MAF-less tunes

[darkscout]

Can anyone explain to me why most people still use MAF tunes?

MAF is really only useful as a diagnostic and tuning tool (at least where I've used it). I know most large engines don't use MAF, it's just a cheap and easy way to diagnose if your EGR is working. (Speed Density-EGR = MAF). Plus it's a bit laggy.

Is there a reason most tuners still use the MAF?

 

[GTiTDi]

I don't miss my MAF, or my N75 valve for that matter

 

[burpod]

i don't miss mine either, but am also confused why many tuners still use the maf...

 

[oilhammer]

Because many areas have OBD/emissions tests, and that is how you check for EGR functionality.

I have a MAF-delete tune of unknown original on my ALH, however, and it has the EGR readiness set but I am not sure if it clears and resets instantly (I assume it does) but even that may not work soon for OBD tests.

 

[IndigoBlueWagon]

MAF provides precise measurement of air flow, allowing the tune to meter fuel and boost to match air flow and request. Although maf-delete tunes can work well (I drove my Golf for a summer with one, including a bunch of track days) the car will smoke more in some situations and FE won't be as good as a MAF included tune. Whether or not you use a MAF in earlier cars is less impotant, as both the MAF and programming is less sophisticated. And if your MAF tune is laggy that's a tune problem, not a MAF problem. MAF tunes for my cars, please.

 

[drewkeen]

MAF provides precise measurement of air flow, allowing the tune to meter fuel and boost to match air flow and request. Although maf-delete tunes can work well (I drove my Golf for a summer with one, including a bunch of track days) the car will smoke more in some situations and FE won't be as good as a MAF included tune. Whether or not you use a MAF in earlier cars is less impotant, as both the MAF and programming is less sophisticated. And if your MAF tune is laggy that's a tune problem, not a MAF problem. MAF tunes for my cars, please.

Well put

 

[nexus665]

Absolutely agree with IBW - actually, it's the other way around.

Boost measurements are taken about every 20ms, MAF is taken every ms - so that's a factor of 20:1 in favor of the MAF...laggy tune is just that - a laggy tune.

Regards

 

[darkscout]

MAF provides precise measurement of air flow

Which is great at steady state conditions. But unless you're running a genset, you'll almost never have that other than at say cruise control.

It's a great device for tuning your engine and calculating volumetric efficiency but once you get those maps correctly setup.

smoke more in some situations and FE won't be as good as a MAF included tune.

Then the maps were setup wrong. I still have yet to get on an engine with a MAF and our customers care a lot more about FE than VW's. There are other limiting maps, however I'm not sure if VW's software structure is setup for them.

The MAF will always be 'ahead' of the MAP meaning you're going to over fuel on acceleration going up the curve. A pressure and temp sensor as close to your intake manifold with a well calibrated VE map and it's going to be much better.

And if your MAF tune is laggy that's a tune problem, not a MAF problem. MAF tunes for my cars, please.

My MAF tune isn't laggy. The MAF itself is laggy. It's the fundamental of how the MAF works and the momentum of the air system. The bigger your plenum mass (FMIC, bigger turbo, longer piping) the more off the MAF will be.


The reason I asked is I know a lot of people are running a MAF tune and I plan on eliminating mine for tuning purposes (will probably keep it as a calibration device). I wasn't sure if there was a good reason most people kept theirs other than 'that's what VW did.

 

[darkscout]

Boost measurements are taken about every 20ms, MAF is taken every ms - so that's a factor of 20:1 in favor of the MAF...laggy tune is just that - a laggy tune.

That means absolutely nothing. That's not a factor of 20:1 in favor of everything. How many times do you check your mail per day? Well I check mine 500 times a day. That's a factor of 500:1 that my postman is better than yours. It makes absolutely no sense.

Have you calculated how far air travels in 1 ms? The physical response of the engine can't be an order of magnitude faster than 20 ms anyway. That's a boost reading 50 times a second and I know most turbos don't spool that fast. They probably sample it that fast because of how inaccurate it is so they can toss a low pass filter on it anyway.

Also, for my application boost sample time doesn't matter. I plan on having a faster sensor anyway.

 

[ejg3855]

MAF provides precise measurement of air flow, allowing the tune to meter fuel and boost to match air flow and request. Although maf-delete tunes can work well (I drove my Golf for a summer with one, including a bunch of track days) the car will smoke more in some situations and FE won't be as good as a MAF included tune. Whether or not you use a MAF in earlier cars is less impotant, as both the MAF and programming is less sophisticated. And if your MAF tune is laggy that's a tune problem, not a MAF problem. MAF tunes for my cars, please.

In the diesel world if engine speed is controlled by fuel flow and thus we always assume maximum airflow is always available to the engine what does the MAF do? As long as the ECU "maps" know what the VE's and the MAP Sensor readings of the engine are I'd say MAF readings are pointless. Maybe I am off balance here, Your statement I 100% agree with in the gas world where we control engines from an airflow standpoint.

 

[nexus665]

Have it any way you like it darkscout - the docs say different

As an aside - have you ever directly measured boost with a pressure sensor? You'll see what I mean in regards to stable and "quick" - depending on how fast you measure. There is "some" filtering involved...boost is in no way linear, it is pulsed. The MAF already does all its corrections and sends a fast PWM signal, which the ECU reads. It does not filter it, but it does some sanity checking and adds correction factors - all way faster than even getting two readings that need to be filtered further.

Regards

 

[ejg3855]

Which is great at steady state conditions. But unless you're running a genset, you'll almost never have that other than at say cruise control.

I have no idea about newer Diesel ECU's but i know in the gas ME7.5 ecu there are calibrations for volumes/speeds/time/volume over throttle plate to know all these air flows of the specific motors (gas). Its quite a powerful ecu if you read over the eleventybillion page functional document.

 

[vanbcguy]

With regards to the MAF itself though - it's a heated wire, you are measuring a resistance change based on a temperature change. From that alone we know there is lag. Next you have the entire intake tract to deal with while the MAF is at the air box. Actual airflow in to the engine is changing quite a bit faster than the MAF could ever actually react to based on its position and the technology involved.

Fortunately it doesn't really matter - diesel engines just aren't that picky about ratios. MAP + IAT tells you most of what you need to know. As long as you stay on the right side of the AFR curve to keep smoke limited you are fine regardless of what measurement inputs you use.

 

[IndigoBlueWagon]

I feel like we're feeding a troll. I have no objection to MAF delete tunes. I just prefer to use the mechanism that VW engineers (who I venture know a lot more about this than any of us here) feel is a benefit to making their engines run at their best.

If you don't like them, don't write them. Most owners won't understand or recognize the difference anyway.

 

[nexus665]

The point is, the MAF does this continuously all on its own and outputs a high-speed digital signal as opposed to having a significant reading every combustion cycle.

It is definitely quicker - and MAP+IAT does NOT tell all you need to know. You should factor in EMP, as well.

You can have high boost pressure but still move no air mass - and have no power, all because of EMP spikes, which hinder the exhaust gasses from exiting the cylinders. A MAF is a good tool to have even if you run MAF-less (MAP-based smoke limiting) just to do some sanity checking.

I also have no problem with MAF-less tunes.

Regards

 

[darkscout]

Have it any way you like it darkscout - the docs say different

What 'docs'? I have my own set of 'docs' and experience.

As an aside - have you ever directly measured boost with a pressure sensor? You'll see what I mean in regards to stable and "quick" - depending on how fast you measure.

Does 50kHz sound like enough sampling? Yes I know what a boost sensor looks like. I've run plenty of FFTs on them and EGR and every other sensor on our engines.

It does not filter it, but it does some sanity checking and adds correction factors - all way faster than even getting two readings that need to be filtered further.

The signal is filtered. Be it in software or hardware. No one uses a raw signal. (I'd hope not). And if it's such a 'perfect' sensor why does it need correction factors?

Its quite a powerful ecu

Powerful engine means nothing without the software spec. It could be a very powerful controller but

 

[nexus665]

So, then you know how often you can measure relevant boost pressure - it ain't 50KHz

900/min = 15 rps
4500/min = 75 rps

Again, how often do you gain useful measurements at 50, 100, 10 million KHz?

Still, I'll leave you to your own devices. I'm talking about the Bosch docs regarding MAP and MAF sensors - but then, you already knew that.

Regards

 

[darkscout]

I feel like we're feeding a troll.

What was the last engine controller you worked on?

I just prefer to use the mechanism that VW engineers (who I venture know a lot more about this than any of us here) feel is a benefit to making their engines run at their best.

VW engineers that had to live with EGR. IF you are trying to diagnose a failed EGR than a MAF is an awesome tool. It's unreliable (relatively speaking) and the primary reason a lot of diesel manufacturers don't use them.

The point is, the MAF does this continuously all on its own and outputs a high-speed digital signal as opposed to having a significant reading every combustion cycle.

Except it is fundamentally flawed as it is it is not what is going into the cylinders.

and MAP+IAT does NOT tell all you need to know.

Yeah, yeah it does. Well that plus Volumetric Efficiency. Once it's mapped for a Turbo it's fixed. So unless you're swapping turbos every other day, you are able to get away with a fixed VE map.

 

[darkscout]

So, then you know how often you can measure relevant boost pressure - it ain't 50KHz

4500/min = 37.5 cycles/s

Again, how often do you gain useful measurements at 50, 100, 10 million KHz?

I'll have to check the FFT but you get a pulse per cycle. To satisfy Nyquist you need to sample at ~>2 fastest frequency. Meaning you can probably get away with 50 Hz just fine. I'm sure if there was a significant contribution or resonance VW would have sampled faster.

 

[JFettig]

so I have not read most of the posts in this thread but here are my 2 cents.

If the MAP limiter is set up correctly, it will NOT smoke more, and you will NOT get worse fuel economy. That said no tuner will take that much time to do it. I set up mine based on AFR and it works beautifully.

The one and only reason I'd like to have a MAF in my car is for low load conditions where the turbo is closing off the vanes to build boost - exhaust is so restricted that I can make, for example 15psi but its not flowing jack compared to vanes open at 10psi. In order to make it smoke free with just a MAP limiter, it needs to be smoke free with the vanes shut, thus not having linear power to boost to AFR, which isn't a big deal IMO.

 

[Gearhead51]

I have a MAP tune that makes great power when the MAF is disconnected, but makes bad smoke pulling away from the light. When I plug the MAF back in, some of my power at low TPS is gone, as is my smoke. It's nice and clean easing away from a light. Honestly, that's what I want, but I lose a third of my top end when it's plugged in, too.
I don't mind smoke when it's GO TIME, but I hate the puffs when easing away from a light. I'd like a tune that looks at MAF at low load, but ignores it past 80% tps. I'm no tuner, so I don't know if it's possible.

And why is my CEL always showing a MAF code when unplugged??? Can that be written out? I'm about to jump on ecu connections and do some reading.

 

[JFettig]

You don't have a MAP tune, you just have a tune that gives full fueling when your MAF is unplugged.

A tune can get optimized to the point where you have the best of both worlds without the smoke(with MAP or MAF tuning), but like I said above, no tuner will want to spend that much time on a car, especially without dyno tuning it, in person.

 

[Gearhead51]

I must have misunderstood what I was getting, then. My tuner is pretty far away. I guess it really is time to get studied up on tunes.

I do have a Alientech Powergate V1. The sticker on the back says "ogni configurazione difforme dall'originale deve essere utilizzata solo per la circolazione in circuito chiuso" translated "configuration different from each should be used only for circulation in a closed circuit"

 

[dieseleux]

For MAF-less tune, O2 wide band is great tools!
On stock engine, VW have right quantity of fuel (fuel pump voltage map) and air (MAF) go in engine and do a right mix to make right combustion.
On modify engine, lot of owner throw away MAF and dont have any information feedback of air/fuel, some time is too rich, some time is lean and no smoke, some time at lot rpm engine smoke like a train... is not a tune, is juste like old TD engine, a few turn on fuel screw!!!
Is possible to do a good MAP tune with right tools and time, because many tdi setup are custom and need a custom tune.




Dieseleux

 

[Bob_Fout]

As I understand, in Europe, MAF input is ONLY used for EGR calculations, nothing to do with fuel amounts? Can anyone confirm this?

 

[GTiTDi]

As I understand, in Europe, MAF input is ONLY used for EGR calculations, nothing to do with fuel amounts? Can anyone confirm this?

Yes I would think so...from the early info I have read on the system it was only needed to measure flow during EGR operation....

 

[Seatman]

If my boost is increased my fueling also goes up, how does it do this if not by using the maf? Does the maf not measure air flow as in what the turbo is sucking through the pipe? And does the ecu not then use that info to deal with fuel flow?

Just asking.

I have a maf but no egr and zero lag. I would say that the egr can cause lag rather than the maf, mine was doing that, a strange sort of hesitation but as soon as I disconnected the egr it went.

 

[vwmikel]

As I understand, in Europe, MAF input is ONLY used for EGR calculations, nothing to do with fuel amounts? Can anyone confirm this?

Some, but not all European TDI's use the MAP sensor for smoke limitation. And, as some have hinted at, there are two kinds of "MAF Delete" tunes out there. Some simply reset the default value for when it throws a MAF error (such as when it's unplugged). This will cause excessive smoke as there is little linear progression to the fuel delivery. A proper MAF delete tune allows fueling to rise in a linear fashion based on boost pressure.

 

[ejg3855]

If my boost is increased my fueling also goes up, how does it do this if not by using the maf? Does the maf not measure air flow as in what the turbo is sucking through the pipe? And does the ecu not then use that info to deal with fuel flow?

.

MAP plus IAT allows you to calculate the density of the charge, which gives you the volume that the ecu looks to a calibration for in its tables for proper fueling.

Search and read about speed density tuning.

 

[oilhammer]

I have a couple observations, and this includes gasoline-fueled cars as well. If a MAF is totally not necessary, then why do so many (the vast majority) of automakers use them? 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.

Now, the OP says none of the other diesel engine makers use them, but that is not true. Every single one of the road-going diesel engines under 10k GVWR use a MAF sensor. Volkswagen, Ford, BMW, Mercedes-Benz, GM, all of them. And with the exception of Ford using Siemens, everyone uses Bosch EDC. Could this be a conspiracy for Bosch to sell more MAFs?

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. And they probably don't have any engines that are asked to go from 900 RPMs to 4000+ RPMs within a second while still meeting those same emissions requirements.

So to that end, it would seem a MAF is a very integral part of an EPA-compliant emissions friendly engine management system. Also, all of the new diesels I am talking about have throttles. All of them. On a Sprinter, if the MAF wigs out, the ECU cannot operate the throttle and EGR valves, and it reverts to dumbassed mode, running wide-open throttle, closed EGR, and reduced power.

So that gets us back to the original question of "why do tuners use the MAF?" Well, if it is already present, and you are wanting to keep the engine at least close to emissions compliance, then why not? I don't see how you could accurately operate these systems without one. But if you don't care about that, OR are wanting to build an EDC system from scratch like in the other thread, and perhaps using said home-built EDC system in a swap or some other more unregulated diesel engine, then the simplicity of a MAFless setup has its merits. Especially if you can do it without any adverse driveability or ill effects like smoking, lagging, etc. Simple is always good. If I put a TDI engine in my Vanagon, you can bet it won't have any extra bits it does not absolutely NEED to make the engine operate in a reasonable manner. Heck, even a 75hp SDI engine would be a substantial upgrade .

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.

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.