pulse (this can be seen on the rpm value)

Here's the signal before and after filter:


And the same thing with more wide throttle:

[Cheese]

Originally Posted by Superturnier

I made a circuit to filter the short pikes from the injector signal.

...

Have you tried this in your car yet, and if you have, have you successfully calibrated the MPGuino? My MPGuino has just been sitting on my desk for months now because I have a peak and hold injector and haven't yet found the time to anything with it.

[Superturnier]

Yes. I have had it in my car over a month now and I think the filter is working ok. The RPM reading on my MPGuino is very steady. Therefore I think it counts the pulse as a one pulse.

Calibrating takes quite a long time. I started fooling with the injector delay setting. I 'd like the MPGuino to be accurate both on driving and idling. The calibration factor affects more to driving and the injector delay setting affects more at idle and low load. I think.

Right now I have about 4% error compared to fuelings, but overall I'm happy with the MPGuino. It shows reasonable values in different loads and different speeds.

For example a trip with towing a trailer at 80 km/h (50MPH) resulted 7,3 L/100km (32MPG)
And the same trip without the trailer at same speed resulted 5,8 L/100km (40.5 MPG)

Althought the filter is working ok in my case, I cannot quarantee that it works with someone elses peak and hold injectors. There can be different ways to control a peak and hold injector in different cars.

[Superturnier]

I Just added a resistor to the filter schematic. It's in series with the adjustable resistor. Just in case if someone uses this circuit and turns the adjustable resistor to zero ohm.
Anyhow DC current should not get through from injector to ground via the filter because of the condenser, but just for the safety's sake I think this resistor should be added.

[Cheese]

The symptoms you described in your earlier post perfectly describe what I experienced when I had the MPGuino in my car still. I guess since the circuit seems to be working for you I may as well try it myself. It could take me a while to do, but I'll report back here and let you know if it worked for me.

[Superturnier]

Found this link that dcb had posted in post #31 in this topic

It describes two types of Peak and hold injectors. The other's hold part is done with limiting the injector current and the other one's hold is done with PWM signal. PWM means that the current is switched rapidly on and off.

I have the PWM version P&H injectors and the filter works with them.

One possible way to see which type of P&H injectors are in your car is, if you have the mpguino connected to your car:

1. Set the injector delay to very small (like 2us)
2. Start the car
3. Check the MPGuino RPM value. If the reading multiplies when loading the engine with low rpm, then it probably counts the short pwm pikes as different pulses.

Good luck Cheese!

[usergone]

Well... Looks like I get to jump on the peak and hold bandwagon as well. I have had the guino hooked up to my car, even without the vss, and noticed that the GPH only changes with RPM. I thought that was odd, because even if I floored it, the GPH would not change (until the RPMs went up)

So I measured the TBI injector... Yeah... 2 ohms...

Originally Posted by dcb

it looks like they use a shunt resistor and an op-amp. Not sure how it gets dialed in. The opto works by the voltage drop across the inector (for negative switched systems).

I was just thinking that I could use a shunt (if we're trying to measure current). I have no problem cutting my injector lead, or both leads for that matter. I already have one cut and spliced to my kill switch.

For clarification, all of these schemetics are going on the assumption that I am looking at a waveform like this:

...and want to pay attention to the "C" section.

Maybe like this?


The "A" lead would (I think) give a voltage signal that is proportional to the current. I have a LM358N opamp on hand, but can't say I know just how to hook it up! (the technical stuff, I think I have the basic logic idea)

Then maybe use this circuit?


Or, if you want a top trim (cut it off above X voltage)... (BTW, I am pretty sure I have the transistor in there wrong. I want it to be when the A input is higher that X voltage (controlled by the pot on the right) the output goes low, and makes the transistor cut off the current from the left side)


Wow, long post

[usergone]

I suppose I should "clarify the idea" in the last post. What I am trying to accomplish in the above post is...

The current supplied to the injector is converted to a voltage, by means of a shunt. The voltage difference across the shunt will be called voltage A.

If voltage A is less than X, but greater than Y, a 0 to 12V signal is supplied to the guino.

X would be to cut off the top current from the "peak," and the Y is to set a threshold for what constitutes the "hold" part of the injection cycle.

[usergone]

The previous 2 posts were just theory, but today I borrowed an oscilloscope and looked at my injectors. When I looked at the voltage across the shunt (.27 Ohms), I saw this:

(something like this)


The A section seems to be the "peak" and the B section seems to be the "hold" and also the "pulse width" that I care about. I watched the waveform, and when I turned on the A/C, the "B" section extended a bit. There ya go.

Could anyone offer me their expertise in how to trim/condition that signal?