Unwanted output signal jitter

[LinkMTech]

Hi skimask,
I'm putting this circuit between the motorcycle's ECU and fuel injectors. You may already know how they work but just for clarification; the ECU will pull the injector low for about 2.5ms and it's pulse width will vary about 8%. I want to to able to expand that to about +/- 20% within three RPM ranges along with some other fancy hoop jumping.
The -20% control will delay the ON time of the output signal to the injector but supposed to keep the OFF time unchanged for reduced pulse width.
The +20% control should keep the ON time intact but delays the OFF time of the output signal for increased pulse width.
I tried PULSIN, that will never do. Especially at 14K RPM where I will have to deal with input signal overlapping!
I tried PULSOUT, looked promising, if I was helping an old lady across the street, but that got nasty looking with all the looping and checking I had going.
So dealing with the signal as it happens seems to be the right direction if only for the jitter at the opposite end!

[skimask]

the ECU will pull the injector low for about 2.5ms and it's pulse width will vary about 8%

On all of the fuel injectors I've ever put a 'scope on, the pulse varies a heck of a lot more than 8%. I'd even venture to say that any injector's pulse width would vary 8% at a steady state just to keep the closed loop program in the ECM happy. It's possible this bike has something else going on that keeps the fuel injector pulse practically steady, but I tell ya, that's something I haven't heard of lately.

The -20% control will delay the ON time of the output signal to the injector but supposed to keep the OFF time unchanged for reduced pulse width.
The +20% control should keep the ON time intact but delays the OFF time of the output signal for increased pulse width.

If it was me, I don't think I'd delay the start of the pulse. If you delay the pulse width at the start, the fuel might not be there in time for the intake valve to open. Remember, it takes X amount of time for an injector to open and start spraying that nice cone shape properly, whereas the closing an injector is much more of a solid event, at least that's what I've seen from the high speed video from one of my relatives at GM (neat video too, can see practically every tiny little droplet of atomized fuel in the spray pattern). I think I would shorten up the tail end of the pulse. If anything, at least the fuel will be sitting there on the intake valve or at least in the intake stream, ready to be sucked in, even if it is pooled up on the intake valve, which in any halfway decently designed intake system, will get swirled up and re-atomized by the swirl and heat of the valve.

But, be all that as it may be, it's nearly impossible to determine what the ECM will determine should be the NEXT pulse width. If it was me, I think I'd try a system that would LAG by one pulse event. Keep tabs on the previous pulse, modify that pulse width, shoot that pulse width on the next event, while at the same time, using a timer, measuring the current pulse width, while again, using a timer, to keep track of the current pulse width and stop it as required.
But then again, as fast as today's ECMs operate, it may (and probably will) still flag a failure and go to open loop, because you're messing with the pulse width, thereby the air/fuel ratio, which the ECM will eventually see in the O2 sensor. Unless, you plan on running open loop continuously...which in that case...never mind...Go for it! Just remember that a stoich A/F ratio of 14.7:1 with 20% of the fuel removed is an A/F ratio of about 17.6:1...lean enough to make donuts out of piston heads and make sticks out of exhaust valves and instantly put ports in your otherwise smooth cylinder walls!

[LinkMTech]

But, be all that as it may be, it's nearly impossible to determine what the ECM will determine should be the NEXT pulse width. If it was me, I think I'd try a system that would LAG by one pulse event. Keep tabs on the previous pulse, modify that pulse width, shoot that pulse width on the next event, while at the same time, using a timer, measuring the current pulse width, while again, using a timer, to keep track of the current pulse width and stop it as required.

That was my initial thought too! But since I'm just coming out of the starting gate, I didn't know how that would be possible without a crystal ball. Thanks to some info I found on slick ways of using timers by DT, you're right, I think I will drop the notion of delaying the start of the pulse and keep tabs of the previous pulse to work off that.
This circuit will not be used blindly but in a monitored state on a dyno and is only the basis of the system. I know there are products out there for this but then there are also more than one type of shoes too.
Thanks for the confirmation!

[skimask]

This circuit will not be used blindly but in a monitored state on a dyno and is only the basis of the system.

I guess my big question is...why do you want to mess with the pulse width anyways?
Are you adding on some crazy turbo, tuned pipe type things or what?
I mean, closed loop is closed loop is closed loop. It's efficient, clean, keeps parts where they're supposed to be, etc.etc.etc. (and again I don't what kind of system you're dealing with).
Now...WOT is another story... Are you looking to basically 'bypass the rom' in the ECM and feed more fuel under WOT/open-loop conditions?

[LinkMTech]

I guess my big question is...why do you want to mess with the pulse width anyways?
Are you adding on some crazy turbo, tuned pipe type things or what?

Most street bikes (not all) do not currently use an O2 sensor, so minor adjustments to the fuel delivery are possible and needed in different parts of the RPM range when aftermarket upgrades are installed and will help smooth out the power delivery. You'd be surprised how much a little improvement feels "at the seat of the pants" to the rider. Maybe you already know.
Now the +/-20% range is adjustable and will probably never see 20% and may be reduced to some narrower range in the end, but until then, I'm starting at +/-20%.

Now since I'm taking your advice to sample the leading pulse to configure the next pulse out, I downloaded Mr. DT's Instant Interupt-14 super duper program template and aww man, all I could do was look straight up! You guys are in the zone to understand this stuff. But if I'm gonna eat that elephant, it'll be one byte at a time.
Quick question,... will I need to have a PIC device with 4 timers to be able to trigger off 4 inputs to "sample one, build the next"?

Thanks

[b1arrk5]

In keeping with my philosophy of keeping it simple, how about this idea, dump the ADC altogether, and use the CCP input to read the signal pulse duration. Bruce has posted an example how to do it using Darrel's Instant Interrupts. Instead of a pot to adjust, just read two buttons, up and down. I think you could get far greater resolution than you will turning a pot, and you could read the buttons using interrupts, or watch them in a loop. Wouldn't the four input signals, and the four injector pulses be pretty much identical for each revolution? I wonder if you could just read one or two input pulses on each revolution, and make all the outputs identical. Given the mass of the pistons and the fact that they are connected to the same crankshaft I'd be surprised if there needs to be a great variance between cylinders on a single revolution. If you can assume that the input signals and output signals would be identical that makes you job a lot easier, one timer would do it. I'm thinking that having an up and down button would allow a rider to make adjustments on the track, not just on a dyno, it would be hard to tweak a pot while sitting on a bike at speed, and eventually you will likely want to get this on the road I imagine. Your software could adjust the range of adjustment based upon the rpms of the engine, so at higher rpms you couldn't make a drastic change if you held a button too long, but at lower rpms holding the button could make a faster (greater percentage) change.

Jerry.

[b1arrk5]

I found the link I was thinking of;
http://www.picbasic.co.uk/forum/show...errupt+capture
this shows Bruce's example for reading the pulse width.

Jerry.