mercury

What are the benefits of using a MAF sensor as opposed to a MAP sensor?

rainforest

maf sucks and and map rules. maf you alllways have to mod them. and their allways 2 small. maps the smallest thing you have to do is get a 2 bar or 3 bar map sensor.

mercury

Why do some manufacturers use a MAF then? It doesn't make much sense to me that they'd want to place a restriction in the intake path.

bob01721

Here's the deal. In order to calculate the amount of fuel needed, any fuel injection system needs to know just how much oxygen is entering the engine. Since the oxygen in the air we breathe is (for the most part) constant, we can calculate the amount of O2 by knowing the mass of the air entering the engine. A mass airflow (MAF) sensor measures this.

I'm only aware of two types, but there may be others. The simplest (cheapest) way is to route engine air through a small chamber, making it push past a spring-loaded flap, or door. An electronic sensor then converts the physical position of the door into an electrical signal, which is read by the ECU.

The other type of MAF (mass airflow sensor) is what's known as a "hot-wire" sensor. It takes advantage of the fact that a wire, ANY wire will always have more electrical resistance when it is hot than when it is cool. So, all engine air passes over a thin, bare wire (this is, of course buried within the housing of the MAF). This wire is pre-heated by running electrical current through it. The ECU reads the electrical resistance of this wire to determine the amount of air passing it (the air entering the engine cools the wire somewhat -- more air = cooler wire = lower resistance).

Both MAF systems are VERY susceptable to dirt problems. Spring-loaded flaps can bind. With the hot wire systems, the wire itself accumulates dirt and contaminates from the intake air. This will affect the wire's resistance and the sensor will begin to drift. Also these hot-wires have been known to burn out after a time, and they are pretty expensive to replace.

However Oxygen intake can also be calculated if air density is known. Since we know that air density is affected by atmospheric pressure, the Honda engineers decided it would be better to measure that. So, PGM-FI systems (all the ones I've ever seen) use an atmospheric pressure sensor (MAP) INSTEAD of a mass airflow sensor. Once the ECU knows the atmospheric pressure it can calculate how much air is entering the engine (per crankshaft revolution), and it can meter the fuel precisely. This is a more expensive way to design a fuel injection system because the ECU itself is doing more work (it has to convert atmospheric pressure into air mass values), and because there are more sensors needed overall to make it work this way. However, the precision is better, and the reliability is DEFINITELY better.

I guess that's just a long-winded way of saying, "Manufacturers use MAF because it's cheaper and it's more direct -- less work for the ECU."

RangerGuy

i have maf, and i can say this. if the maf is sized properly, it is somehwat superior to map. somewhat? yep, in the sense that the computer can adjust itself for varying mods. of course there is a limit to what it can adjust for. but take for example simple honda mods. i/h/e. on a map vehicle, a fpr is suggested to adjust, as the computer cannot adjust itself. i say this, thinking i am right..please correct me if i am wrong.

but, a maf vehicle can adjust itself. again the flow restriction. most mafs now are hot-wire mafs. where a heated wire is all that is needed to read the airflow. so much voltage required to heat it and so forth. and again if the maf is sized properly.....no 60mm tb with a 50mm maf.

just my .02

mercury

That's true. On the 240SX, you can boost up to 4psi on the stock engine and fuel system before you max out your stock injectors. Unlike the Honda setup, the ECU doesn't even care if you're boosting!

bob01721

True.

I was talking about MAF vs MAP from a manufacturer's point of view (as in "Why do some manufacturers...?).

My understanding is that, as you said, MAF systems adapt themselves to mods better than MAP systems. They measure air mass directly, whereas MAP systems have to compute it with their firmware.

rainforest

maf's suck on turbos. you need to get the cobra maf by jwt that the poo poo! i cant belive the engineeers at jwt figure that problem out.

EE_Chris

Just to add:

The volume of O2 is also dependent on air temp...so the IAT sensor is also used to calculate how much the engine is taking in.

Also, they include a BARO sensor in the setup to help calculate manifold pressure....remember, its 14.7 psi at sea level...so in high altitude situations, the manifold pressure will be different...so the ECU really takes these two readings and subtracts them to find the true manifold pressure.

You also have to 'know' the V.E. of the engine to make these assumptions...cuz' if its more efficient, its injesting more air....and the V.E. does not stay constant through the rev range, so you can't apply a fixed figure here.

XDEep

found this cuz i was also wondering why manufacturers have been going to MAF's. my mom's 03 highlander (50k) wouldnt start, kept stalling. it would have cost over 500$ for the labor and diagnostic before they would find that it was a dirty MAF sensor. it just so happened that i blew on it while trying to inspect the idle valve and it started. air filter was clean even.

i feel so sorry for all the people who have had to fork out the money for the dealer to replace it, when all that's needed is for it to be cleaned. they probably clean it and stick it in another vehicle..

so chock that up as being one of the idiotic downfalls for MAF sensors - dirt. how come other MAF systems don't have this problem, or as severe? do they design or locate it in a position where it's not as susceptible to dirt?

do any cars still use MAP sensors for their decades of reliable usage?

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mercury &raquo;</TD></TR><TR><TD CLASS="quote">What are the benefits of using a MAF sensor as opposed to a MAP sensor?</TD></TR></TABLE>
MAF systems are more accurate at determining the amount of air entering the engine. Allows for better emmision control.

maxpsi

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Chiovnidca &raquo;</TD></TR><TR><TD CLASS="quote">MAF systems are more accurate at determining the amount of air entering the engine. Allows for better emmision control.</TD></TR></TABLE>

From what I've seen, MAF systems seem to be more responsive to mods. But, alot of the MAF guys I know convert to speed density for less headaches.

Chiovnidca

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by maxpsi &raquo;</TD></TR><TR><TD CLASS="quote">From what I've seen, MAF systems seem to be more responsive to mods. But, alot of the MAF guys I know convert to speed density for less headaches.</TD></TR></TABLE>
Yea, i'm waiting to see what kind of problems the new maf systems are going to have. I have a feeling hondas design will keep problems to a minimum.

maxpsi

The new accords seem to be fine. They've been doing fine on MAF for awhile now. I'm sure it is a similar, if not identical, system to what is on the new Si.

StorminMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by maxpsi &raquo;</TD></TR><TR><TD CLASS="quote">

From what I've seen, MAF systems seem to be more responsive to mods. But, alot of the MAF guys I know convert to speed density for less headaches.</TD></TR></TABLE>

On the other hand, they're restrictive. Therefore, if your mods are extensive, then you need to upgrade the MAF. And if you do this, you are reprogramming the ECU anyway. So this particular advantage to MAF is a little overrated.

I should also mention that MAP allows for simpler and cheaper aftermarket intakes, since there is no need to accommodate a MAF in the intake tubing.

maxpsi

Valid point.