DIY_EFI Digest Tuesday, December 7 1999 Volume 04 : Number 680 In this issue: Insane MR2 project? Re: DIY_EFI Digest V4 #679 Re: Getting facts straight! (3/3) See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Tue, 7 Dec 1999 10:28:58 +1300 From: "Nicholas Parker" Subject: Insane MR2 project? Hello, what is the e-mail address of the the person modifying the supercharged MR2? I own a 1987 Supercharged MR2 with a few mods, and am also part way through making my own fuel and ignition ecu based on an 80552 chip and coded in assembler, but I'm moving to a 9x faster DSS87c550 mpu, and may re-write the code in C. My rpm,sampling, fuel, ign loop calculating loop already runs at about 200Hz @xxx.06MHz on the '552 but more power means 3d smoothing/interpolation calc for fuel and ignition maps. I'd like to hear from you. Nick Parker. ------------------------------ Date: Mon, 6 Dec 1999 14:37:08 -0800 From: "John Dammeyer" Subject: Re: DIY_EFI Digest V4 #679 Hi Phil, I haven't seen any specification information that states what the maximum ON time is for an injector before damage occurs and this is the data that actually determines the extreme end of the duty cycle in the terms of maxium on time. After all, if the duty cycle were restricted to one turn of an engine then at 600RPM I have, with 80% duty cycle, a possible pulse width of 80ms which is far higher than the 12.8ms that I am currently restricting my injector too. Now I realize that's a bit overstated but I understood that the 80% rate is to avoid two things: 1. Injector overheating. 2. Injector float due to signal removal and re-application at a rate faster than the voltage can decay in the coil due to coil inductance. The injector then positions itself at an indeterminate state because the energy never really leaves the coil before the next application of voltage. This is one of the places where Peak/Hold injectors are far superior to Saturated. Please _do_ post a copy of the injector data sheets that state the maximum on time of an injector before damage will occur. As an aside, to add my own urban legend, I've run the Honda injectors for more than an hour at 6600RPM (without fuel) in the open air using a 12.8ms pulse rate and 73% duty cycle. At the end of an hour the injectors are certainly hot to touch but not so hot as to burn and certainly not as hot as I would assume the area above the intake valve is on an engine at 6600RPM. I have't tried running them with fuel for an hour but I would imagine that they would run cooler. The stumble only occurs when the throttle is snapped open as fast as possible. Normally on aircraft this isn't a good idea but on a hovercraft I could see some yahoo doing this. When the stumble occurs the O2 sensor goes off the scale in the lean direction so I assume that I should probably make the maxium pulse width RPM dependant so if the throttle is snapped open at idle, like an accelerator pump, I should give the injector a 40ms pulse (80% duty cycle at 1200RPM) or so every engine revolution. BTW, I'm also running sequential injection (not bank fire), so in fact at low RPM I'm firing an injector every 180 crank degrees. You could balance a coin on the engine it idles so smoothly. Cheers, John >Date: Tue, 07 Dec 1999 03:12:56 +1100 >From: Phil Lamovie >Subject: Re: cycles > >Hi John et al, > > >...but an engine cycle is 720 degrees and therefore, at 7000RPM, with >an 80% duty cycle the max pw is 13.7ms. > >Yes John your quite right a 4 stroke IC engine has a working cycle >that >encompasses 720 degrees of crank. On the other hand an Injector is >not any IC engine and has a duty cycle that is of one revolution only. > >This does of course give rise to the question... are you only >injecting every second revolution of the engine ? If so that may >establish part of the reason for the stumble you are experiencing. > >Phil > > ------------------------------ Date: 07 Dec 99 22:26:17 +1200 From: "Tom Parker" Subject: Re: Getting facts straight! (3/3) Greg Hermann wrote: >So--what are we left with that is magical about stoich? The facts that a >stoich mixture is the point where a three way catalyst works best for >cleaning up tailpipe emissions and that it is also the point where a >standard EGO or HEGO exhaust oxygen sensor (as opposed to a UEGO WBO2 >sensor) switches its output. Period. So do the EGO sensors work at stoich because they were designed to work at this ratio, or is there something intrinsic about their operation and the conditions at stoich that causes this? I guess the OEM's wouldn't be using them if they didn't work at stoich, so it doesn't really matter if it is easy to make them this way or not. A better question would be are they cheaper than the wide band sensors because they are easy to make, or because they are used on so many cars? - -- Tom Parker - parkert@xxx.nz - http://www.geocities.com/MotorCity/Track/8381/ ------------------------------ End of DIY_EFI Digest V4 #680 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. A non-digest (direct mail) version of this list is also available; to subscribe to that instead, replace "diy_efi-digest" in the command above with "diy_efi".