Post by thread:Ignition timing control

John Pearson wrote: > > I am thinking of ways to control the ignition timing advance curve of a > car. I was thinking that I might time the amount of time between cylinder > firings and divide that number by 360. Then I would know when to fire the > next cylinder after checking with a lookup table for the programmed curve. > > Is there a better or easier way? > > Thanks > > John One thing is to remember that the less calculations you have to do while the engine is running, the better. Two ways I have found around this, is to precalculate data that is used while the engine is running, or use a lookup table. I used precalculated data with 4 stages of advance, vac adv, dwell and RPM timing etc. It took a PIC 16F84 about 40 - 60 inline instructions to get the timing for all these parameters as well as do the actual timing from the results. Check out http://www.picnpoke.com/projects/ignition.html There is some early downloadable code there that uses a lookup table. -- Best regards Tony http://www.picnpoke.com spam_OUTsalesTakeThisOuTpicnpoke.com

John Wrote > I am thinking of ways to control the ignition timing advance curve of a > car. I was thinking that I might time the amount of time between cylinder > firings and divide that number by 360. Then I would know when to fire the > next cylinder after checking with a lookup table for the programmed curve. > > Is there a better or easier way? > Young Anthony Nixon of the PICLIST made and published through a magazine called Silicon Chip such a device using a 16C84 and a keypad. I would definitely talk to him. _____________________________ Lance Allen Technical Officer Uni of Auckland Psych Dept New Zealand http://www.psych.auckland.ac.nz _____________________________

Silicon Chip had a programmable ignition using a PIC ..... You may want to look at the article. The kits are still available, or the code may be of interest to you! http://www.picnpoke.com/projects/ignition.html Hope this helps ____________________________________________________________________________ ________________________________________________________ Gareth Bennett .....garethbKILLspam@spam@es.co.nz Systems Engineering (LMR Group) Otago/Southland Region New Zealand {Original Message removed}

John Pearson <PICLISTKILLspamMITVMA.MIT.EDU> wrote: > I am thinking of ways to control the ignition timing advance curve of > a car. I was thinking that I might time the amount of time between > cylinder firings and divide that number by 360. Then I would know when > to fire the next cylinder after checking with a lookup table for the > programmed curve. > > Is there a better or easier way? John: Why divide by 360 at all? I don't see what purpose that would serve... Anyway, it's harder than it appears; if you only have a low- resolution source of engine-position information (like the distributor), you'll probably find that your PIC will retard the timing whenever the engine's accelerated. You can get better engine- position resolution if your car has a crank sensor on the flywheel or something... But if you use that instead of the signal from the distributor, you'll no longer get free information from the distributor's vacuum sensor, which is sorta important if this is for a street-driven car, since you won't get real good drivability if you just use a hardwired curve. On the other hand, using the distributor signal (after it's been affected by the vacuum sensor) means that you might have to modify your curve to compensate for a non-optimal vacuum-advance. And... Since your engine presumably revs over a large range, you have to make sure that you're measuring time with high-enough resolution for accurate operation at redline, but not so finely that you overflow your counters at idle. There are LOTS of other software issues (and a fair number of hardware issues, as well), but those are the main ones. Ignition controllers are kinda complicated; the ones I did for Jacobs Electronics ran to over 10,000 lines of code. My personal inclination, if I were just doing this for my own car, would be to forget about putting a PIC in there and just take the distributor to a race shop and get it re-curved to my specs (or, if the car didn't HAVE a distributor, take the existing EPROM out of the ECU and have IT modified). If you DO decide to do this project, though, I can offer a bit of advice: Do all your testing on the bench, with a function generator replacing the car's distributor. Spark timing that's bad enough to cause detonation will kill an engine fast, and timing that's GROSSLY wrong will kill an engine REAL fast. Good luck... -Andy === Andrew Warren - .....fastfwdKILLspam.....ix.netcom.com === Fast Forward Engineering - San Diego, California === http://www.geocities.com/SiliconValley/2499

Andrew Warren wrote: > If you DO decide to do this project, though, I can offer a bit of > advice: Do all your testing on the bench, with a function generator > replacing the car's distributor. Spark timing that's bad enough to > cause detonation will kill an engine fast, and timing that's GROSSLY > wrong will kill an engine REAL fast. Good advice. Many a night, 'the shed' lit up due to carby and exhaust 'explosions'. Couldn't believe the PIC survived all the crap it had to put up with. Still got it somewhere. Keep naked working spark plugs away from the PIC too. It will start executing it's code upside down and backwards at the same time. Same goes for old copper cored spark leads. Very frustrating to find bugs if you are unaware of this. Avoid ground loops through the PIC PCB. If the coil (or other) suddenly decides to return it's current back through the PCB's ground due to a faulty connection, the PCB will light up "Eat at Joe's" for a split second then spit the dummy. I've seen it happen twice now. Make your circuit robust enough for a brown out situation, such as cranking with a half flat battery, and things such as load dumps etc. Sometimes the PIC can fire up or run in an erratic manner. One good thing about using a distributor with a 'home made' ignition system is that you can bypass the PIC circuit and connect the coil back up to the points to get home if something fails. The 8 bit timers in the PIC are not really set up for high revving accuracy. I think Motorola (are you allowed to say that here), have purpose built processors for ignition control, whether or not you can get them is another matter. I did some rough math awhile ago, and on older slow revving motors, using the distributor for a timing reference doesn't matter too much. Hi performance, Hi RPM is a totally different ball game though. Best left to the experts. I think one of the trickiest things is getting control of the engine just when you are starting to crank it. And then there's...and...and...and.. As Andy said, "a project like this is harder than it first appears". -- Best regards Tony http://www.picnpoke.com EraseMEsalesspam_OUTTakeThisOuTpicnpoke.com

John, That's basically the way the car mfg does it,(At least Ford I know). But the firing of the ignition is dependent on many factors..ie Engine Speed, Engine Load, Whether Accelerating or Decellerating, Temperature of Engine, etc., etc. So, it's not just a matter of adding a fixed value time period. It's a rather complicated process. It's doable, but it will take a little more calculation and thinking to come up with a lookup table that will help and not hinder. I've had some experience in this area, but I don't claim to be an expert by any stretch of the term. And my experience is limited at that. I'd be glad to help out where I can, but I will tell you now that I don't have the knowledge or expertise to do it all by myself if I were asked to. Anyway, let me know what you decide. Regards, Jim On Mon, 01 May 2000, John Pearson wrote: {Quote hidden}> > I am thinking of ways to control the ignition timing advance curve of a > car. I was thinking that I might time the amount of time between cylinder > firings and divide that number by 360. Then I would know when to fire the > next cylinder after checking with a lookup table for the programmed curve. > > Is there a better or easier way? > > Thanks > > John @spam@jimKILLspamjpes.com