Mike Rolica Plant A, Magnesium Products Division Strathroy (519)-245-4040 Ext. 265 -----Original Message----- From: Bruce Plecan [SMTP:nacelp@bright.net] Sent: Thursday, June 15, 2000 3:56 PM To: gmecm@diy-efi.org Subject: Re: Changing 165 fuel delivery was "General tuning question -fuel economy" > Ok FROM WHAT I'VE FOUND mass air is a direct measurement of the amount of > air going into the engine. Nope, it's a calculation, Just the electronics to it are self contained rather then a MAPs where it's done in the ecm. It references MAF to a voltage drop, this voltage drop assumes the humidity is a constant. Also, assumes the O2 percentage is a constant. Both are errors, if it was accurate there would be no need for feedback. Just cause something is called something don't make it so. Look at the knock detector, it's not a knock detector, it's a noise detector tuned for a common freq. of knock. If they were as they claimed life would be a piece of cake for tuning. If the MAF and injector calibrations were right, then you would never have to change any of those variables. All you'd ever need to do is pick the right MAF for the HP level of the car, and it's matching injectors, and ecm. Guess what don't work out like that for the gm's. Yes BUT those errors are fairly small.. the blm is ito make up for humidity and crap... what I'm saying is that if an engine's flow charachteristics are changed.. maf will still tell you the amount of air going in with the same error that it did before the mods... with map, eveything goes out of whach...... map is based on pressure drop... plain and simple.. you said yourself that vacume or pressure changes in a modified engine.. snip > 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.... Assuming the MAF theory was accurate, and since it's not then tinkering is needed. Changing Air Filter Types can effect the MAF since the turbulence of the air going across the wire changes. > For map since the ve represents the cd of the motor... different motors will > have differing cd's MAP has to be tuned to a specific engine, yes. cd?. CD coefficient of discharge. > 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... Have you hooked a scope to see if the MAFs output is capable of reading a high gms/sec?. If you have what did the numbers do, if you don't mind sharing. Tested the maf on a flow bench hooked up to a 52mm tb and plenum.... Got maf to put out fairly linear from 0 to 10v.... think 10 volts was some where aroun 600g/s...I'll have to check. So yes it is capeable.. > 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.. Kinda a big jump to get there thou. The MAF is always reading behind the actual flow across it other then steady state. The system is little better then Alpha-N in my book. It seems to be more like a Apha-N that fine tunes cruise mode with the MAF. That's why they can run so good for diagnostics with no MAF signal. The MAF is useless in sudden transistions. MAP is dam near real time the errors is in the diam lenght of the sensor line. 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.... as possible. As Possible varies the second you get away from the oem ducting. 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.... Motors by application. Vehicle weight gearing under hood air flow, all play a part. Grumpy Agreed..... > Mike Rolica ---------------------------------------------------------------------------- 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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