MAF and speed density relationship

[Sparky2263]

MAF sensor does exactly what is described. It calculates the mass of air flowing through the sensor by means of "hot-wire" technology. That is, temp, baro, engine speed, etc. don't matter as the MAF sensor measures the exact mass of air. It is done by means of maintaining the wires at "x" temperature. The more air flowing across the wires, the more amperage required to keep it at "x" temperature. The amperage is a direct correlation to air mass passing the sensor.

Note the "hot wire" sensor is a "sampling" type of sensor. That is, it doesn't measure the whole of the mass going through it, it only measures a sample. The size and shape of the body the air is flowing through is the other measure in the calculation. That's why you'll always hear guys like me advising against modifying MAF sensor bodys. De-screening especially. That screen is what makes the sampling rate so exact. Remove the screen, introduce turbulence, skew the sampling rate.

The "hot wire" is also why those equipped with oiled filters need periodic cleaning. It doesn't take a rocket scientist to figure out that oil on a "hot wire" is also going to skew the readings.

Now, what happens if I unplug my MAF or it goes out while driving? That's where the speed density calculations come into play. I'll let GM explain that one......

"Three specific data sensors provide the VCM (http://motoralldata.com/alldata/MOTOR~V41355206~C33155~R0~OD~N/0/70910848/78153753/78153754/78154037/34853741/34857029/34857030/101367125) with the basic information for fuel management portion of its operation. That is three specific signals to the VCM establish the engine speed and air density factors. The engine speed signal comes from the distributor (http://motoralldata.com/alldata/MOTOR~V41355206~C33155~R0~OD~N/0/70910848/78153753/78153754/78154037/34853741/34857029/34859584/58948514) high resolution circuit. The VCM uses this information to determine engine speed (RPM) . Air density is derived from IAT (http://motoralldata.com/alldata/MOTOR~V41355206~C33155~R0~OD~N/0/70910848/78153753/78153754/78154037/34853741/34857029/34857030/101367128) and MAP sensor inputs. The IAT sensor measures the air temperature that is entering the engine. The IAT signal works in conjunction with the MAP sensor to determine air density. As the intake manifold pressure increases, the air density in the intake manifold also increases and additional fuel is required. This information from the IAT and MAP sensors is used by the VCM to control injector pulse width.

The speed density system is only needed when there is a Mass Air Flow (MAF (http://motoralldata.com/alldata/MOTOR~V41355206~C33155~R0~OD~N/0/70910848/78153753/78153754/78154037/34853741/34857029/34857030/56191599)) sensor malfunction. If the VCM (http://motoralldata.com/alldata/MOTOR~V41355206~C33155~R0~OD~N/0/70910848/78153753/78153754/78154037/34853741/34857029/34857030/101367125) detects a malfunction with the MAF sensor circuit, the VCM will default to speed density fuel management."

(Courtesy GM)

[Badco]

Question for you Sparky.

When I disconnected my MAF trying to chase down some pinging problems, I noticed that truck felt MUCH more responsive, quicker and sure as heck shifted with some attitude. It would bark the tires when switching gears (automatic tranny). While the MAF was disconnected it was referencing to the speed density default according to your post, which still allows for proper fuel adjustment, but how precise can it be? I am assuming more fuel was being added to the mix thus giving me more power than normal. If it is precise enough, and the ECM uses a speed density calculation in lieu of a faulty or disconnected MAF, why don't we all just disconnect our MAF for increased performance?

[1993blazerlt]

Question for you Sparky.

When I disconnected my MAF trying to chase down some pinging problems, I noticed that truck felt MUCH more responsive, quicker and sure as heck shifted with some attitude. It would bark the tires when switching gears (automatic tranny). While the MAF was disconnected it was referencing to the speed density default according to your post, which still allows for proper fuel adjustment, but how precise can it be? I am assuming more fuel was being added to the mix thus giving me more power than normal. If it is precise enough, and the ECM uses a speed density calculation in lieu of a faulty or disconnected MAF, why don't we all just disconnect our MAF for increased performance?

Speed density can work fine as the only means of calculation, All TBI and some TPI engines used only speed density setups from the factory.

[Badco]

Well I have a '98. I realize that the speed/density is a backup for me, but is it precise enough for constant use?

[1993blazerlt]

Well I have a '98. I realize that the speed/density is a backup for me, but is it precise enough for constant use?

yes it is, in the past GM has had speed density only cars, like all the s-10's before 96 and the 90-92 f-bodys

[Tink]

So what happens when you change the air intake, like the kit from poweraid?

And, why doesn't the C5 ZO6 have a MAF screen? From what I have read, tuning techs were also concerned about this situation before tuning the twin turbo engine in the C5 ZO6... but said that there appears to be zero operational problems with the screenless MAF on the twin turbo C5 ZO6 engine.

[Badco]

So what happens when you change the air intake, like the kit from poweraid?

And, why doesn't the C5 ZO6 have a MAF screen? From what I have read, tuning techs were also concerned about this situation before tuning the twin turbo engine in the C5 ZO6... but said that there appears to be zero operational problems with the screenless MAF on the twin turbo C5 ZO6 engine.

I'm talking about a complete MAF removal.

[rat]

Well I have a '98. I realize that the speed/density is a backup for me, but is it precise enough for constant use?
Yes, i haven't run a maf on my '00 since the middle of the summer.

Since you have an automatic i would recomend a vacuum modulator conversion, the stock computer has a little bit of trouble calculating engine load without the maf. This messes with the line pressure. I didn't like how mine jerked into drive when cold.

You may also notice it can be very lean at startup. I am not sure about a stock truck, but i know the way i have my ve table configured the first few minutes i have to be easy on the throttle due to lean spikes.

You will also throw an ses. A tune can get rid of that. If you have obd2 testing for emissions you can turn it off so that the computer sees everything as ready. You do need to know that speed density doesn't know to add more fuel at wot if you have a heavily modified engine, you will probably be lean. If you are to that point you are probably lean with the maf anyhow. Edit: Also you will notice your fuel trims fluctuate a little more than normal with the weather. If you tune at 60*, and get 0- -5% fuel trims you will probably notice 0- +5% fuel trims when it is 90*, not a real big deal in my opinion.

The reason you have such good throttle response is probably due to several factors. One being you might have a dirty maf, oil over the wires or something. A maf on the way out could also cause these symptoms. Or if you have some engine modifications that alter the way the maf reads. The Speed Density calculations are in there for transients. The nature of the maf doesn't make it good for reading changing amounts of airflow. Sd is great for this.

Fyi: Chryslers still use Speed Density on their product.


As far as the maf screen it can be tuned around. I am guessing the turbo kit mentioned didn't make much power, because there is a major mass air flow limmit as far as what it can measure. I think it is about 512g/sec or so. Many of them go to 2/3 bar speed density setups to go around this problem. They have custom os's specificaly for this for the ls1 crowd.

[Maximus]

TBI and CPI both are speed density systems.And the Fbody was on and off again with the MAF through out the years.If you bought one with a MAF TPI system you were already looking for a way to get rid of it because of all the faulty MAF's that were showing up on F bodies.And the cost to replace the piece of junk was crazy high.So most switched theirs to a speed density setup to get away from these problems.Most F body sights have a sticky for a How To switch to speed density setup.I prefer speed density for it's simplicity but GM and most car makers prefer MAF for it's more accurate fuel monitoring in all conditions.But sometimes simplicity can be the better choice.Which is why I still like my TBI setup.It is simple and very easy to trouble shoot when problems arise.But again both have their pros and cons.

[Badco]

Thanks for the info from everyone!

When I was messing around with the MAF that was on the blink, it did shift hard at first and gradually relaxed a bit, but it still shifted harder than normal. I assume that was from the lack of MAF signal to help with the engine load and line pressures. That explains that.
I don't run with an oiled filter for that particular reason of it potentially causing problems with the MAF.
Even when I had a new one installed, the performance difference was still evedent when running without compared to running with a new MAF.
I don't have a heavily modified, or lightly modified, engine. It's just got the freebies done to it for the most part. I guess I shouldn't worry too much about the lean conditions yet.
Thanks guys! :cool:

[badasS10]

Does removing the MAF completely and running my custom short ram on the speed density program mean it should benefeit from the increase in air flow? And will SD adjust air/fuel ratio to compensate for more air? or will I be losing mileage? Just wondering.

[rat]

Does removing the MAF completely and running my custom short ram on the speed density program mean it should benefeit from the increase in air flow? And will SD adjust air/fuel ratio to compensate for more air? or will I be losing mileage? Just wondering.
Maf or non maf it should run the same. If it doesn't there is something wrong with either the tune, or a sensor. Without the maf you will probably notice your fuel trims are much more temperature dependant.

[badasS10]

so other than the SES light, there's no problem with running with no MAF(totally removed from the intake)? Or will there be something I notice the longer I run without it? And by fuel trims, does that mean at colder temps I should see a gain in mileage, as opposed to warmer ones where I lose a bit? I'm a bit confused on the whole speed density program and how it works.

[rat]

so other than the SES light, there's no problem with running with no MAF(totally removed from the intake)? Or will there be something I notice the longer I run without it? And by fuel trims, does that mean at colder temps I should see a gain in mileage, as opposed to warmer ones where I lose a bit? I'm a bit confused on the whole speed density program and how it works.
Fuel trims are what correct your air fuel ratio. I use them for tuning personaly. So if i do a data log in the morning i will get a little different numbers than in the afternoon. You won't see different fuel economy due to this.

If you have an auto you should put a vacuum modulator in.

This is a fairly good overview of how speed density works if you like equations. It doesn't neccisaraly apply to s10's: http://www.megamanual.com/ms2/tune.htm#ve
http://www.megamanual.com/v22manual/mfuel.htm#equation

[Mikz86TA]

Very informative thread here! =) So answer this. A couple years ago I was looking at the bolt-ons for the 4.3 S. In looking at aftermarket MAFs, I was floored by the pricey units availible. I found that Granatelli made and sold just the replacement ends #350000. Being they were under $100.00 I jumped on a set. After some miles with them on I threw a SES light. I continued on not paying much attention. I got a scanner and checked the code and erased it. It was a Bank1 lean/Bank2 lean. This went on for a while and I finally put the stock ends back on. There was a noticable initial improvement but I didnt order a new truck to run around with a SES lifgt on. I kept stock until I found a used Cold-Air tune MAF for cheap on E-bay. I learned the hard way what a 'lean' condition does to a catalytic converter. Hence why theres a Magnaflow cat on it now. From my understanding the Granatelli unit I know have has the same ends and a GM electronics bridge, but has been re-calibrated for the flow of the ends. So what is the change made to the GM center to adapt the flow rate of the ends to not go lean? Every now and again I get a rich condition with the current setup, but I am unsure if its the MAF or Y-pipe that eliminated the pre-cat. It isnt so rich that I can smell it. My 355 T/A with a 750 BG Demon:2000-pont --well thats rich--I have a pretty good nose for that! I still have the #350000 ends if anyone is interested in them for a custom rod. Also another question is, why isnt there a MAP sensor mod or part to change the output for a fuel-trim change? Seems like if thats what is doing the calculating then it would be a good bolt -on part to swap and be re-calibrated if needed. Food for thought:new_micro

[rat]

You don't want to mess with the map sensor, there are no gains to be had by doing that. It needs to know the proper vacuum to know what cell to reference in the ve table.

As to the maf, don't mess with that either. As you know they can be finicky. Part of the reason i got rid of mine. For a while i ran the larger lt1 maf, it was ok, i had to tune for it of course. I wouldn't waste my time with granetelli with the cheep lt1 maf available to me.

If you want to change the air fuel ratio tune the computer.

[badasS10]

what's a vacuum modulator?

[87wildside]

It's in the trans, controls line pressure.

[rat]

It replaces the stock epc solenoid. The stock computer uses the maf to determine load on the engine, and what line pressure to command so the trans won't slip. When you remove the maf the computer has a hard time estimating the load.

[Mikz86TA]

What are some easy-to-use and good programs to tune the ECM/PCM? Ive heard of the ones for your laptop and the data cables to go to the ODB2 connector. Are they worth the price?

[rat]

Tuner cat is what i use. You have to buy a road runner to get it now though at moates.net

For '98+ you can use jet dst, or efi live

For '01+ you can also use in addition to the above you can also use hptuners, or ls1edit.

If i had a '01+ i would probably go with hptuners.

[Maximus]

I have used both LS1edit and HpTuners and I think they are both awesome software products.But I have found that with my TA using HPTuners is easier and is well supported to.But LS1edit has a huge community to support it besides the designers to.So it's almost a toss up to me.But I am a little happier with Hptuners than I was with LS1 edit.Go to both sights that has current members and just do some research on which one you think you would be happier with.Price wise they are both about the same.I know little about Tuner cat except what has been told to me but several people have talked pretty highly about it.Call them to if you want to.The two that I have dealt with were both very great people to deal with and willing to inform you and help you out.When I first started using HPTuners I was on the phone with them about every other day and they were patient and great at helping me out.

[Mikz86TA]

Ok since I got a good crowd here for input, what are some of the benefits I will see? Is there a OEM tune setting it will remember for a fall back in case needed? Can I see real-time info from the sensors/etc.? What are my tuning options? Do I need to re-boot the OEM tune from the JET programmer before I use the HPTuner? How much will this system cost me? THX for the help guys

[87wildside]

I assume all this apllies to OBD 2? First gen trucks need a custom Prom, right?

[rat]

Ok since I got a good crowd here for input, what are some of the benefits I will see? Is there a OEM tune setting it will remember for a fall back in case needed? Can I see real-time info from the sensors/etc.? What are my tuning options? Do I need to re-boot the OEM tune from the JET programmer before I use the HPTuner? How much will this system cost me? THX for the help guys
What kind of jet tune was it? I would probably start from scratch.

What i do when i tune is i download the stock tune, and save it in about 3 different places. Then i save it as something else, and i use this one to modify. Anytime i put a new tune in my computer i first download the one that was in there. I save it as whatever the date is. So i have a tune i can go back to if need be. It also tests the comunications. You can fry a computer by tuning it. But you can't fry by reading(at least for jet/tunercat).

Hp tuners is 500 last i checked. www.hptuners.com It comes with the scanner to let you see your sensor data, and it puts it into histograms to help you see where you need changes. It also has 0-5V inputs for a wideband.

Efilive is more expensive, but they have a standalone tuner available. It allows you to datalog on it, and put up to 3 i think tunes into it. Then you can plug it into your desktop computer, and edit the tunes, download the datalog etc. Nice if you don't have a laptop.

LS1edit doesn't have the fancy scanners as the above. And they don't have any custom os's. But it will get the job done. You will need to buy a scanner seperate.

Jet Dst/tuner cat is like ls1 edit in that it doesn't come with a scanner, and there are no custom os's. MxScan is available to datalog and uses the hardware. It is only $69. It has no histograms, so you have to come up with spreadsheets if you want to organize your data. It allows you to log a wideband as well.

As far as what you will gain depends. I know for me i need it because i have different injectors, cam, ect. My truck wouldn't run on the stock tune. By tweeking timing, and fueling a little you can see some gains. It is also handy to be able to change tire sizes, turn off codes, ect. And having a scanner is really handy for diagnosis.

[Maximus]

You can also disabe EGR,If an AT you can adjust TQ management and with RPM shift.Even late model LSX based F bodies ad GTO's with a manual came with damn TQ management.There are several tables you can change.I dont even have the oriinal tune that came with my TA.But there is no way possible to ever run it on my car since there is nothing stock left about it.Hell im still learning.If it wasn't for some firends and their wieband my car would run like crap right now.After I put new injectos in last month and a new cam I couldn't get the car to run right at all.If not for my friends it still wouldn't be running right.And LS1edit costs almost the same as HPtuners.Here is a run down. Item

Price Each

Total

LS1/LS6 PCM Editor/Programmer Package, locked to 1 PCM

$450



1-year Update Service (1st 6 months from purchase, are free)

add $50

Each Additional PCM (can add up to 3) (You MUST also purchase the update service if it has been more than 6 months since your initial purchase, or more than 1 year since your last software Update Service purchase.) add $100 each Handling fee, applies if you ONLY order an additional PCM license

(there is no handling fee if this order includes the LS1/LS6 base package)

add $50

[Mikz86TA]

Hmm--Great info and thanks. I believe it will be a way off until I do it but I like to research stuff in advance. Id like to see real-time data now, but with just the external mods done I think the JET plug in I have is sufficient for now. I was reading about the TQ management you listed a while back. In the S-srries it only applies to Autos right? I have a '03 4.3 5sp. The JET tuner is the plug in and load the pre-settings on octane levels. Has a custom tune but its not really that 'custom' if you ask me. It also has corrections for gear swap, tire swap, top-speed cutoff and RPM limiter adjust. I havent messed with those yet. Only the speed limiter. I will be doing 255-50-16s on the back soon so I will use the tire adjuster then. Now I have the new Y-pipe it feels like it revs easier to the redline, but Ive only hit the rev-limiter when doing a burn out. And I dont do that very much anyway. Thanks again and sorry I hi-jacked the thread

[Dogsofjune]

I was reading about the TQ management you listed a while back. In the S-srries it only applies to Autos right?
Not entirely.

[Mikz86TA]

???? oh yeah--fill me in pleaseNot entirely.

[Dogsofjune]

I have tabs under "Engine" as well as "Transmission" for Torque Management.
Though I don't see much need to monkey with the Engine Torque Management

[1badzq8]

what does it help if you take the maf sensor off also can i cut out the screen and my truck still be reliable enough for a dd

[04silveradomykk]

also can i cut out the screen and my truck still be reliable enough for a dd

leave the screen on, here are two readings of MAF signals... the screen is just to straighten the air flow as it moves over the heated wires in the MAF... removing the screen allows turbulent airflow and the trucks computer cannot make immediate correct air/fuel ratio corrections

http://www.marketitright.com/ss/tuning/MAFvsD-MAF.gif

these examples are from a 2000 5.3L,should be the same MAF for the S series, and it's the same one on my 4.3L in my fullsize

[rat]

what does it help if you take the maf sensor off also can i cut out the screen and my truck still be reliable enough for a dd
A well tuned maf, and a well tuned Speed Density setup will have similar performance. Unless you can't get a maf large enough, but for a 4.3 you aren't going to get close to this unless you start pushing around 600+hp.

I am considering throwing my maf back in now that my tuning methods have improved. i have to fix a fuel pressure issue i am having first though.