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Old 04-28-2003, 11:51 AM   #1
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Exactly what does the ECM read in from MAF sensor?

Is the signal from the MAF to the ECM a DC voltage OR is it in COUNTS?????

In the 165ECM tables ($32b), the MAF tables are COUNTS and air flow in gms/sec. Where is the conversion to COUNTS made? (in the ECM or in the MAF)? This of course ties into the first question.
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Old 04-28-2003, 01:03 PM   #2
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Re: Exactly what does the ECM read in from MAF sensor?

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Originally posted by doc
Is the signal from the MAF to the ECM a DC voltage OR is it in COUNTS?????

In the 165ECM tables ($32b), the MAF tables are COUNTS and air flow in gms/sec. Where is the conversion to COUNTS made? (in the ECM or in the MAF)? This of course ties into the first question.
Can be either frequency (counts) or voltage. Although I don't know if frequency based MAFs were ever used on 3rd gen f-bodies.

See this thread for a run-down of how the MAF code works:

http://www.thirdgen.org/techbb2/show...hreadid=114856

RBob.
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Old 04-28-2003, 01:06 PM   #3
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I thought the v6 maf was frequency based?
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Old 04-28-2003, 01:59 PM   #4
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maf voltage goes into the a/d converter. its translated into counts. the maf table basically correlates counts to grams/sec.
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Old 04-28-2003, 02:14 PM   #5
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I know that my '99 MAF is frequency based, while that my '87 MAF is voltage based.

What I was trying to get at is: for the '87 MAF, where is the a/d converter located in the physical sense? In the ECM or in the MAF sensor itself?

If I put a voltmeter on two wires from the MAF (the correct two whatever they are), will I read a voltage?

Rbob, when the MAFs came back on the F-body (I dont know the exact model year), they were all frequncy based to the best of my knowledge, and the upper limit is now 512gms/sec.

The ultimate purpose of my question is that can I alter the DC signal from the MAF and in effect change the scale of the MAF tables. I know that the ECM will not recognize a value bigger than 255, but maybe I can scale other tables to meet 14.7 AFR at part throotle and 12.8 at WOT.
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Old 04-28-2003, 02:32 PM   #6
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the a/d converter is onboard the ecm. its a basic 8 bit model. it can read from 0-5 volts. but what i dont understand is hwy gm handicapped the MCU's ability to read it. oviously it should b able to read upto 255 entrys. do you see 255 Maf table entrys in all 6 tables combined ?? i think fixing that problem will really help the issue. once i get the whole fueling calculations with all of its verys ram cals etc. i should be able to re index the maf tables to use those unused entrys.
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Old 04-28-2003, 04:11 PM   #7
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Quote:
Originally posted by doc
I know that my '99 MAF is frequency based, while that my '87 MAF is voltage based.

What I was trying to get at is: for the '87 MAF, where is the a/d converter located in the physical sense? In the ECM or in the MAF sensor itself?

If I put a voltmeter on two wires from the MAF (the correct two whatever they are), will I read a voltage?

Rbob, when the MAFs came back on the F-body (I dont know the exact model year), they were all frequncy based to the best of my knowledge, and the upper limit is now 512gms/sec.

The ultimate purpose of my question is that can I alter the DC signal from the MAF and in effect change the scale of the MAF tables. I know that the ECM will not recognize a value bigger than 255, but maybe I can scale other tables to meet 14.7 AFR at part throttle and 12.8 at WOT.
Yes a voltage from the MAF, ADC is in the ECM. The older freq based MAF are a low frequency output. Something like 30Hz to 150Hz or such. The newer MAFs (LT1 & LS1) are not only larger but the output frequency output is also higher (somewhere around 2Khz to 12KHz range).

Before I played too much with the older voltage based MAF I'd want to test it to see if the output really even reaches the 5 volt level.

The output of a MAF flattens out as the airflow increases. Due to this I would be tempted to use an LT1/LS1 MAF and convert the frequency output to a voltage (LM2907) and plug that into the ECM.

Will have to re-calibrate all of the MAF tables, but no big deal. Can also play games with the code. Such as make the gms/sec value half, so that a value of 100 is 200 gms/sec. Then double the PW once the calc is done.

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Old 04-28-2003, 04:41 PM   #8
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id like to figure out how to add those tables. rbob i need help. as for fooling the code. i was just gonna redo the variables that calcualte inejctor pw. effectively BSing the ecm but at least you should be able to input the actual injector size. i was also gonna undertake making the correct MAF tables for those bigger mafs. so all one would have to do is input the injector constat use the correct MAF anf then diddle with timming. yes i figured on fixing the lv8 calcs as well to go with the bigger maf so the timming falls correctly where it should.
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Old 04-28-2003, 06:07 PM   #9
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Quote:
Originally posted by RBob
The output of a MAF flattens out as the airflow increases. Due to this I would be tempted to use an LT1/LS1 MAF and convert the frequency output to a voltage (LM2907) and plug that into the ECM.

Will have to re-calibrate all of the MAF tables, but no big deal. Can also play games with the code. Such as make the gms/sec value half, so that a value of 100 is 200 gms/sec. Then double the PW once the calc is done.

RBob.
Point
RBob, I am not a hardware guy. Are you suggesting a modified MAF were the the MAF ultimately outputs 1/2 the voltage it normally gives thus actually doubling the total CFM it is able to register at 5 volts? AND, just altering the PW to half it's normal value to compensate for the doubled MAF? AND then simply tweaking the MAF Tables? Like some guys use a 2 Bar Map on a 7730 and cut the PW in half?

Logically, it all makes perfect sense. So how does one create or modify a MAF so it can register double the CFM for a given voltage (let's call it a MAF2x). Does this technology exist? It really doesn't sound that it should be that hard. (though it may require some co-operation between a MAF mfg - the software doesn't sound like anything major to overcome.

If currently, 255 (in the ECM) = max CFM of 1xMAF @ 5V. A new 2xMAF has 255 = 2xCFM @ 5v. Maybe 3xMAF has 255 = 3xCFM @ 5V. Heck MAYBE a 4xCFM. Why stop at 2x? Don't make that the NEXT limitation.

Ignoring any possible "graininess" due to the doubling/tripling/quadrupling of the CFM reading for a given voltage; if the hardware existed, it doesn't seem to be a very hard "fix" in the BIN by altering the PW. Guys have done this on 7730s with boost, a 2 bar MAP and 1/2 PW. Not the prettiest, but works.

And then correct any deviations due to lack of linearity between the new Volts and CFM via the MAF Scalar Tables. Sounds quite do-able and worth looking at deeper.

Counterpoint
Does anyone remember Point/Counterpoint from 60 Minutes during the 80s? If so, the following is a counterpoint to the above point. It is intend this be slightly humorous and not directed at anyone personally. ESPECIALLY NOT RBOB. RBob stated a very effective solution for the software should a 2xMAF be created.

Sheila you stupid hag, you missed the obvious. The MAF is really only important for part throttle driving. Yes, it is wonderful to have 128/128 MAF correction in PE through an engines entire power range. But if you just tune via the PE Tables and WB for WOT, you can get your car running as close to perfect with minimal effort.

PE is PE and part-throttle is part-throttle. Let the MAF do its job while driving around in part-throttle and tune PE via the "PE %Chg A/F Ratio vs. RPM" Table with the aid a WB O2 sensor and 1,320 feet of pavement. It pratical, it's easy and it's effective.

To tune ALL those MAF tables seems like a lot of work. Now I have to go driving all around hell's half acre with a WB O2 Sensor and develop a new MAF Scalar Table. Are you sure you're not just a spy from the SD camp? Maybe that's what you call fun & excitement, but I have better things to do.

Now you've taken (MAF) a wonderful simple system and turned it into some complex monstrosity rivalling SD. If I wanted SD, I would have installed SD. I want MAF because of it's simplicity to accomplish effective tuning with minimal effort.

(Again, RBob, this is NOT directed at you in any way, I am just trying to point out to MAF users a "pratical side".)
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Old 04-28-2003, 06:18 PM   #10
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Quote:
Originally posted by funstick
id like to figure out how to add those tables. rbob i need help. as for fooling the code. i was just gonna redo the variables that calcualte inejctor pw. effectively BSing the ecm but at least you should be able to input the actual injector size. i was also gonna undertake making the correct MAF tables for those bigger mafs. so all one would have to do is input the injector constat use the correct MAF anf then diddle with timming. yes i figured on fixing the lv8 calcs as well to go with the bigger maf so the timming falls correctly where it should.
To learn the code you have to start with easy stuff. I made a lot of mistakes in learning Moto assembly and how to do things in GM ECMs. But as I did more and more it became easier and easier.

A test bench is nearly a must have. Being able to check code changes on the bench allows you to play and try stuff out.

Try making a table larger, or adding another one with a qual to switch between the two. Then try other stuff. You asked about branches in a post today (someplace here), they operate on the condition code registor. Need to check that out in the HC11 doc from Motorola.

RBob.
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Old 04-28-2003, 06:34 PM   #11
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(in reply to Glenn's point/counter-point post)

On the point side I was thinking of using the LT1/LS1 MAF which can read to 348 gms/sec (or 512 gms/sec?, not sure). It is also physically larger so it will flow better.

It is a frequency based output, so convert that to volts and plug it in (easy w/LM2907). Sure, you'll lose resolution, but the SD guys having been (and GM) doing that for years with 2 & 3 bar MAP sensors.

Could always plug the freq directly into the ECM also and putting the code in place to read it that way. Just more work that's all.

On the counter-point side I believe that once the MAF scalar tables are calibrated it would be a better system then SD. Manufactuers like MAF because the tune is more stable. Can't be because a MAF costs a lot more then a MAP sensor.

One thing about using PE for fueling once the MAF max limit is reached is that it is N only. There is no throttle opening angle input to the PW calc. So it is even worse then Alpha-N. The measurement limit of the MAF and the airflow requirements of the engine define the size of the dodo area.

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Old 04-28-2003, 06:40 PM   #12
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Quote:
Originally posted by RBob
One thing about using PE for fueling once the MAF max limit is reached is that it is N only. There is no throttle opening angle input to the PW calc. So it is even worse then Alpha-N. The measurement limit of the MAF and the airflow requirements of the engine define the size of the dodo area.

RBob.
Thanks for the answer to both the point and counter-point. I might do that more often. I love playing devil's advocate.

Aside, can you explain "N" and "Alpha-N" (or post a link if it's been discussed a gazillion times and I'm blind and missed it). I am POSITIVE that I am not the only happy camper that goes "the what-a...."?
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Old 04-28-2003, 07:06 PM   #13
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Quote:
Originally posted by Glenn91L98GTA
Thanks for the answer to both the point and counter-point. I might do that more often. I love playing devil's advocate.

Aside, can you explain "N" and "Alpha-N" (or post a link if it's been discussed a gazillion times and I'm blind and missed it). I am POSITIVE that I am not the only happy camper that goes "the what-a...."?
Alpha-N fueling is based on throttle position (blade angle) and RPM. I've also seen it as N-Alpha. Out on a limb I believe that the early Bosch mechanical systems are Alpha-N.

Tying this into the max'd MAF if always at WOT then the PE tuning works. MAF is at 255 and adding that much fuel, airflow is max for that RPM and the PE table is % change vs RPM. Wala, good fuel control.

Now lift a bit but still keeping the MAF above its max limit, say 260 gm/sec. Now the AFR is rich as the PE % change is setup for say 450 gms/sec (WOT flow) at that RPM. This is due to setting the PE change large enough to command a 9:1 AFR to get a 12.8:1 AFR at WOT.

If there were an alpha parameter to the fueling calc the lifted go-pedal could be taken into account. Hmmm, anyone for a TPS parameter to the PE fueling % change?

RBob.

Last edited by RBob; 04-28-2003 at 07:08 PM.
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Old 04-28-2003, 07:17 PM   #14
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Quote:
Originally posted by RBob
Hmmm, anyone for a TPS parameter to the PE fueling % change?

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Old 04-28-2003, 08:37 PM   #15
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So I guess this means I can use a digital maf w/ my third genner?Oh yeah, just get a maf connector for a gn and splice the existing maf wiring to it.Then use the translator and the digital maf.It's my bright idea,would it work?



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quote:
--------------------------------------------------------------------------------
Originally posted by kvu
So I guess this means I can use a digital maf w/ my third genner?Oh yeah, just get a maf connector for a gn and splice the existing maf wiring to it.Then use the translator and the digital maf.It's my bright idea,would it work?
--------------------------------------------------------------------------------



Ugh, No.
Haven't you been following the other threads where the interface is being talked about?. This thread is about the recalculating the MAF, a seperate issue from the interface. As stated you bright idea won't work. You need to go from Freq to voltage on the MAPs output.
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Old 04-28-2003, 08:44 PM   #16
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Try making a table larger, or adding another one with a qual to switch between the two. Then try other stuff. You asked about branches in a post today (someplace here), they operate on the condition code registor. Need to check that out in the HC11 doc from Motorola.
this is what ive been askign for help on. the ECM bench has been under construction for some time. funds and tiem permiting.

on a side note i have to keep something that ive ben working with a manufacturer on under my hat. to say breathing through a straw may not be a problem anymore is an understatment. no converters plug and play.

problem is i need help developing the code. thats why im asking for help. once the MAF tables are calibrated for the MAF and the injector constant values reworked and the lv8 calcs reworked then its fiarly straight forward. your back to tunning via injector constant and PE % vs RPM. plus the cold start. the hard parts is making the maf table corectly correlate. the code can stay as public as youd like. just realize the some manufactuere of aftermarket parts might be using it as well. its part of the deal. cant seperate the problem from teh code they wont do it. this is the only road i can go.

good news is there willing to make custom meters however.

rbob i need you help. this is not for profit. at least at my end. but will abosolutely be benificial to the 3rd gen community. the manufactrer only want to have the properly prepared code the send out with the MAfs becuase of some bull**** about lawsuits they had a while back. when the deal is done i still wont be able to say who has the code but i will absolutely make sure it stays in the public domain.for the DIYer

can you help ?? and id be doing this with $32b. Do me a favor Email me.
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Old 04-28-2003, 08:55 PM   #17
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We could have been futher if that one was'nt overlooked.I agree the maf system is a good system.I never had a backfire once.Rbob,why is it that a map system tends to "pop"backfire as rpms increase during a foul condition.Example,If I take off a spark plug wire and rev the motor(in park) a map system will backfire while a maf system misses.I have worked on alot of cars.If a car comes in and it backfires as rpms increase it's usually a map system(not always).Now usually when a map system bacfires like that it is in the ignition.From all the cars I worked on maf will just missfire,never backfire.It just seem the maf system is less touchy.How much latency diff is there in the maf vs map sensors?
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Old 04-28-2003, 09:03 PM   #18
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Old 04-28-2003, 09:34 PM   #19
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This is really good stuff.

I have thought about both of Glenns point & counterpoint for the last year, but have actually concentrated on tuning my '99 SS. And Rbob's idea about using an LS1 MAF and convert the freq output of the MAF to voltage is great. BTW: Since I have been tuning my LS1 car, I know for a fact that the stock MAF unit is 75mm diameter, while aftermarket units are 85mm (which I am using now). The PCM table is limited to 512gms/sec, goes from 1500Hz to 12,000Hz, and I suck in about 310gms/sec to make 400RWHP.

About our 3rd gen MAF: I have not measured the diameter , but I think they are 75mm. They flow 711CFM if modified. So, based on what 87400tpi posted elsewhere, a MAF car is limited to 547HP. If I could ever make 547HP at the flywheel, I will be TOTALLY delirious. (did I spell that right?) If we accept the 547HP upper limit, the MAF should flow plenty of air even for my planned 395cu in engine.

Also, going back to Glenns counterpoint: He is right on here. Part throotle is part throotle, the MAF will register the correct flow for all part throotle situations. You will not hit the 255gms/sec limit while at part throotle. When you go into PE, we have a table called "WOT % change to fuel/air vs RPM" to add the necessary extra fuel even if the MAF 255 limit is hit.
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Old 04-28-2003, 09:44 PM   #20
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could we switch to email ,glenn?I can let the misunderstandings go but I need to understand some things.I just don't want to stink up docs thread.Can you email me?
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