Ok FROM WHAT I'VE FOUND mass air is a direct measurement of the amount of air going into the engine. The maf vr rpm is just a calibration of the maf.. as you would calibrate a mass flow meter or any other process instrumentation..... Map, is using a differential pressure to come up with an amount of air.. ie it is similar to measuring flow by measuring the pressure drop across an orifice plate.. the engine is the orifice plate in the pipe.. get it?? Now with an orifice plate, you need some constant or value that is particular to it to convert the pressure drop to flow rate.. for an orifice plate it is the coefficient of discharge.. The ve tables represent the coefficient of dischare of the engine ...in simplistic term(so don't flame me... I'm not about to go into the theory!!!) >From the pressure drop indicated from the map sensor the ve tables relate that pressure drop to a flow rate...except for an engine the cd is always changing.... So for a maf application.. the tables theoretically should not change for any motor you put the maf sensor on.. as long as that engine is within the span of the maf.. once the signal from the maf is calibrated to a flowrate... it should not change on any motor.... For map since the ve represents the cd of the motor... different motors will have differing cd's As disscused before on this list.. the maf runs into trouble with high perf engines because the engine pull more air than the ul of the maf.... Or the range of the maf is to narrow....if their was a maf that would measure a higher amount of flow it would be ideal.. cept you would then have to edit the tables to reflect the output of the maf to actual flow rate... another option that was discussed was to somehow patch the code so the maf range was 16bit instead of 8.. hence doubling the range..... I'm working on that right now by adding a table like the ve on the 730...maf high and maf low....where 255=255g/s and max on maf high would be 255 or 510g/sec.. so that one the maf sig reached 250 or so it would switch to maf high.. (there would also have to be compensaion for hysterisis ie goto maf high at 250g/s then go to maf low at 30g/s.. there is also some other avenues I'm looking at... Now that we have the air covered, we have to let the ecm know how much fuel to mix with that air.... Lets say the maf is calibrated.. then it has to know the fuel flow it gets this from the injector size. From the afr goal ie 14.7:1 it now knows how long to keep the injector open in order to get that ratio... some people fiddle with the injector size to fool the ecm.. I tend to like to calibrate the maf.....so the maf tables are right....then put the actual g/s of fuel my injectors put out (at their pressure) and change the a/f ratio till it is where I want it.... Then iu tune the spark back to afr... ect.. the maf tables can also be changed if you fingd a lean spot in your range .. but if calibrated right this should no happen... also the pe functions should be looked at in order to get max performance out of the motor..cause diff motors have differing likings for the amount of fuel you need when you mash the gas.... There is also tons of other stuff but this is getting prety long.. Mike Rolica Plant A, Magnesium Products Division Strathroy (519)-245-4040 Ext. 265 -----Original Message----- From: Rick Lindstedt [SMTP:rick@mafb.org] Sent: Thursday, June 15, 2000 12:44 PM To: gmecm@diy-efi.org Subject: Re: Changing 165 fuel delivery was "General tuning question -fuel economy" Marteney, Steven J. wrote: >I haven't got my copy of tunercat yet, but it's coming, or the rather the >check is going. In the meantime, to increase fuel across the board, TC has >two settings for injector flow rate, single and double fire. Is that what I >can use for this? I remember a couple of months ago there was a lot of I dont know about that one.. >hand-waving about single-fire and double-fire and what the difference was. >Hate to bring it up, but was there a clear answer that came out of that? No definete answer came ...I was the one that brung it up in the first place.. =/ I am still wondering if there any real gains/losses from switching from one to the other or if there are any... >Also, in the 165, is there an equivalent to the VE tables as in the speed >density stuff? I didn't see anything in CATS function list other than "Mass >Air Flow vs. RPM, (Diag)" and the injector flow rate constants. That all I saw when I looked into the CATS... I use GMEPro tho.. Rick ---------------------------------------------------------------------------- To unsubscribe from gmecm, send "unsubscribe gmecm" (without the quotes) in the body of a message (not the subject) to majordomo@lists.diy-efi.org
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