DIY_EFI Digest Saturday, July 31 1999 Volume 04 : Number 443 In this issue: Re: DIY_EFI Digest V4 #439 From Cranking to Idle. See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Sun, 01 Aug 1999 00:26:43 +1000 From: Phil Lamovie Subject: Re: DIY_EFI Digest V4 #439 Hi All, Bill a sigle flare is the type you find on most gas sytems in the home. The copper pipe is forced by a tool into a 90 degree cone. Appropriate fitting behind the flare seals it to the nipple. A double flare is really an extruded collar made by forcing a small section of the pipe back on itself. Sort of an instant metal 'O' ring. Found mostly with automotive brake tubing and on most high pressure (80-90) psi Bosch type K efi sytems. They use different fittings. Don't mix them up. Regards Phil Lamovie injec@xxx.au cogito ergo zoom ------------------------------ Date: Sat, 31 Jul 1999 11:58:13 -0700 From: "John Dammeyer" Subject: From Cranking to Idle. Hi All, I have a question to the folks out there who have 'rolled their own' injection. Given that injection at cranking needs to start sometime during the intake stroke it's easy enough to program a timer from TDC to trip at a certain point to open the injector. A second timer set to go off after that can turn off the injector. Let's say at a cranking RPM of 200 an intake stroke takes about 150ms and the injector pulse needs to be 5ms. Best to inject somewhere in the middle of the intake so set the ON timer to go off after 75ms and the OFF timer to trip at 80ms. So we begin the Suck Squish Pop Blow cycle and at the first TDC of a particular cylinder we hopefully squish a good mixture and Pop. At this point, things start to move rapidly. ie: Depending on the mixture, obviously the Pop cycle could be going a whole heck of a lot faster than the cranking RPM based on the mass that needs to be accelerated and the current moment of inertia of the pistons, crank, flywheel (etc.) assembly. If the engine accelerates up to 600 RPM in the pop stroke (50ms per intake stroke) it may happen that injector that should open at the 75ms point doesn't because BDC occurs at 50ms. So a Timer for Injector ON doesn't work; during cranking. If injection was started at TDC during cranking and the OFF timer is used to turn off the injector 5ms later then this problem doesn't occur. However, at some RPM and fuel mixture point the injector will need to be on longer than the intake stroke so now it cannot be turned on at TDC. It needs to be turned on sooner than the Intake Stroke TDC so the timer has to be loaded at a different point. And at even higher RPM the intake stroke may overlap and take as long as 540 degrees of crank rotation. (75% duty cycle so perfectly plausible). So my question is how have other injection designers handled this? How is the high rate of acceleration that occurs while cranking the engine handled. My test bed is an electric motor turning the encoder wheel and this accelerates much faster than the engine so I can simulate a complete loss of injection pulses. Thanks, John ------------------------------ End of DIY_EFI Digest V4 #443 ***************************** 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".