Dissolve

If they are running MAFs, how do they sense boost from the factory? Do they have a MAP sensor as well as their MAF? Or do they have some sort of boost sensor in the intake manifold connected directly to the ECU???

Dan W

Speed-Density uses a pressure sensor (MAP - manifold air pressure) and does a somewhat complex calculation with engine size and RPM injector size and the fuel tables to estimate the amount of air entering the engine and the fuel to go with it.

MAF's (mass air flow) by contrast measures airflow directly... pressure doesnt even come into the calculation for fueling.

Dissolve

Right, but how do factory supercharged/turbo cars sense boost? There are some turbo cars, for example, that come with MAF. These cars have to have another way to measure boost since their MAF cant do it. They must have a boost sensor or something similar in the intake manifold. Correct?

rhuarc31

I hate it when people post yet don't answer the question.

The answer is that most factory boosted FI systems (not gonna say all because i haven't looked at all the systems out there) use a MAP sensor to detect boost. In a standard FI system the MAP is usually a 1 bar type. In boosted application they step up to a 2 or 3 bar MAP that then reports the intake pressure to the computer and the computer enriches the mixture accordingly. BTW a boost sensor that reporst boost to the ecu is a MAP sensor. Some systems use both a maf and a map. And obviously you can add a supercharger to a maf car, but the computer will not be able to effectively boost reference the fuel hence the need for things like FMU's which up fuel pressure to artifically add more fuel without using the computer. People also use things like an extra injector hooked to a hobbs switch or alcohol/propane injection to provide enrichment without the computer.

ATOMonkey

When I was calibrating, there was a sensor for everything. We used MAF to calculate fuel and EGR flow rates, as well as MAP and EGP to determine EGR driving pressure. Then you did a seperate calibration to determine how pulse width affected fuel delivery based on pressure, temperature, and MAP. Then you get to determine timing based on all of those inputs, plus manifold temp and pressure, oil temp, etc. At the same time, you're calibrating PID controllers to get the proper engine response while walking the fine tradeoff line of NOx and HC/particulates. Newer engines also have instantaneous crank speed calculators that trim individual injectors to even out firing pressure. Just be glad you don't have hydraulically assisted injectors in gas engines. All electronically actuated TB engines use that to drive EGR as well as a host of other things, which adds another layer of complexity.

All engine conrtol strategies are different, which makes it really hard to make blanket statements as to how engines operate. Plus most of that is extremely hard to get your hands on unless you work on the inside. I guess the moral of my story is that it's fairly easy to get a good enough calibration worked out on your Z, but damn near impossible to do a really good one, unless you start from scratch.

Guido

Wow ATO that was a really good description!

dissolve, I still dont know why you are fishing aruond for information on your car, on this board. There arent many people here who are qualified to give you an accurate answer.

StumpPuller

the DSMs (Eclipse, Talon, Laser) were MAF, and were turbo.

The stock boost gauge "estimated" (I'm serious) boost. It wasn't a "real" boost gauge.

So you pretty much have to tap the manifold to wire up a real one.

Damon

How about we ask some real-world situational questions. Like what did the following cars use:

1. Grand National. (MAF + 2 bar MAP?)
2. Turbo Sunbird (mid 80s). (speed density with 2 bar MAP?)
3. Eaton-Supercharged 3800 in GM intermediates in recent years (dunno)

I think I know, but I don't know that I know.

B4Ctom1

the sc3800's use the maf and 2 bar as well

aftermarket EFI centrifugal supercharger kits as well as a few roots/screw types use a FMU which is an assisting fuel pressure regulator that cut the return line and cranks up pressure to the injectors. Although it is not exact it is fairly sufficient and is used on thousands and thousands of cars with aftermarket blowers on the road with great success.

for more discriminating hot rodders aftermarket ECM's are the rage, the best employ a combination of a 2 bar map sensor to sense the boost and wide band O2 to correct for any occurance outside the scope of the user created programming. these are offered by a few companies including Accel (gen 7) and F.A.S.T.

Grumpy

A MAF sensor can't tell boost from boots.
Given a table that looks at gm/sec vs RPM the ecm could be made to understand the different VEs, from N/A to boosted.

A MAF sensor, actually the ecm has to do math to calculate air flow. It's just a different sensor to develope a load calculation. One of the problems with MAFs is that they read air flow, but in either direction, so reversion can complicate it's calibration.

rhuarc31

Wow, look at the smart people come out fo the woodwork That was a nice post ATO. DIssolve, check out www.twinturbo.com they may be able to give you a better answer, or www.z32.com, or there are a bunch of z car related sites that may have more specific info for you. I came across a bunch of them looking for info on my new '84 Z project car.

CrazyHawaiian

I've been confused about this in the past (click here to read about my confusion lol). This is how I understand it (please correct me if I'm wrong). The MAF sensor measures air. The MAP sensor measures pressure. Both work with the cars ECM to calculate how much fuel to deliver. The MAF works in real time making calculations on the fly depending on what the MAF sensor reports. The MAP is pre-programmed meaning if it encounters X ammount of pressure, apply X ammount of fuel (pressure should dictate the ammount of air being delivered). Speed Density setups use a MAP sensor instead of a MAF sensor, thus they are referred to as a MAP system. MAF setups of course use the MAF sensor to reach the same goal, but at the same time they can also use a MAP sensor to account for boost if the ECM is designed to work with the MAP sensor.

N/A motors using MAP run a 1 bar MAP sensor. This will read from -30 (vaccum) to 0 psi or regular atmospheric pressure. Then you have a 2 bar map which will read from -30 vaccum to 14.5 psi (1 bar boost). Then you have the 3 bar MAP sensor that will read from -30 vaccum to 22.something psi (2 bar boost). Either intake setup (MAF or SD) can have either a 1, 2, or 3 bar MAP sensor, but if the MAF setup is N/A then a MAP sensor is not needed.

So to answer your question, if the car was running MAF and had a 2 bar MAP sensor, then the ECM would be able to account for boost up to 14.5 psi. If the same MAF car was N/A, it would probably not have a MAP sensor meaning no boost, just vaccum. And it would make sense because the ECM would not need any input as far as pressure because the MAF sensor is feeding it air data. So for a car to be able to work with boost from the factory, the car will need to have a 2 bar MAP sensor (or bigger) from the factory.

askulte

Think of it in the big picture. Your engine need X amount of fuel molecules for Y amount of air molecules. The MAF measures the amount of air flowing past, and tells the ECM that you are using Y air, so inject X fuel. The MAP sensor does the same thing, indirectly. It measures the pressure inside the plenum. Air moves from high pressure (plenum) to low pressure (cylinder chamber), so the larger the pressure in the plenum, the more air molecules will get into the cylinder. There is a table, based on RPM and Manifold Pressure (MAP) that has injector pulsewidths (i.e. add X amount of fuel for Y amount of air). Whether you run NA (0 to 1 bar of manifold pressure), low boost (0 to 2 bars of pressure), or higher boost (0 to 3 bars of pressure), the engine doesn't care. All it ultimately needs to know for steady state is the amount of air going into the cylinders, which can be either MAP, MAF, or both... It might help to think in terms of absolute pressure (from a total vaccuum, 0 psi) to ambient (Naturally aspirated at WOT = 14.3 (or 14.7?) psi absolute, is 1 bar), and over 1 bar for pressures above atmospheric (i.e. boost). Or did this help confuse things even more?

Andris

83 Crossfire TA

iTrader: (2)

It doesn’t make a difference if you use MAF or MAP to figure it out. MAF will measure the mass of the actual airflow and it doesn’t make a difference what the boost or air density is, MAP measures the pressure and then the ecm basically uses a chart to approximate airflow and determine fueling. You don’t need to know the boost at all, just how much air you’re getting so you can mix it with the proper amount of fuel.

I don’t know about the older GM setups, but most current GM PCM’s have both, whether it’s boosted or not. They use the MAF to determine air flow, and the MAP sensor to determine how other things are working (for example, on OBDII cars, GM PCMs (and I’m assuming most others) check for a pressure change when the egr is opened to make sure that it’s not plugged or disconnected).

BTW, there are plenty of boosted cars, OEM and otherwise running just a MAF