DIY_EFI Digest Wednesday, December 8 1999 Volume 04 : Number 683 In this issue: Injector Duty Cycle. GREAT! Re: Injector Duty Cycle. Fuel Injector Question [ADMIN] Lost messages 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 12:11:34 -0800 From: "John Dammeyer" Subject: Injector Duty Cycle. > >Date: Tue, 7 Dec 1999 07:52:41 -0700 >From: bearbvd@xxx.net (Greg Hermann) >Subject: Re: DIY_EFI Digest V4 #680 > >>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 [snip] >I would say that 80 or 85% is a good maximum duty cycle--at ANY engine >speed, for the cooling reason, and also just to leave a bit of head room at >the top end. > >2 ms minimum on time and 2 ms minimum off time, again at any engine speed, >is a decent rule of thumb to avoid fuel delivery inconsistencies. I think that's an unreasonable assumption. I've found that at idle using the stock Honda injectors (24lb/hr) that idle on a warm engine uses about 2ms pulse width for Stoich. I found when I tried to use 4ms as my minimum time that the engine barely ran. It may be that the injector at that pulse width is not opening completely but adding a too large value into the total injector time screws up all the other calculations. >> > >>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. [snip] >Are you saying that you have written your program to restrict the injectors >to 12.8 ms on time, regardless of engine speed?? yes. > If this is the case, and >you are getting the correct mixture at 6000 rpm, it is virtually a sure >thing that you are going to be lean at the torque peak (4500rpm??) . The >torque peak will always require a longer on time than the HP peak (more >fuel is needed PER revolution at the torque peak than anywhere else). (I >know, not quite true if the maximum bmep and maximum friction loss torque >do not occur at exactly the same engine speed. In the Honda's case the peak torque is up at 5000RPM which makes it so nice, with a 2.4:1 reduction drive, for aircraft. The Hovercraft Fan is pitched to provide maximum thrust at 2100RPM so this works out nicely. And yes, the mixture at 5000RPM is not 12.8ms. It's less. In fact watching the EGT it's fascinating to adjust the pulsewidth at that RPM by a tiny amount and watch the EGT go up as the mixture is leaned out and the EGT go down as the mixture is richened. Aiming for a particular EGT and O2 value has demonstrated that adjusting the fuel on either side of optimum causes an increase in either EGT or fuel usage without an increase in engine speed. This is a WOT. > >If you are programming in a maximum injector on time of 12.8 ms, I would >bet that this is the source of the lean transition. The nature of the load >curve for the hovercraft (fan, I presume?) is HP increasing with the cube >of the rpm--so--the lean problem MAY only be rearing its head on a >transition, only because you do not have enough steady state load available >at the torque peak to create the full fuel/air demand that the engine is >capable of at that engine speed. At 4000RPM and a partially open throttle, a sudden open to WOT creates a nice smooth (and quite fast) acceleration to 5600 with the Hovercraft fan so I'm not having acceleration enrichment problems with partially opened throttle. Just from idle to 2000RPM with a barely open throttle to WOT. The 12.8ms is to prevent a 'dramatic' cancellation of injection if a timer interrupt is missed because the injector is told to turn on (via compare with a register) after the compare point has already passed. It's the way I wrote the software. Perhaps I could have done it differently but I had one compare register to share among 4 injectors. This works fine if Injector 1 has to turn on before Injector 3 but if the mixture requirement changes so that on the intake stroke for Injector 3 a lot more fuel is required then it's possible that Injector 3 may actually have to turn on before Injector 1 because Injector 1 value was calculated for a different mixture requirement. The timer is already programmed to turn on Injector 1. The solution has been to immediately turn on Injector 1 if the turn on point for Injector 3 is earlier than for Injector 1. But this type of transition doesn't appear to occur under 3000RPM since I've set my maximum pulse width to 12.8ms. What I will try is to use the RPM as an index into maximum pulse widths so that I can set a larger pulse width for acceleration at lower RPM. Perhaps I should phrase a question in this way. For folks working with 1.6L engines that are fuel injected, what size injector do you use and how long an injection pulse width do you use if the engine is idling at 1000RPM and the Throttle is suddenly moved to WOT? ie: What Acceleration Enrichment do you use? Regrds, John ------------------------------ Date: Tue, 07 Dec 1999 13:27:45 -0500 From: Barry Tisdale Subject: GREAT! Nice job crapping up the list........ ------------------------------ Date: Tue, 7 Dec 1999 16:54:01 -0500 From: "Bruce Plecan" Subject: Re: Injector Duty Cycle. You're surprised by this?. 100% load at idle, and no where near peak torque, the "lambness, might not have anything to do withthe EFI, other then trying to tune around a poor design. is there any slippage in the system?. Just like boats can be really hard to tune, with prop drives (not sure about ducted fan stuff). Try a none sprung clutch disc, and sudden release pressure plate (with like 1:1 final drive gears, 2.5:1 first gear, and 40" tall tires).. Just trying to use other terms to express a point Grumpy | At 4000RPM and a partially open throttle, a sudden open to WOT creates a nice | smooth (and quite fast) acceleration to 5600 with the Hovercraft fan so I'm not | having acceleration enrichment problems with partially opened throttle. Just | from idle to 2000RPM with a barely open throttle to WOT. ------------------------------ Date: Tue, 07 Dec 1999 18:02:11 From: "Lawrence E. & Cathy R. Mayfield" Subject: Fuel Injector Question There is an ad on e-bay that has 8 "cleaned and tested" injectors. The only tech info is a number by the connector. It is 5235302. Does anyone recognize this? Sorta looks like a Lucas number.. Expires in 4 days, so help needed soon..e-mail me off list unless the info is germain to list. Many thanks in advance. L.E. Mayfield 124 Maximillion Drive Madison, Al. 35758-8171 1-256-837-1051 old >>>>>>>> http://www.hsv.tis.net/~mayfield new >>>>>>>> http://home.hiwaay.net/~lemayf DrMayf@xxx.com lemay@xxx.net <<< Subject: [ADMIN] Lost messages Due to a certain member that insisted on replying to every single message with his desire to be removed, at least one digest didn't make it out, so if you have posted something today and haven't seen it, could you resend it please. BTW, that certain member was reported to his abuse address... Not because he replied to all the digests, but because he included the entire digest in each reply and took me over my disk space limit. If you do want to unsubscribe, you should send unsubscribe diy_efi-digest in the _body_ of a message to majordomo@xxx. Note the '-digest'. Unfortunately, 'diy_efi' on its own doesn't work. 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