DIY_EFI Digest Thursday, 21 November 1996 Volume 01 : Number 354 In this issue: RE: Air Flow Measurement RE: Air Flow Measurement RE: Air Flow Measurement RE: Air Flow Measurement Re: Electromotive TEC-II? Re: Diff between theory and practice Re: Air Flow Measurement Re: Air Flow Measurement RE: Air Flow Measurement Re: Air Flow Measurement Injection timing Re: Electromotive TEC-II? Re: Air Flow Measurement House Cleaning, stuff for sale Re: Air Flow Measurement Re: Electromotive TEC-II? Re: Air Flow Measurement RE: Air Flow Measurement Re: Air flow & such Re: Air Flow Measurement RE: Air Flow Measurement RE: Air Flow Measurement Re: Injection timing Re: Air Flow Measurement Re: Electromotive TEC-II? Re: Air Flow Measurement Re: Air Flow Measurement Re: Diff between theory and practice re: Air Flow Measurement Re: Air Flow Measurement See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- From: Stephen Dubovsky Date: Wed, 20 Nov 1996 13:03:17 -0500 Subject: RE: Air Flow Measurement ... >>I think if most people who swear by MAF had a reference airflow >>measurement to compare it to, they'd be horrified! > ... Ok, so go buy a $90 vane/rotating type meter that is 1-2% accurate and get a curve for your MAF to linearize it. Heck, take the throttle body off the car (w/ the intake plumbing intact), put the vane sensor on a pipe at the output (to make the flow even and laminar) and stick the whole thing out the window of you car and take some data points;) Should be really easy to find a 2nd,3rd,...nth order approx to linearize the sensor (or use yet another LUT (look up table) for the computationally challenged). ------------------------------ From: "George Najarian" Date: Wed, 20 Nov 96 10:01:13 -0800 Subject: RE: Air Flow Measurement On Wed, 20 Nov 1996 01:06:52 -0600, Robert McElroy wrote: >The main reason I don't want to use an existing MAF sensor is that I don't have one >to play with. Also, I am under the impression that most heated-wire MAF's output >a frequency signal. Since I am a mechanical engineer and don't have much knowledge >when it comes to A/D conversion techniques, I would prefer to use a sensor that will >output a voltage signal (something I am slightly familiar with.) The Ford (Hitachi) MAF output a voltage and can be bought new for ~150-~200 or so. Used ones go for considerably less. George Najarian | '95 Ford Mustang GTS E/SP (14.21/100.81) najay@xxx.0/93) http://users.deltanet.com/~najay/ Team.Net Team OS/2 ------------------------------ From: cloud@xxx.edu (tom cloud) Date: Wed, 20 Nov 1996 12:21:57 -0600 Subject: RE: Air Flow Measurement [ snip ] >Perhaps it's this difficult precisely because it is a huge >capitalistic venture. The formula for Coke is probably >not a huge technical surprise, but keeping it a secret >maintains its value. > >>You know -- if someone would market an "open architecture" (a la S-100 >>bus, IBM-PC) efi, I believe he could make a whale of a lot of money. > >Most drivers just want to get in the car and drive. The number >of people who care more about how the engine works than about >how many doors the mini-van has is very (sadly) small I'd wager. > >>Something that majored in simplicity and gave the customer source code >>(probably in BASIC) so he could build on what he got. > >There are all sorts of non-technical issues with that. For >instance, who would be legal liable. I was talking about for tinkerers -- not a product by major mfgrs; something by, say Wesley and Knighton or such, for the rest of us dummies. Tom Cloud ------------------------------ From: cloud@xxx.edu (tom cloud) Date: Wed, 20 Nov 1996 13:25:07 -0600 Subject: RE: Air Flow Measurement >> *Every* mail message you send out has a uuencoded section >>titled "WINMAIL.DAT." >> >> Please, see if you can configure your mail sender not to >>include that. > >I will stop sending mail (after this) until I'm sure that >only the ASCII text will be sent. (Trouble is when I receive >a copy of my own mails from the diy_efi mailer, I never see >any uuencoded trailer.) > >Please accept my apology for prior inconveniences. Don't go away, Anthony -- I really want to hear your input. Tom Cloud ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 15:41:10 -0500 Subject: Re: Electromotive TEC-II? David Gould wrote: > > Perhaps this is not truly diy, but... > > I autocross a 1.8 liter Mazda Miata. I am allowed by the rules I run under > to replace the entire intake and exhaust systems, but not to modify the > engine internals. Some of the other competative cars (Miatas, RX7s, CRXs) are > using the Electromotive TEC-II system to control fuel and ignition. I have > looked at the Electromotive manuals and it looks like a reasonable system to > me, but I am not an expert and have little to compare it too. > > Since this car is both a race car and a daily driver in CA, I will have to > face the smog check every two years. It looks like the simplist solution > would be to replace the original system, get the smog cert, and put the > Electomotive back on every two years. Bummer. > > Given all of the above, is the Electromotive a reasonable system? I am vaguely > aware that there are others (Motec etc) out there, but am under the impression > that they cost quite a bit more. Is there another system I should look at? > > Is there anything especially good or bad about the Electromotive? > > I noticed in the manual that it does not have some of the frills that the > stock system has like idle control adjusted for electrical loads, EGR control, > purge canister control. Do I need all this stuff? I suspect not, except for > the purge control. How do I do the canister purge without the stock ecu? > > Will there be drivability problems with the Electromotive? What about weather > and altitude changes? Again, the stock ECU looks more sophisticated, but then > cars ran on carburators (a french word meaning 'don't mess with it') which > were even less sophisticated than the Electromotive. > > Any experience with Electromotive as far as reliablity of the system? Do they > support the product and handle repairs etc well? > > Any special gotchas or neat hints for this application? > > Thanks for any and all advice. > > -dg > > David Gould dg@xxx.6383 > Informix Software (formerly Illustra) 1111 Broadway #2000 Oakland, CA 94607 > - A child of five could understand this! Fetch me a child of five. Another one you may want to check is Haltech. I had a bad experience with Electromotive when I was in college. We had problems reading RPM at cranking speed. Needless to say it caused a lot of dead batteries and damaged starters! But that was six years ago. Since then I have talked to several people who have used the system with no problems. Regarding idle control and canister purge, a good option is to leave the factory electronics intact, and let the factory system control these functions, while you use a simple aftermarket system like electromotive to control the fuel. The only problem is that the "check engine" light will come on. If this was a domestic car, I could sell you all the "fixes" you need to prevent the light from comming on. But since it's an import, you may have to put up with it, and clear codes and reconnect the factory system before your inspection! Best Regards ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 15:53:07 -0500 Subject: Re: Diff between theory and practice jon hanson wrote: > > hopefully someone can explain the following deviation from theory to me > The engine is a 1985 USA spec Toyota 4age 16 valve twin cam. > the factory engine management system has been removed and replaced with > a programmable system (controls fuel and ignition timing). The Toyota TVIS > flaps have been removed from the intake manifold (the new ecu cannot control > them). The O2 sensor is removed and the system is always open loop. > the system uses a MAP sensor and a TPS. > Peak torque occurs at 4800 rpm acc to spec. I recently had the car on a dyno > and was adjusting the fuel myself. At 4800 rpm I had a WOT fuel no of 155 to > achieve a CO reading of 3.5%, at 6000 rpm I had a fuel no of 170 to get a > CO of 3.5%. Accoarding to my limited knowledge peak volumetric efficiency > coincides with peak torque. I would have expected to have the highest fuel no > at around 4800 rpm and then seen them drop slightly as revs got higher > but the opposite happened. I'm a great believer in doing something and > seeing the results for yourself. Can anyone explain why this is so, I'm > curious to know. > > Jon Hanson > Johannesburg > South Africa. Volumetric efficiency represents a percentage of maximum flow rate with no dynamic considerations. In other words if you take actual corrected air flow (in this case it is your fuel flow * A/F ratio), and divide it by: displacement * RPM / 2, the answer is your volumetric efficiency. Notice the RPM term in this equation. As the RPM goes up, your engine simply breaths faster, eventhough it doesn't breath as efficiently. That is why you need the extra fuel. If you could optimize your cam and intake runners to deliver maximum torque at 6000 instead of 4800, you will find your fuel requirements increase, because you just improved your volumetric efficiency. Best Regards Mazda Ebrahimi ------------------------------ From: "David Mcintyre" Date: Wed, 20 Nov 1996 16:06:15 -0500 Subject: Re: Air Flow Measurement Hey Anthony, I'd rather read the crap at the end of your messages that have your withdraw from the conversation...I'm really learning stuff here. I hope my message didn't convey the wrong tone! -Dave ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 16:09:10 -0500 Subject: Re: Air Flow Measurement > Still seems to me (I'm still fishing for a definitive answer) that > TPS, BAP, MAP and TEMP (IAT) would give a very reasonable approximation > (after correction for non-linear TPS vs. opening area) of MAF. No ??? > > Tom Cloud Yes. But don't forget the idle air bypass motor. Also, what the automotive manufacturers do with their sensors is not necessarily just for air mass flow calculations. Even if they decided to do away with MAP in air mass flow calculations, they would still need it or another way of determining EGR rate for diagnostics. Here is another important point: Under part throttle conditions, air mass flow is greatly affected by throttle angle and pressure drop accross the throttle blade. This affect is the dominant factor in determining air mass flow. By contrast, the closer we get to WOT, the more actual air mass flow is affected by the dynamics of the engine (intake runner length, plenum volume, cams, etc), and the less it is affected by pressure drop across the throttle. So it would make sense to use a weighing system to base mass flow calculation based on throttle angle at lower manifold pressures, and base it on MAP the closer we get to WOT. Right? I know this is getting too detailed. The bottom line is that you CAN use TPS instead of MAP. and yes, you do need intake air temp regardless. Chow for now Mazda Ebrahimi ------------------------------ From: cloud@xxx.edu (tom cloud) Date: Wed, 20 Nov 1996 16:08:09 -0600 Subject: RE: Air Flow Measurement This stuff stuck on the end of some messages is a MIME encoded message. Decode it with "munpack" or any other MIME reading software. Mpack/munpack is available via anonymous FTP at ftp://ftp.andrew.cmu.edu/pub/mpack/ for the PC world it's mpack15d.zip. Now, for youse guys more sophisticated than I, the mail prog I use is Eudora. It has a switch to send attachments in either binhex or mime. I have it set for mime. Why won't it decode the mime stuff I receive? (I guess the answer is obvious -- it's not an attachment.) Tom Cloud ------------------------------ From: cloud@xxx.edu (tom cloud) Date: Wed, 20 Nov 1996 16:45:51 -0600 Subject: Re: Air Flow Measurement >> Still seems to me (I'm still fishing for a definitive answer) that >> TPS, BAP, MAP and TEMP (IAT) would give a very reasonable approximation >> (after correction for non-linear TPS vs. opening area) of MAF. No ??? >> >> Tom Cloud > >Yes. But don't forget the idle air bypass motor. I don't think I have one o' those. Actually, I know I don't, since I'm using a throttle body from Holley. But, if I decided to modify my oem '91 F-150 EFI I guess I'd have that problem. Also, what the automotive >manufacturers do with their sensors is not necessarily just for air mass flow >calculations. Even if they decided to do away with MAP in air mass flow calculations, >they would still need it or another way of determining EGR rate for diagnostics. I don't got that (EGR) either. >Here is another important point: Under part throttle conditions, air mass flow is >greatly affected by throttle angle and pressure drop accross the throttle blade. This >affect is the dominant factor in determining air mass flow. yep, I can understand that By contrast, the closer we >get to WOT, the more actual air mass flow is affected by the dynamics of the engine >(intake runner length, plenum volume, cams, etc), and the less it is affected by >pressure drop across the throttle. So it would make sense to use a weighing system to >base mass flow calculation based on throttle angle at lower manifold pressures, and base >it on MAP the closer we get to WOT. Right? > >I know this is getting too detailed. The bottom line is that you CAN use TPS instead of >MAP. and yes, you do need intake air temp regardless. > >Chow for now >Mazda Ebrahimi I guess I understand. I wanted a system that would compensate for altitude and barometric / atmospheric changes .... hence BAP. I can see that MAP might could be ignored and just BAP and TPS (plus IAT) used to give a very workable efi system .... is that what you're saying? Just seems to me that BAP - MAP = delta P across a known opening (the throttle). Why is that any different at WOT? And it looks like that would work quite well at idle and low throttle, where the MAF sensor is at its weakest performance point. Course, I'm thinking about standard manifold, too. I can see that runners and TPI could greatly affect the equation, as there might not be a _real_ definitive MAP reading (would be different at different places ???). So, you're saying that speed density is _very_ adequate? I think I knew that?? I wanna know what's wrong with my assumptions -- why do oem's go to all that trouble and expense to put in MAF if it can be calculated from sensors already in place? (I understand that there might be bypasses that degrade the data -- but seems that could be overcome.) Tom Cloud ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 17:52:44 -0500 Subject: Injection timing Hi everyone, As I understand it, it is best to inject the fuel after the intake valve closes, so the fuel vaporizes on the somewhat hot cylinder head surfaces. Is this true? Is there any advantage to injecting at other times during the cycle? If so, explain the reasoning. Thanks, Mazda Ebrahimi ------------------------------ From: dg@xxx.com (David Gould) Date: Wed, 20 Nov 1996 14:56:08 -0800 (PST) Subject: Re: Electromotive TEC-II? > Regarding idle control and canister purge, a good option is to leave the factory > electronics intact, and let the factory system control these functions, while you use a > simple aftermarket system like electromotive to control the fuel. The only problem is > that the "check engine" light will come on. If this was a domestic car, I could sell > you all the "fixes" you need to prevent the light from comming on. But since it's an > import, you may have to put up with it, and clear codes and reconnect the factory system > before your inspection! Do you mean basically to wire it up like this: Stock ECU Inputs: water temp, tps, crank pos, egr valve pos NORMAL MAF, air temp DISCONNECT Outputs: radiator fan, ISC valve, egr, canister purge NORMAL ignition, injectors, fuel pump relay DISCONNECT Electromotive: Inputs: water temp, IAT, MAP, crank pos, tps Outputs: ignition, injectors, fuel pump relay So that basically the stock ecu runs the cooling fan, EGR, cannister, and idle speed while the new ecu runs the timeing and fuel. Clever idea, anyone ever do this? - -dg ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 16:19:32 -0500 Subject: Re: Air Flow Measurement George Najarian wrote: > > On Wed, 20 Nov 1996 01:06:52 -0600, Robert McElroy wrote: > > >The main reason I don't want to use an existing MAF sensor is that I don't have one > >to play with. Also, I am under the impression that most heated-wire MAF's output > >a frequency signal. Since I am a mechanical engineer and don't have much knowledge > >when it comes to A/D conversion techniques, I would prefer to use a sensor that will > >output a voltage signal (something I am slightly familiar with.) > > The Ford (Hitachi) MAF output a voltage and can be bought new for > ~150-~200 or so. Used ones go for considerably less. > > George Najarian | '95 Ford Mustang GTS E/SP (14.21/100.81) > najay@xxx.0/93) > http://users.deltanet.com/~najay/ > Team.Net Team OS/2 I think I have a couple of those (used) at work laying around somewhere. They are from a 4.6L ford. Anyone interested. Give me an offer. Mazda Ebrahimi kleenair@xxx.com ------------------------------ From: Sandy Date: Wed, 20 Nov 1996 15:20:01 -0800 Subject: House Cleaning, stuff for sale House cleaning time again, I have a couple of SBC's in the closet, and they are for sale. BCC-52 Binary Technology 8052 (8051 with rom basic, can be disable), proto area on board, and on board rom burner. Includes the manuals, intel basic ref, assembler, power supply for board, and VPP for rom burning. Board size about 5x9 80535 from Tri-L data, small size 4x5, includes daughter card with dallas ram, and clock, power supply, manuals, etc. Has all the usual junk, rs232, 422, etc. I also have a bunch of DigiBoard 8x, 8 port intelligent rs232 boards if anyone needs them. For more details drop me a mail, all prices are very reasonable... Sandy ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 18:46:51 -0500 Subject: Re: Air Flow Measurement tom cloud wrote: > I wanted a system that would compensate for altitude > and barometric / atmospheric changes .... hence BAP. I can see that MAP > might could be ignored and just BAP and TPS (plus IAT) used to give a > very workable efi system .... is that what you're saying? NO. You need MAP. > Just seems to > me that BAP - MAP = delta P across a known opening (the throttle). Why > is that any different at WOT? My only concern is that at near FULL LOAD, your delta P is very small (may be a few inches water column maximum. Under this condition the throttle no longer controls (or limits) air flow, therefore it is not adequate to just measure delta P and correct for temperature. Also, remember full load does not necessarily mean WOT. Consider that at 1500 RPM, at thirty to forty percent throttle openning, you may already reach your maximum air flow (i.e. manifold pressure is almost atmospheric). By contrast, at part throttle, since the main restriction IS the throttle blade, you can simply use a look-up table to calculate air flow based on TPS, MAP, and BAP, and then correct for temp. Notice no RPM term is involved here. When delta P across the throttle is small, what limits the flow is essentially the flow through the intake valves which also relates to intake manifold dynamics (which are RPM related). Under these conditions, an RPM based table is needed. I guess you could make it TPS vs RPM instead of MAP vs. RPM, but using TPS for this purpose is not accurate. Remember that at lower RPMs you loose a lot of accuracy with the TPS, because the last 2/3 of your throttle openning do nothing to the flow. > And it looks like that would work quite > well at idle and low throttle, where the MAF sensor is at its weakest > performance point. Course, I'm thinking about standard manifold, too. > I can see that runners and TPI could greatly affect the equation, as > there might not be a _real_ definitive MAP reading (would be different > at different places ???). You are very correct about the definitive MAP reading part. I have access to the logic of a natural gas fuel injection system, and they use an averaging scheme to dampen the MAP sensor input! I wouldn't be surprised if other do the same to stabilize the MAP signal. > > So, you're saying that speed density is _very_ adequate? I think I knew > that?? I wanna know what's wrong with my assumptions -- why do oem's go > to all that trouble and expense to put in MAF if it can be calculated > from sensors already in place? (I understand that there might be bypasses > that degrade the data -- but seems that could be overcome.) > This is just my opinion, but a very good reason for using MAF from an OEMs point of view is that the engine calibration process becomes much much simpler. You simply get one signal that tells you the air mass flow. I can't think of an easier way of doing it. > Tom Cloud ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 18:53:59 -0500 Subject: Re: Electromotive TEC-II? David Gould wrote: > > > Regarding idle control and canister purge, a good option is to leave the factory > > electronics intact, and let the factory system control these functions, while you use a > > simple aftermarket system like electromotive to control the fuel. The only problem is > > that the "check engine" light will come on. If this was a domestic car, I could sell > > you all the "fixes" you need to prevent the light from comming on. But since it's an > > import, you may have to put up with it, and clear codes and reconnect the factory system > > before your inspection! > > Do you mean basically to wire it up like this: > > Stock ECU > > Inputs: water temp, tps, crank pos, egr valve pos NORMAL > MAF, air temp DISCONNECT > > Outputs: radiator fan, ISC valve, egr, canister purge NORMAL > ignition, injectors, fuel pump relay DISCONNECT > > Electromotive: > > Inputs: water temp, IAT, MAP, crank pos, tps > Outputs: ignition, injectors, fuel pump relay > > So that basically the stock ecu runs the cooling fan, EGR, cannister, and idle > speed while the new ecu runs the timeing and fuel. > > Clever idea, anyone ever do this? > > -dgWe have over 700 vehicles running on a secondary fuel injection system using this method. The only problem you are going to have is the check engine light, and there are ways around that if you are clever about it. Here are some common tricks: - -Send a fake O2 signal to the factory ECU to make it happy, - -Simulate OEM injector resistances with a resistor bank, so its happy, - -Send a fake temp on the coolant sensor to freeze adaptive learn if that is a problem - -Or if everyting else fails, send a clear code signal to the ECU every once in while. I have access to such a box for Ford and GM OBD-II computers. If you are making major intake and exhaust modifications you probably wouldn't want to do this, but you could also relay your injectors, so you can flick a switch and go back to the factory fuel curve on the fly! ------------------------------ From: cloud@xxx.edu (tom cloud) Date: Wed, 20 Nov 1996 19:06:46 -0600 Subject: Re: Air Flow Measurement [ snip'a'lot ] >You are very correct about the definitive MAP reading part. I have access to the logic >of a natural gas fuel injection system, and they use an averaging scheme to dampen the >MAP sensor input! I wouldn't be surprised if other do the same to stabilize the MAP >signal. So, would one route a small line from each runner to a central 'orange juice can' (a la Ford) or some other 'integrating' device? Clearly, the time constant would be a consideration (too big a canister, too slow response). Maybe just the time constant of the lines going to a central collector might be enough averaging to give reasonable MAP. Anyway, thanks for discussing this with me. Tom Cloud ------------------------------ From: dave.williams@xxx.us (Dave Williams) Date: Wed, 20 Nov 1996 18:15:00 +0000 Subject: RE: Air Flow Measurement - -> Ok, so go buy a $90 vane/rotating type meter that is 1-2% accurate - -> and get a curve for your MAF to linearize it. I'd love to. Where can I purchase such a meter? ------------------------------ From: "George M. Dailey" Date: Wed, 20 Nov 1996 19:45:50 -0600 (CST) Subject: Re: Air flow & such First off, I think you would have to know how the flapper system calculates or estimates mass air flow. Probably a function of flapper position and inlet air temp. The next step might be to establish a flapper position voltage and inlet air temp voltage for a given MAF voltage. This could be easily done with a data logger and a flapper and MAF sensor mounted in series while driving the car. Once you've estabilished this relationship over the operating range of the engine, you simply build a "black box" to convert the MAFs frequency or voltage output to the equivelent flapper position and inlet air temp (voltage,curent, or resistance) that the ECM expects to see. There are a few blow flies in the oil though. If you don't know how the flapper system calculates or estimates mass air flow, there could be problems. Coolant temp might be factored in for example. A simpler solution might be to use a MAF system off of an exiesting OEM MAF equiped engine of the same # of cylinders and approximat displacement. Good luck, GMD At 10:20 AM 11/20/96 UTC-2, you wrote: > I have wanted to get rid of the restrictive >> flapper type in favor of the hot wire or film type .. >...Hi! I also want to get rid of that flapper: ... the problem I guess is to get the signals matched, and the >problem with THAT is that the flapper has a weird change in >resistance as you sweep across. ... >As far as I know, the flapper initially overshoots a bit, which acts >as a sort of acceleration enrichment. But its wide open from about 3- >3500 rpm, anyway. > >Anybody? > >Sincere;y >Andrew > > > > > > > > >Dr A. N. Bosch >Physiology Department/ Sports Science Institute >University of Cape Town Medical School >P. O. Box 115 >Newlands 7700 >South Africa > > ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 20:45:27 -0500 Subject: Re: Air Flow Measurement tom cloud wrote: > > [ snip'a'lot ] > > >You are very correct about the definitive MAP reading part. I have access > to the logic > >of a natural gas fuel injection system, and they use an averaging scheme to > dampen the > >MAP sensor input! I wouldn't be surprised if other do the same to > stabilize the MAP > >signal. > > So, would one route a small line from each runner to a central 'orange juice > can' (a la Ford) or some other 'integrating' device? Clearly, the time > constant would be a consideration (too big a canister, too slow response). > Maybe just the time constant of the lines going to a central collector might > be enough averaging to give reasonable MAP. > > Anyway, thanks for discussing this with me. > > Tom Cloud The best way is to find a spot in the main plenum volume that is not near any runners. However, with some manifolds, like Ford's split plenum 5.0L or 5.8L, the signal is still unstable. As you said, a vacuum canister would dampen the signal fluctuation, but it also slows the signal down. But I don't think that is very critical. Generally speaking, you should use the MAP primarily under steady state conditions, and TPS under transients, therefore the responsiveness of the MAP sensor is not super critical. Any how, without having access to detailed code, it is hard to determine how your system responds to an erratic MAP signal. Maybe they already have an averaging scheme built into the software! An alternative to the canister approach is to use an orfice tube before the sensor (this is the approach we use), but essentially they both do the same thing. This was a very interesting discussion. Best Regards, M.Ebrahimi ------------------------------ From: "George M. Dailey" Date: Wed, 20 Nov 1996 19:58:04 -0600 (CST) Subject: RE: Air Flow Measurement Good lord, are you inferring that my hot PLATINUM wire Bosh MAF sensor, valued at $500.00, is more than -+ .005% off!! Say it isn't so. GMD At 08:45 AM 11/20/96 -0500, you wrote: > >>I think if most people who swear by MAF had a reference airflow >>measurement to compare it to, they'd be horrified! > >I think you might be right. ------------------------------ From: "George M. Dailey" Date: Wed, 20 Nov 1996 20:20:45 -0600 (CST) Subject: RE: Air Flow Measurement At 01:25 PM 11/20/96 -0600, you wrote: >>> *Every* mail message you send out has a uuencoded section >>>titled "WINMAIL.DAT." >>Please accept my apology for prior inconveniences. > >Don't go away, Anthony -- I really want to hear your input. > > >Tom Cloud I second that Anthony, sure I have to hit the down key a few more times than necassary, but I think you're worth it. GMD ------------------------------ From: "Jeffrey Engel" Date: Wed, 20 Nov 1996 21:15:07 +600 Subject: Re: Injection timing Mazda Ebrahimi As I understand it, it is best to inject the fuel after the intake valve > closes, so the fuel vaporizes on the somewhat hot cylinder head > surfaces. Is this true? Is there any advantage to injecting at other > times during the cycle? If so, explain the reasoning. Yes, please do. Grumpy Jenkins said in his book that 85% of the fuel vaporization occurs in the cylinder. 'Couse he's talking race engines versus whatever we're running (street / HiPo / semi-race / whatever). It would be nice to know what the current state-of the art is. I've also heard that EFI-equipped engines are sensitive to air-speed. With the injectors down near the ports, I'd have thought air speed wouldn't be that important. je jengel@xxx.net ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 21:36:52 -0500 Subject: Re: Air Flow Measurement George M. Dailey wrote: > > Good lord, are you inferring that my hot PLATINUM wire Bosh MAF sensor, > valued at $500.00, is more than -+ .005% off!! Say it isn't so. > > GMD > > At 08:45 AM 11/20/96 -0500, you wrote: > > > >>I think if most people who swear by MAF had a reference airflow > >>measurement to compare it to, they'd be horrified! > > > >I think you might be right. Although I have never verified the accuracy of MAF sensors myself, SAE papers I have read indicate MAF is very accurate. Also, speed- density basically predicts the efficiency of the engine at pumping air, given manifold pressure and RPM. This characteristic can change over the life of an engine (or even from engine to engine) in mass produced cars. Neither of these will cause an error with MAF. Maybe that is a reason why OEMs use it? ------------------------------ From: "William A. Sarkozy" Date: Wed, 20 Nov 1996 22:20:31 -0800 Subject: Re: Electromotive TEC-II? At 11:00 PM 11/19/96 -0800, you wrote: > >Perhaps this is not truly diy, but... > >I autocross a 1.8 liter Mazda Miata. I am allowed by the rules I run under >to replace the entire intake and exhaust systems, but not to modify the.......... I run a ACCEL/DFI and have had very good luck. My friends run Haltech and have had very good luck. I've heard some people talk down the ElectroMotive system, but I have no direct experience with it. With these modern systems, there's no reason to switch induction systems to meet emissions standards. Both the Haltech and the DFI can run in closed loop mode for the emissions test, and then you can load a new program for the track (probably open loop). I can't speak for the Haltech, but the DFI has all kinds of bells & whistles for AC compressor loading, knock sensor input, relay contact closure for nitrous, etc. Good luck, Bill ------------------------------ From: Mazda Ebrahimi Date: Wed, 20 Nov 1996 20:47:32 -0500 Subject: Re: Air Flow Measurement Dave Williams wrote: > > -> Ok, so go buy a $90 vane/rotating type meter that is 1-2% accurate > -> and get a curve for your MAF to linearize it. > > I'd love to. Where can I purchase such a meter? > Does this rotating type meter restrict air flow? Is it designed for automotive applications (i.e. can it be accurate under vibration and shock)? ------------------------------ From: Tuck Date: Wed, 20 Nov 1996 21:59:20 -0500 Subject: Re: Air Flow Measurement Speaking of a vacuum canister, any ideas on where I could source something like that? I recently ported the motor on my RX-7 and I think that the map sensor is getting a little confused so I'd like to play with a vacuum accumulator or something of the sort. Justin "Tuck" Cordesman SOLID BRASS-> A Solid Silver Mean Machine. I think I see her. I think I want her. I think I love her. She's just killing me. SUCK MY BLOOD! ------------------------------ From: "John Faubion" Date: Wed, 20 Nov 1996 21:00:50 -0600 Subject: Re: Diff between theory and practice > Peak torque occurs at 4800 rpm acc to spec. I recently had the car on a dyno > and was adjusting the fuel myself. At 4800 rpm I had a WOT fuel no of 155 to > achieve a CO reading of 3.5%, at 6000 rpm I had a fuel no of 170 to get a > CO of 3.5%. Accoarding to my limited knowledge peak volumetric efficiency > coincides with peak torque. I would have expected to have the highest fuel no > at around 4800 rpm and then seen them drop slightly as revs got higher No what your seeing is correct. The engine is most efficient at peak torque so the amount of fuel needed is at its lowest point. At the higher RPM levels the efficiency drops off and the engine requires more fuel. ------------------------------ From: oecar1@xxx.au Date: Thu, 21 Nov 1996 10:59:05 +0800 (WST) Subject: re: Air Flow Measurement >Ok, so go buy a $90 vane/rotating type meter that is 1-2% accurate >and get a curve for your MAF to linearize it. I'm afraid to disappoint you, but there just 'aint such a beast. The error specs for most automotive spec thermal MAFs are +/-4% of value. A flapper type AFM would never even come close to this. I have used both a NIST traceable Subsonic Venturi and a NIST traceable Laminar Flow Element for my reference airflow measurement (+/-0.5%). Each of these is worth upwards of $US2500 a piece. >Heck, take the throttle body off the car (w/ the intake plumbing >intact), put the vane sensor on a pipe at the output (to make the >flow even and laminar) and stick the whole thing out the window of >you car and take some data points;) I've been using an engine dynamometer. MUCH more convenient, but the problem is not in collecting the data... >Should be really easy to find a 2nd,3rd,...nth order approx to >linearize the sensor (or use yet another LUT (look up table) for the >computationally challenged). I have a fourth order curve which fits my data to better than 1% RMS error when testing at steady state flow. The problem is that steady flow conditions only exist at very low throttle openings. As you open the throttle the steady flow starts to become pulsating flow and if you're unlucky it will turn into reverse flow at some point. To give you an idea of the magnitude of this, at WOT, 2250 rpm on the engine I'm working on (4-cyl) flows about 37g/s average, but between 25 and 54 g/s peak-to-peak. The frequency is twice engine speed for obvious reasons The problems become apparent when you know that the sensor output is non-linear, the frequency response is asymmetrical, and any reverse flow signal will be rectified. This means that the true average (voltage) signal will not represent the true average airflow. Any digital approximation to this will only be worse unless you use a few tricks. To convert this analogue signal to a useful byte or two, you must perform some A-D conversion. So you are quantising it not only in the range, but also in the (time) domain. If you don't do this syn- chronously (ie you sample in the time domain) you will wind up with a very noisy (and aliased) signal. If you do it synchronously (in the crank domain) you have to decide what angle gives you the represent- ation of the average airflow. Your sample angle cannot be calculated (easily) and varies significantly with engine speed (and to a lesser extent with throttle position) I guess what I'm trying to suggest is that (from my experience at least) the MAF is no slap-it-on-and-go solution. A MAP sensor on the other hand is linear, can be throttled to give a physical average or can be sampled and averaged/filtered in the time domain without difficulty. It has it's disadvantages, but... There's heaps more to be said about this subject but I hope it's useful to share this with you guys. If anyone has any other ideas or experience on getting MAF's to work well, I'd love to hear from them. Andrew Rabbitt Orbital Engine Company Perth, Western Australia ------------------------------ From: "John Faubion" Date: Wed, 20 Nov 1996 21:15:02 -0600 Subject: Re: Air Flow Measurement Anthony (or anyone else using Microsoft Internet Mail) Set your options for your out going mail as follows: Under Mail (on the menu bar) go to Options. On the Send tab under Mail sending format, click the button for Plain Text. Then click the Settings button to the right of that. Now click the button for Mime. Then make sure the box beside Encode text using: is set to None. Now click on OK and then on Apply. This will make your messages compatible with the rest of the world. John Faubion jfaubion@xxx.net - ---------- > From: David Mcintyre > To: diy_efi@xxx.edu > Subject: Re: Air Flow Measurement > Date: Wednesday, November 20, 1996 09:46 > > Anthony, > *Every* mail message you send out has a uuencoded section > titled "WINMAIL.DAT." > > Please, see if you can configure your mail sender not to > include that. > > Thanks, Dave > > On Nov 20, 8:39am, Anthony Tsakiris wrote: > > Subject: RE: Air Flow Measurement > > > > >> Can someone guide me to descramble this? > > > > >i tried xferpro,(a mail-format de-scrambler, a must when transferring > > >thru some services) all formats with no luck. sorry. > > > > I've resent the message you're trying to unscramble. > > > > It looked to me like the scrambled version was uuencoded. > > (If you're on a Unix machine, check the man pages for > > uuencode and uudecode.) That format was entirely > > unintentional on my part. I'm trying for straight ASCII. > > > > Anthony Tsakiris > > > > begin 600 WINMAIL.DAT > > M>)\^(C,-`0:0" `$```````!``$``0>0!@`(````Y 0```````#H``$(@ <` > > M& ```$E032Y-:6-R;W-O9G0@xxx.;W1E`#$(`0V ! `"`````@`"``$$ > > MD 8`9 $```$````,`````P``, ,````+``\.``````(!_P\!````8P`````` > > M``"!*Q^DOJ,0&9UN`-T!#U0"`````&1I>5]E9FE 8V]U;&]M8BYE;F > M;RUS=&%T92YE9'4`4TU44 !D:7E?969I0&-O=6QO;6(N96YG+F]H:6\M > M=&4N961U```>``(P`0````4```!33510`````!X``S !````(P```&1I>5]E > > M9FE 8V]U;&]M8BYE;F > M```>``$P`0```"4````G9&EY7V5F:4!C;W5L;VUB+F5N9RYO:&EO+7-T871E > > M+F5D=2<``````@$+, $````H````4TU44#I$25E?149)0$-/54Q/34(N14Y' > > M+D](24\M4U1!5$4N1415``,``#D`````"P! .@$````"`?8/`0````0````` > > M```#W$T!!( !`!D```!213H@06ER($9L;W<@365A > M``X```#,!PL`% `(`"<`,0`#`%4!`2" `P`.````S <+`!0`" `D`"<``P!( > > M`0$)@ $`(0```#0P-$1"-T,U1#@T,D0P,3$Y1#9",# R,$%&1#,P-# T``(' > > M`0.0!@#4`P``% ````L`(P```````P`F```````+`"D```````,`+@`````` > > M`P`V``````! `#D`P(0/3>C6NP$>`' ``0```!D```!213H@06ER($9L;W<@ > > M365A > MK],$! ``'@`># $````%````4TU44 `````>`!\,`0```!P```!A='-A:VER > > M:4!P;V)O>"YS > M90```$-!3E-/345/3D5'54E$14U%5$]$15-#4D%-0DQ%5$A)4S])5%))1418 > > M1D524%)/+"A!34%)3"U&3U)-051$12U30U)!34),15(L04U54U172$5.5%)! > > M3E-&15)224Y'5$A255,``````@xxx.@(``,P#``!,6D9US"M+ > > M>/\`"@$/`A4"I /D!>L"@P!0$P-4`@!C: K > MR[0*#,Q,,%(\T`\8'$P* _GT*@xxx.!N > > M9S$P,Q60"PH7DO,,`1.@xxx." ^&]\ > M<&4"(&50(&=U:0VP( > (%AT;R -L 3Q80;0;/4A<6@$`#\*A1U/'E\ > M(8 (@60@>&8$D#$9R)"P@)R%U > M=VC_"? F(0!Q)J$%$!L@(YT0*2C0 > > M;)\#(">4!" #\")P(&XAH#$*0&-K+B!Q*A!Y+A\*CPN1$O$M`C(%22=V?R#@ > > M&7 1\ (P(F$A0@xxx.1D` > > M;VLF82&1(6%L:;\XH#33(>8F<#1 $>!I`B#5*4!A!"!U"E!N!: -L.)D,?8H > > M268UECK!)R"Z50,`>" > M*-!N)G [, 6"Y0VP+B_@xxx.O(TH6D9<&QY*]8VL+\+@"N00J$" > > M( = /.)M0P#M,C%T,8 T$6TV!B>1(' 1*:%I9V@%0$%30]1)23==00(P: (@ > > M0P!Z5#50:T+ ! `R!1B1``%)L ```P`0$ (````#`!$0`````$ `!S#0T^K; > > MY]:[`4 `"##0T^K;Y]:[`1X`/0`!````!0```%)%.B ``````P`--/TW```! > > !"M:[ > > ` > > end > > > >-- End of excerpt from Anthony Tsakiris > > > ------------------------------ End of DIY_EFI Digest V1 #354 ***************************** 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".