MAF-less tunes

ejg3855

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So I think if we could get the answer to why some of the OEMs don't use them and some do, we'd have the answer to why the tuners do or do not. The 2.5L 5cyl VAG engines in the current Golf/Jetta/Beetle/Passat don't have a MAF, they seem to run fine. But the VR6, the 2.0L non-turbo engine, all the turbo engines, as well as all the TDIs, do. :confused:
I am pretty sure the 2.5L uses a maf, a quick google search confirmed. Airflow is much more important to be known on gasoline powered vehicle.

Also, as far as MAFs being used for EGR checking: that may be true in some cases, however there are other methods used to verify EGR flow. Temperature sensors post-EGR valve, delta pressure feedback (DPFE) sensors, and even a MAP (on non turbos) can be used. Heck, GM used to use the oxygen sensor signal to check EGR operation. Plus, many engines that have a MAF, don't even have EGR valves


I'd suspect, its simple and reasonably cost effective to meet emissions needs? Those other sensors cost $$ and the MAF while expensive is prolly cheaper than integrating a few sensors into the system, not to mention the calibrations from Bosch are needed.
 

darkscout

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If a MAF is totally not necessary, then why do so many (the vast majority) of automakers use them?
The feds came up with 2 requirements:

1) You need to meet emissions.
2) You need to throw a proper diagnostic when you are out of emissions.

MAF meets both of those requirements.

They are somewhat fragile (especially the hot-film type, like most of our Volkswagens use), kind of expensive, and in pretty much every case where they are used there is also the other sensors that can be used to "calculate" the air flow using math instead of actually measuring it.

Every single one of the road-going diesel engines under 10k GVWR use a MAF sensor.
Emphasis mine. On highway was the first to get the emissions regulation. At that time a MAF sensor met all of the requirements. And while 200k miles is plenty long in the on highway world under 10k GVWR when you're talking about running a diesel 24/7 for years it isn't. Which is why a lot of the other manufacturers didn't go with them.

Could this be a conspiracy for Bosch to sell more MAFs?
Who makes the MAF?

Keep in mind, Caterpillar does not [yet] need to meet the emissions requirements that Volkswagen does, since they are not building anything that small that is roadgoing.
Emissions are HP based and they do have them just not in America.

So to that end, it would seem a MAF is a very integral part of an EPA-compliant emissions friendly engine management system.
This would be for offroad use only. Obviously. Like everyone else in this subforum.
 

ejg3855

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I thought that the MAF only reads so high and many turbo upgrades can pull more air than what they can read?
I don't know about tdi's but I know this is very much true in the 1.8t world.

excuse my grammer, Google thinks it knows what I want.
 

GTiTDi

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IMO, it's just another sensor to fail on you at some point...deleting it eliminates that failure point and is that much closer to the M-TDI ideal ::)...if you can have your tuner delete it and maintain an efficient fuel curve based on boost..then list it on the classified forum ;)
 

darkscout

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Do the new cylinder pressure glow plugs fit into the old head? (same thread). Because you could really nail in a tune with those.
 

burpod

teh stallionz!!1
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from what i heard, the CR glow plugs aren't the same height. but i think the BEW 5v steel plugs fit the same. i would love to be able to use those (with pwm) in my AHU cars.
 

robnitro

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I thought that the MAF only reads so high and many turbo upgrades can pull more air than what they can read?

The stock tdi maf is only saturated if you run more than 30 psi or so and thats at 4k and up.
Maf reporting in vcds is in mg/s but thats derived from abolute flow (kg/h or lb/h) divided by strokes per hour..giving you mg/s.

Same 1000 mg/s at 2k and 4k... at 4k maf is reading double the x kg/h.
 

KERMA

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Interesting discussion

In my opinion, maf sensor and map sensor are two different ways of accomplishing the same thing.

What everyone calls a "smoke limiter" is really just another "torque limiter" with a different name. The goal of this extra torque limiter is to hold back fueling under certain "low air" conditions to minimize the visible smoke, but allow full fueling (torque) when sufficient air is available. In OEM factory applications, generally it's intended to have influence only under certain part-throttle or transient conditions. So, you could call the "smoke limiter" a "part throttle torque limiter" and it wouldn't be incorrect.

If a smoke limiter is too restrictive, then you get more of a "laggy" feel and the response is overly dependent upon the turbo being able to spool. (generally speaking of course)

If the smoke limiter too loose, you get that low rpm smoke associated with "pre-spool" conditions. This smoke can vary in intensity. (Side note: "acceptable" smoke seems to be HIGHLY subjective and individual)

I've personally done lots of tunes over the years with map based smoke limiters, and lots with maf-based.

Generally what I've found is that the maf-based smoke limiter tends to be more resilient and robust under a wider variety of environmental conditions. In other words, you get a tune dialed for a particular combo of injectors/turbo/IP and it still behaves in the summer and winter, high altitude and sea level, heat soaked and cold.

The MAP-based calibrations tend to be a bit more fussy and demanding when it comes to environmental conditions. You think you've got it optimized, drives great with perfect low smoke, then the weather changes and all of a sudden it's smokier or laggier.

So again generally speaking, I tend to recommend maf-based tunes for the vast majority of my customers, because it tends to be a better overall experience for all concerned.
 

dieseleux

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MAF do a exact count of air mass to cylinder...
MAP suppose the air mass to cylinder...

With MAP is important to use some IAT map to fuel compensation when temp change.



Dieseleux
 

KERMA

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There's more going on than can be compensated by a just taking pressure, and adjusting density based on IAT.

Remember, pressure is actually RESISTANCE to flow.

If we were discussing a tank of air with a fixed size of open-ended pipe coming out of it, we could definitely calculate mass airflow very accurately based on pressure and temperature in the pipe.

But that's not what we have. VNT is like a reverse throttle on the exhaust. It's effectively a variable throttle valve that creates a variable amount of backpressure on the system, which in turn affects the mass through put.

picture our tank with a pipe, with your temp/press measured in the outlet pipe. Add a throttle valve AFTER the pressure/temperature measuring point. NOW what's the relationship between pressure/temp and mass flow? Not quite as straightforward, is it
 

burpod

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i haven't really noticed any difference with the change of seasons with my maf-less tunes...
 

KERMA

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A VE map.
A VE Map -- Which is made... how? using a MAF maybe?

These cars are developed at the factory with VE empirically measured (with a MAF) on an engine dyno at the T1 supplier or OEM, for ONE *specific* configuration. (IOW stock) In fact, if you know what you are doing, you can even reverse engineer the ECU maps to derive the stock VE.

But... We are hot rodding. Not keeping things stock. This changes VE. Which throws all the density vs pressure assumptions out the window. It gets crazy really quickly. For example.

We add non-stock turbos, injectors, cams, intercoolers, exhausts, delete egr, etc etc etc, and now what is VE? I guess we can assume "it's pretty close still". That may be passable enough for some, but I like to work to a higher standard.

Just consider 1) turbo 2) intercooler 3) exhaust 4) EGR and you are already at 2 x 2 x 2 x 2 = 16 possible combinations if you only have 1 variant each of stock vs those 4 airflow mods in combination. Make it 2 types of turbo mods, vnt17 and 1722, then multiply by 2 again. You are going to measure data and calculate VE maps for all of them? Using what... a maf maybe?

Then VE changes again when you change vnt position and changes with boost pressure, not to mention any throttle on the inlet like the PDs have.

Then there's maps in the ECU that adjust EGR, VNT, Boost, fueling, based on temperatures, and baro. Further confounding things. So, it gets even more complicated in a hurry.

My point is, maybe it's more expedient as hot rodders who care about smoke, for us to measure airflow directly than to suppose or assume based on a single pressure measurement at some random point in this multi-stage system. Cut out the middleman and just measure it directly.

If you don't care about smoke or refinement, just go Mtdi with a wastegate, and call it a day. Just let the LDR diaphragm move a spring-loaded lever on your injection pump in response to manifold pressure, and we are good to go!

Maybe we are better off using the best available tools at our disposal, if we want the best result.
 

loudspl

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i haven't really noticed any difference with the change of seasons with my maf-less tunes...
Try big changes in altitude.
A good example would be tuning for air density changes....such as for cars that run up Pikes Peak...like the old Rally Golf

A MAF tune also works better with headwork. Good porting, big valves, and cam work better with MAF tunes. The MAF sees this and responds with appropriate fuel very quickly

I think this is why some tuners require 3" R32 MAF. It's rated for more flow and doesn't saturate as easily. That same MAF was also used in 444bhp W12 T-Reg if that says anything...:)
 

burpod

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of course, large changes in altitude would make a difference. but this could easily be incorporated into darkscouts thread of a custom ecm - taking into account ambient atm pressure.... but that's a whole different matter. i've taken my cars up into the mountains in NH, and no big deal. of course, we're not talking about some areas out west, but still.

i've also had tunes with the larger maf housing in my mk4s etc..

i am happiest most with the setup i have in my mk1 and mk3. my mk1 has a (locally done) mildly ported head and i couldn't be happier with the setup, except for wishing i had put in rostens in it :(
 

KERMA

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Magnitude matters

A car that makes 105 hp max with VNT17 at 24 psi and stock injectors probably won't be very sensitive to environmental changes, either. In fact, it probably won't smoke no matter what you do.

Now, if you are shooting for 150+ hp with R520 and vnt15 at 18 psi and so forth it will be "somewhat" trickier to stay smoke free all the time in all conditions. There will "probably" be a compromise required, somewhere... now the question becomes, what give your the best result at this extreme.

Most probably fall in a contnuum somewhere in between.
 

KERMA

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hey man that's great, glad to hear it. Good for you.

the OP wanted to know why people were still using MAF-based tunes, and I gave my opinion as to why maf-based tunes were still being used.

Summary: Because it still works, that's why. And... it's there.

Thanks.
 
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burpod

teh stallionz!!1
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hey man that's great, glad to hear it. Good for you.

the OP wanted to know why people were still using MAF-based tunes, and I gave my opinion as to why maf-based tunes were still being used.

Summary: Because it still works, that's why. And... it's there.

Thanks.
ROFL. so that's the secret reason! :D
 

oilhammer

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There are just too many to list....
I think Kerma has made some valid points, and has added a great deal to this thread. Thanks, Kerma.

Also, I'd like to ask: this issue with no MAF input not working well seasonally, is that why I've often had to tweak the IQ winter vs. summer? Seems like my AHU was really sensitive to that type of change. My ALH not so much, but it is there. It is also a pretty mild setup though.
 

darkscout

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A VE Map -- Which is made... how? using a MAF maybe?
Of course. A head of time during calibration/tuning. You tune your VE map during steady state conditions at which point

But... We are hot rodding.
All the more reason to not use a MAF.

Not keeping things stock. This changes VE. Which throws all the density vs pressure assumptions out the window.
Which is why you remap it in a few spots and fill it out.


We add non-stock turbos, injectors, cams, intercoolers, exhausts, delete egr, etc etc etc, and now what is VE? I guess we can assume "it's pretty close still". That may be passable enough for some, but I like to work to a higher standard.
A 'higher standard' that depends on sensor that is far before the intake and possibly ahead of the entire air system?


You are going to measure data and calculate VE maps for all of them?
Why do it for ALL of them? A few hours of data collection and you can be done with it.

Then VE changes again when you change vnt position and changes with boost pressure,

not to mention any throttle on the inlet like the PDs have.
Throttle is used for the low pressure EGR. If you're doing high performance off road tuning you eliminate EGR.

My point is, maybe it's more expedient as hot rodders who care about smoke, for us to measure airflow directly than to suppose or assume based on a single pressure measurement at some random point in this multi-stage system.
You're not measuring airflow directly. You're measuring air flow before the turbo before the intercooler, before all the piping. Pressure and Temperature are measured directly before the intake. Not "some random point". I've been thinking of turning my EGR blockoff plate into a pressure and temperature sensor point.

Cut out the middleman and just measure it directly.
Exactly. Measure the temperature and pressure of the manifold.

Maybe we are better off using the best available tools at our disposal, if we want the best result.
Which is why every diesel manufacturer out there uses MAFs... oh wait. They don't.

Try big changes in altitude.
IMAP needs to be measured in absolute pressure. It's the only way you can properly do the equations.

Summary: Because it still works, that's why. And... it's there.
So does a MAF-less tune. Unless you want to remove it for simplicity.


is that why I've often had to tweak the IQ winter vs. summer?
Sounds more like a fuel temp compensation issue.
 

KERMA

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"Education is Man's going forward from cocksure ignorance to thoughtful uncertainty." -- Kenneth G. Johnson
 

ejg3855

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How about blow thru MAF's they can be placed right before the IM and the pressure will be most accurate as to whats going into the engine.
 

ejg3855

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What was the largest engine you've tuned with no MAF? How many HP did it put out? (ball park).
Dont go down this road, more power doesn't always imply a better tune or more refinement.

I'd be willing to bet that Bosch Engineers that calibrate stock OEM engines have much better tunes/calibrations on them than any aftermarket tuner. Maybe not the most powerful tho.

They have access to way better tools, engine dynos, rolling roads, proper software for real time tuning etc. I have a friend that works for Delphi doing EMS and its just wow compared to what the aftermarket tools are.
 

KERMA

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Dont go down this road, more power doesn't always imply a better tune or more refinement.

I'd be willing to bet that Bosch Engineers that calibrate stock OEM engines have much better tunes/calibrations on them than any aftermarket tuner. Maybe not the most powerful tho.

They have access to way better tools, engine dynos, rolling roads, proper software for real time tuning etc. I have a friend that works for Delphi doing EMS and its just wow compared to what the aftermarket tools are.
Not to mention time, and money

Let's give darkscout's workplace a budget of $350 for a project and see how far they get.

Oh, and you have to do 10 of them today.
 
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