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Thread: MAF flow effects

  1. #1
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    Default MAF flow effects

    If you were to increase the flow across the MAF sensor what effects would it have over the numerous interlinks (injector volumn, EGR valve position, timing etc.) in the PCM?

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    Surely someone has some idea of what would occur.

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    It will defuel sooner. The actual air volume would be less than the perceived, so it would "think" it has too much air for the fuel/power output. EGR position would not likely be effected much, if any, but could go nuts 'cuz the output doesn't match the input. It's a delicate balance, and if you lie to it w/o computer intervention, it'll throw a fit (SES, limp, etc.).

    Bad idea.
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    It is not clear to me what you mean by 'increase the flow' across the sensor ? ?

    Do you mean that you would somehow 'trick' the sensor into sending the same signal it does now at higher flow rates? Why would you ever want to do that?

    The MAF is a Mass Air Flow sensor - it corrects for changes in air density due to humidty, altitude, and temperature to give an accurate measurement of the mass of air flowing [Kg per minute, etc.] in order to meter the proper amount of fuel through the injectors to maintain the correct air-fuel ratio.

    If what you mean is to physically increase the flow by removing restrictions, etc. then there should be no problem as long as you do not exceed the range of air flow that the MAF sensor was calibrated for. Not all sensors are universal - many have upper and lower limits, too high or too low and you will not get accurate readings.

    The MAF is one of the crucial inputs to proper fueling of any engine - it would be the last thing I would ever mess with.
    Jeff

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    Quote Originally Posted by DmaxMaverick View Post
    It will defuel sooner. The actual air volume would be less than the perceived, so it would "think" it has too much air for the fuel/power output. EGR position would not likely be effected much, if any, but could go nuts 'cuz the output doesn't match the input. It's a delicate balance, and if you lie to it w/o computer intervention, it'll throw a fit (SES, limp, etc.).

    Bad idea.
    I don't understand how if it is reading more air that it would defuel, that sounds backward but that is why I'm asking------I don't know how it all interacts, but would like to learn.
    Does it not effect the timing?

  6. #6
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    Quote Originally Posted by jmoser View Post
    It is not clear to me what you mean by 'increase the flow' across the sensor ? ?

    Do you mean that you would somehow 'trick' the sensor into sending the same signal it does now at higher flow rates? Why would you ever want to do that?

    The MAF is a Mass Air Flow sensor - it corrects for changes in air density due to humidty, altitude, and temperature to give an accurate measurement of the mass of air flowing [Kg per minute, etc.] in order to meter the proper amount of fuel through the injectors to maintain the correct air-fuel ratio.

    If what you mean is to physically increase the flow by removing restrictions, etc. then there should be no problem as long as you do not exceed the range of air flow that the MAF sensor was calibrated for. Not all sensors are universal - many have upper and lower limits, too high or too low and you will not get accurate readings.

    The MAF is one of the crucial inputs to proper fueling of any engine - it would be the last thing I would ever mess with.
    This post actually stems from another "LBZ Hot and Loss of Power", in which there were some good responses but not a lot of direction for what to do to find out what was causing such a loss of towing power.
    One response from a Banks Tech led to a phone conversation with same; and the basic recomendation was to relocate the MAF. He said that Banks had had some problems with their intake system in developement and found that when they located the MAF in the bend just before the turbo tract, and on the outside of the bend that they found good power gains and also found that the EGR valve pretty much stayed closed all the time.
    Fact or not I though it was something to check out and try; if I could get any other insight that seemed favorable.
    The position of the MAF on my LBZ (others too I assume) is on the inside of the first bend past the filter box. In this position the main velocity of course is on the opposite side of the intake tube; as with any hydraulic action the inside of any bend has a lower velocity than the outside. Depending on the configuration a vaccum can actually occur on an inside of a bend at some flow rates. (In chill water systems sometimes to the exent of air pockets and pump cavitation given the right proximity.)
    In any case it seems that Banks by their repositioning has increase the flow at the MAF dramatically. How does that work?----and is it possible that this could actually effect the EGR. Seems that the consenses here is that it could not.
    I'm still looking for the power loss----Killer Bee says I'm on a ghost hunt!!! But this ghost sure has some real power drawbacks---hot too.

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    MAF is one the better inventions for a motor. The old speed density computers back when fuel injection first came out where a table of set values that couldn't take into account environmental conditions. Those motors were hard to add performance to since back then it was hard to rewrite the ECU tables. (OBDI was the only game in town).

    Now, MAF is much better because it allows the motor to dynamically change to the environment. Messing with that signal will either cause a LEAN or a RICH Condition. More Air = More Fuel, so if you trick the MAF to report more air than is going in, then you will have RICH condition, although the 02 sensors will rat out the MAF and the motor will DEFUEL to compensate for the mixed signals. This can cause a surging motor because the MAF and other sensors are battling each other.... Same thing can happen if an onxygen sensor is going bad.
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    Quote Originally Posted by Dakster View Post
    MAF is one the better inventions for a motor. The old speed density computers back when fuel injection first came out where a table of set values that couldn't take into account environmental conditions. Those motors were hard to add performance to since back then it was hard to rewrite the ECU tables. (OBDI was the only game in town).

    Now, MAF is much better because it allows the motor to dynamically change to the environment. Messing with that signal will either cause a LEAN or a RICH Condition. More Air = More Fuel, so if you trick the MAF to report more air than is going in, then you will have RICH condition, although the 02 sensors will rat out the MAF and the motor will DEFUEL to compensate for the mixed signals. This can cause a surging motor because the MAF and other sensors are battling each other.... Same thing can happen if an onxygen sensor is going bad.
    So how does that relate to what Banks is doing in their relocation which obviously places the MAF in a much higher flow area and their claim of the improvement in power. That said, Banks is pretty well known for being effiency minded which would be contridictory to the more fuel added equation that should play a major role adversant to that end.

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    If I recall, BANKS is more than just "messing" with the MAF. It is just part of the whole equation in how it relates to the engine management system (stock or not) that creates "more power." Since, I do not know about the Banks system you are talking about it is hard for me to get specific as to why/what they are doing. Although, knowing Banks kits, I would assume that it is more involved then just moving a stock MAF to a better place - although I could be wrong.

    Easiest analogy I can think of help you. On a gasser with a distributor. The factory sets a specific timing that is realiable, dependable. You can gain a few HP (5-10 depending on motor) by advancing/tweaking the timing. Advance too far and you get denotation and pinging. Take that to MAF, you can gain some HP by tweaking it tricking the motor to squirt more fuel. However, tweak too much and you get driveability and computer issues.
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  10. #10
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    Quote Originally Posted by Dakster View Post
    If I recall, BANKS is more than just "messing" with the MAF. It is just part of the whole equation in how it relates to the engine management system (stock or not) that creates "more power." Since, I do not know about the Banks system you are talking about it is hard for me to get specific as to why/what they are doing. Although, knowing Banks kits, I would assume that it is more involved then just moving a stock MAF to a better place - although I could be wrong.

    Easiest analogy I can think of help you. On a gasser with a distributor. The factory sets a specific timing that is realiable, dependable. You can gain a few HP (5-10 depending on motor) by advancing/tweaking the timing. Advance too far and you get denotation and pinging. Take that to MAF, you can gain some HP by tweaking it tricking the motor to squirt more fuel. However, tweak too much and you get driveability and computer issues.
    Actually that is what Banks recommended that I do. After talking about my intake modification (stock air box with and additional 3" air source that draws thru the recovery hook hole) they said that I was probably getting as much air as what their cold air intake kit was getting. They said that their original design had the MAF located just past the air box as with the stock set up. They were having problems with the EGR staying open so started trying other MAF positions. When they located it in the bend just before the turbo tract they found that the EGR valve stayed closed most 100% of the time and they also dyno'd a very good gain in power. I can't see why they would have any reason to be less than honest about it. I feel that they were just trying to help me out because of the higher temps and loss of power that I experienced after installing their exhaust system---good customer support in my estimation.

  11. #11
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    Okay; from what input that has be generated here it seems that what Banks has done with the MAF, and what they suggested that I do with mine; is 180 degrees from one another. Now I hope you can see why I asked what effects that increased flow rates have on the MAF. I can't see going to the trouble of making an additional MAF port in my intact if the exercise is overtly futile; not to mention that by doing so with out some sembilance of understanding of the ramifications of the experiment. It evidently works for Banks but how in the world does it work if it is so contradictory to what I have been hearing here on this site. Need some help here!!!

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    The problem is that in your first post, I assumed that you were talking about messing with the MAF on a STOCK motor. Now that I realize you have "modified" the intake of the motor, you have created a new condition that the motor is running in. This is my fault... Sorry for any confusion I may have caused; however....

    If Banks says to move it because their intake likes it there and the motor runs better, what have you got to lose by trying it? You have issues that you are trying to correct and won't know if it works until you try it...

    What banks expereinced falls directly in line with what I have been saying all along. Change the amount of air flow or the metering of such and you could have driveability problems. Here you have driveability problems, possibly due to the aftermarket components being more (or less?) efficient than stock. GM is only gonna test and make there systems work on a stock truck, which makes sense.

    To compensate for the aftermarket components, Banks, found a spot to mount the MAF that works well... If it was my truck experiencing problems I would be relocating the MAF. Worst case is I either need to buy another intake piece or I have to plug it.
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    I also understood your question to be about a stock system, and your wanting to shortcut a performance mod.

    In your case (and Banks), what likely happened is their intake with the MAF relocated (originally) was decreasing the OEM efficiency of the MAF. Relocating (correcting) it likely replaced what was lost, and it is again more efficient and within its operational window. Taking it outside of it's operational window will wreak havoc with the PCM, as Banks discovered.
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    Sorry but I think I am more confused than ever. If the MAF is relocated from a position that is in a very low flow area of the intake tract (even possible decreasing flow with tract flow rate increase due to the probable vacumn effect that I pointed out) to a position that is obviously in a much much higher flow area, it would seem that all speculation of the MAF's reaction is out the window. I think that I heard that a de-fueling would be expected with flow increases. Also from what was offered herein I would believe that a very high injector flow rate would be seen if; 'higher flow = more fuel', my feeling is that the flow has to be near doubled over the inside the bend position. There has to be more to it than what is speculated or thought to be fact. Sure seems that the understanding of the MAF must only be within the grasp of the designers-----it sure has this country boy baffled.

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    Hmmmm.

    OK. Consider this.
    The OEM system has a known intake pipe diameter, and the MAF sensor is located in a known position within that pipe. Therefore, with some logic, it can calculate the lb/min of air traveling through the pipe. The PCM monitors the air intake volume and temp, MAP, engine load, fuel temp, TP, among others. The PCM calculates what each value should be under given circumstances. If you change one parameter, the PCM will expect to see corresponding changes in others. If any of these parameters are outside of what the PCM considers normal, it will try to correct the perceived problem. One of the first things it will do is defuel. If you operate outside of the PCM's envelope, it will defuel. An increase in air volume alone, without the presence of a corresponding fuel, MAP, or engine load change will be perceived as a problem the PCM will address. Fuel is not metered according to air intake volume alone.
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    I think that possibly there is still a misunderstanding of my intake; lets give it another try so there can't be any doubt of what it is.

    The intake tubing and billows from the air filter box to the turbo is completely stock, no change in any way.

    The air filter box is stock, with the exception that forward upper quarter around the deflection vanes is removed to provide a more direct route for the added 3" supply to flow thru.

    A 3" aluminum dryer vent is used to transfer air from the air dam hole (where the recovery hook was removed) running up and thru an enlarged hole behind the headlight and then entering the air filter box enclosure.

    The original air breathing holes into the fender well cavity were enlarged and provided about 3 additional square inches of breathing area.

    Additional sealing was done around the air box to prevent any air from the engine compartment from entering the air box.

    Thats it, a pretty basicly stock system; and really, sans the air filter box the Banks intact tract routing and size is pretty much a mirror of the stock system also.

    That cleared up--I hope; it seems a very DRASTIC change moving the MAF from an inside bend location (relatively shielded) to a point where it is getting a direct hit, if you will, from the incoming air charge. From what I have learned here that would seem to really drive things bonkers, no? That is why there would seem to be much more to the system than meets the eye or common conception of its scope.
    I notice that there are five wires at the MAF so I presume that it is sending out four separate signals to the PCM.
    1. Air flow
    2. Air temp. ?
    3. ??
    4. ??

    1. More air flow=more fuel -----provided the criteria is met?
    If more air flow is detected but load is light what happens?
    In a gas engine a lean mixture equals more heat many times, is it the same with a diesel?
    2. Air temp ??? what does the PCM do with that, if indeed that is one of the MAF signals?
    3. & 4. Can't ask the question because I don't even know what they are or if they exist.

    Bottom line is, I don't mind modifing if I've some grasp as to the workings of what I'm modifing----but in this case it is evident that I don't have a clue. Also it might even be entirely on the wrong track toward correcting my elevated EGT's, water temps, and loss of towing power.



    Still need help guys!!!!
    Last edited by moss6; 09-13-2007 at 17:10. Reason: add

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    5 wires. 1 ground, 2 each for the temp and velocity, or something like that. Maybe 1 and 3. I could dig up the diagram, but it's pointless.

    If the PCM "sees" more air passing through the intake, it WILL NOT add fuel because of this. It may expedite fueling from idle, if it detects the airflow sooner than OEM. Still, several other input values have to be "seen" before more fuel is added. If the PCM "sees" more air, and can't make sense of it (no other input values changed), it will assume an error.

    Changing any part of the intake system can (not necessarily will) change the dynamics of the airflow. Making more air available to the intake by modifying the tract can increase the perceived MAF. It won't, however, increase fueling in and of itself. More fuel is "requested" when you increase TPS input, but you won't get it if all the other input values aren't in line.
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    Great input that, thanks! Don't know what TPS is though, help.

    Another question; what effect do you think that the MAF's orientation to the the direction of flow has on its readings. That is that Banks recommended that the MAF sensor be rotated 90 degrees from its original orientation to the flow in the intake tract. Could that be something that would offset the drastic change in the amount of flow with the new location in the intake tract?
    Also does it seem possible that the relocation could make the EGR stay closed?
    And one more does a lean mixture in a diesel create more heat as it does sometimes in a gas engine?
    Last edited by moss6; 09-13-2007 at 17:58.

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    Quote Originally Posted by moss6 View Post
    Don't know what TPS is ...
    TPS - Throttle Position Sensor

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  20. #20
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    I guess that makes sense in the relation to the loss of power, as load is increased throttle position has to be linearally greater to maintain a given speed. If flow across the MAF does not correspond then additional fueling is not provided????

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