MAP based fuel metering...don't understand fully

Eunos_Cosmo

Eunos_Cosmo

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If anybody on here is really good with tuning EFI systems on cars, maybe they can explain this to me. I know that a MAF sensor can measure air mass fairly directly, but some tuners eliminate the sensor completely and just rely on the MAP sensor to calculate the air mass. It's been a while since I took chemistry, but I don't understand how a manifold absolute pressure sensor, alone, can calculate air mass precisely and reliably. An in-depth explanation would be appreciated, as I can seem to find anything that goes beyond the basics.
 
16.1 is wayy lean. A naturally aspirated engine makes best power right at stoich. Turbo cars need to stay under 12 to prevent pre-igntion. So I'm guessing the manifold absolute pressure/temp gives you the mass of the incoming air? The thing that is confusing me is the load and rpm dependent aspect of it.
 
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Using a bit of math known about how the world works, combined with a load sensor (the map sensor), throttle position readings and rpms they can get an accurate account of how much air is going through the engine.

The math is reliant on the engine being left alone, IIRC Ford's MAF system on 80's mustangs is very adaptable to massive amounts of changes because it can account for changes in pressure and mass air flow from the sensors, map based cars need the ecu recalibrated.

There is a user on this forum that is an ECU tuner, he had a thread titles "automotive molester" or something along those lines, shoot him a PM.
 
thedguy said:
Using a bit of math known about how the world works, combined with a load sensor (the map sensor), throttle position readings and rpms they can get an accurate account of how much air is going through the engine.

The math is reliant on the engine being left alone, IIRC Ford's MAF system on 80's mustangs is very adaptable to massive amounts of changes because it can account for changes in pressure and mass air flow from the sensors, map based cars need the ecu recalibrated.

There is a user on this forum that is an ECU tuner, he had a thread titles "automotive molester" or something along those lines, shoot him a PM.
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Are you referring to Ford's earlier speed density systems? Because I know those would run lean with even the slightest mods. And thanks I'll shoot him a pm.

Seems like some people run map based tunes on their original MAF cars, and I can't understand why really. MAF works well up to well over 1000hp and its very adaptive to changing variables. If you eliminate the extra intake plumbing, maybe you would get slightly better throttle response, but I can't see many advantages. Do you need this type of metering for cars equipped with individual throttle bodies?
 
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starfox07 said:
Are you referring to Ford's earlier speed density systems? Because I know those would run lean with even the slightest mods. And thanks I'll shoot him a pm.
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I'm honestly not sure which one I'm speaking of. I think it's the late 80's, early 90's EFI mustangs. I don't really follow fords but I think the system was called EEC-IV or some crap like that. All I can remember was a magazine talking about a factory Ford EFI system that when reset and allowed to re-learn could adapt to a massive number of changes, assuming the engine didn't blow up before it could adapt ;)


Seems like some people run map based tunes on their original MAF cars, and I can't understand why really. MAF works well up to well over 1000hp and its very adaptive to changing variables. If you eliminate the extra intake plumbing, maybe you would get slightly better throttle response, but I can't see many advantages. Do you need this type of metering for cars equipped with individual throttle bodies?
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I haven't seen any aftermarket/custom ITB setups run MAF, all use map sensors. Interestingly enough though pretty much every factory setup running ITB use a MAF, BMW's and Skyline GT-R's come to mind. Though I believe Toyota's 4age used MAP only on some years and a combo of both on others.
 
starfox07 said:
Are you referring to Ford's earlier speed density systems? Because I know those would run lean with even the slightest mods. And thanks I'll shoot him a pm.

Seems like some people run map based tunes on their original MAF cars, and I can't understand why really. MAF works well up to well over 1000hp and its very adaptive to changing variables. If you eliminate the extra intake plumbing, maybe you would get slightly better throttle response, but I can't see many advantages. Do you need this type of metering for cars equipped with individual throttle bodies?
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This is from my conversations with some tuning buddies of mine. Basically according to them MAP is better if you are running a turbo setup. Since it is not reliant on measuring incoming air you can have a diverter valve that vents into the atmosphere and not end up running rich.

They also mentioned that MAP's are more accurate when it comes to deciding the AFR for the engine in any given conditions.

I don't understand exactly how or why just telling you what I know :)
 
thedguy said:
I haven't seen any aftermarket/custom ITB setups run MAF, all use map sensors. Interestingly enough though pretty much every factory setup running ITB use a MAF, BMW's and Skyline GT-R's come to mind. Though I believe Toyota's 4age used MAP only on some years and a combo of both on others.
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Most custom ITD setup have velocity stacks and no airbox, whereas most production setups (M3 engine for instance) has a large airbox that feeds from one primary intake tube where the filter and MAF is located, from what I've seen. I guess with map tuning, you do everything you want to do, then tune it one time, and don't change anything, otherwise it will throw the calculations off.
 
Funny that we were discussing the Ford EFI system earlier, as I just got my latest hot rod issue and they were talking about it.

The system is Ford's EEC-Iv on the 5.0 mustangs. Basically the computer can automatically adapt to larger injectors, upgraded MAF sensors, etc, and be run on any engine you want that still uses pistons.
 
thedguy said:
Funny that we were discussing the Ford EFI system earlier, as I just got my latest hot rod issue and they were talking about it.

The system is Ford's EEC-Iv on the 5.0 mustangs. Basically the computer can automatically adapt to larger injectors, upgraded MAF sensors, etc, and be run on any engine you want that still uses pistons.
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Is the EEC-IV speed density or is it Mass Air? Because I know the speed density is about opposite of what you just said.
 
EEC-IV could be programmed to do either. Most often, it was MAF, though.
 
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