in relation to? what does 0, 64, 128, 192, etc... represent? i understand it's a voltage signal to the ecm to determine airflow. but here's my dilemma. in helping a friend burn a prom for his 383 we had to change the maf table at the 128 and 192 to get it from 150 blm to 130/130 blm/int. if the maf is translating airflow, why wouldn't it have just moved to the appropriate count? so counts would have to refer to rpm or some other factor. not just the amount of airflow across the wire. to cool it. because the cooler the wire gets the more voltage required to heat it.

 

anyone??

 

I dont have my stuff near me, but nobody is answering this so...

Those are the low RPM numbers, like near idle right? As you may or may not have seen in other posts, the MAF is an excellent device for measuring airflow at steady state, and usually somewhere near its capacity. At low RPM's and non steady state the MAF doesnt read well, and a modified engine with a cam (I'll just assume that 383 isnt running a tame cam) will screw up the reading at idle. It doesnt read airflow pulses well at all, and thats what you get at idle with a mild or not so mild cam. Other than that, it should be reading fairly close.

You should also, just in case, check to make sure there are no vacuum leaks.

 

we got it to idle after we changed the 128 and 192 counts. the BLM/INT are 130/130 now. and yes we have been reading the board. that's how we got the idea to change those. this board is a great help to 1st timers doing their own chips. because tunercat gives no manual or dictionary to help out. it's been a chore to get it up and running. have to buy 30# injectors to get the lean out. so, they are rpm related. is there a formula to determine what rpm they represent?

 

Its not rpm related, I was just thinking that those counts are low airflow numbers, and that would have to be at idle. The numbers themselves are kind of aribitrary, with no real correlation to reality. The code just tells the ecm what they mean, and it has to do with the airflow the MAF is really seeing and telling the ecm that. You cant just take the number and assign an airflow value to it, if the MAF is modified or in a different location, or any number of other things, it can skew the readings and you get to start over.

 

the mad does not translate airflow. basiscally the maf put out a Voltage for a given airflow. this Vout goes into a A/D ( analog to digtal converter ) the MCU cant understand volateg so it has to do this. so now we have

airflow thru maf. maf puts out voltage,volate goes to ecms a/d converter.

ok now for every voltage the a/d puts out a count. for insatance

( exapmle only )

at 1 volts the a/d converte puts out 111counts

now the ecm uses those counts to say ok 111 counts means
x airlfow

so now lets go back to the begining.

air goes thru maf, maf puts out Vout, Vout goes to A/D converter, A/D converter sends digital output of x counts,computation truncaites count to airflow, ecm calcutlae fuel injector pulsewdith based on counts. all of which is based on the maf tables. the ecm uses those tables as a fast way to look up ariflow to base inj pulse width.



got that ?? if not just keep asking questions. ill dig around i posted a maf airflow chart not so long ago with the maf vout to a/d counts vs airflwo not so long ago. look back thru the posts. should be a post called maf airflow.

 

thanks for answering. a little clearer now. i have that voltage chart you are talking about. i saved to my computer. now here's a question. if more air is coming in, then the wire is using more voltage to keep hot. so, why would you need to modify the MAF table? shouldn't it just move to the corresponding counts? to get this 383 to richen up at idle, we had to modify the 128 and 192 counts to go from 150 BLM to 130/130 BLM/INT.

 

well maf sensor seem to suffer from an incositancey in flow rate. changing the induction will affect the way the airflows thru the maf. thats for a stock setup. the chart i posted. but what it does give you however is the maf vout to counts which is really important when you rtrying to tune. you can look at maf vout and see what table and how many counts your at. so now you can make a logical decision to figure in for airflow.

so if vout is 1.2v's and the counts are 12345 = table 3

so now you can got directly to the table look up the grms/sec being used and adjust.

but what is really kewl it that now you can use a larger maf BS the injector constant a bit IE make it smaller then it is. and then rescale the maf tables by using the above method and get correct fueling without hitting the 255grms.sec code limit. did you follow that last one ?

 

now where do i find the MAF Vout. by using a voltmeter to which wire. or a scanner. my otc4000e doesn't show MAF volts

and i got what you said in the last sentance.

 

there should be a brown wire with a white stripe comming out of the maf. im not looking at a pinout of the ecm right now but use the incoming maf voltage to the ecm if you want.the vout to counts chart is in with the maf airflow chart i posted.

 

makes sense guess i could've looked at a wiring diagram.