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Old 01-30-2013, 06:17 PM
oldbogie oldbogie is offline
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Originally Posted by chphlds View Post
hey guys,
trying to figure out why my ecm is for speed density,and I am running maf. no knock sensor installed,but wiring is there.runs rich till warmed up then smooths out,but pings.downloading pics. maybe somebody can see something from these.any input appreciated.
Speed Density and MAF are different air quantity measuring systems, one is not compatible with the other. Speed Density or as it's called Manifold Absolute Pressure (MAP) uses throttle position, manifold vacuum (absolute pressue) and RPM to compute the amount of air being consumed which generates a number that aligns to a look up table that has an amount of fuel with an igniiton timing advance point for that number. Changes to the engine such as a larger cam change the manifold vacuum to the throttle position to the RPMs which really screws with this system.

The Mass Air Flow (MAF) system does not compute the air consumption as MAP does, it measures it using a heated filament that changes temperature in proportion to the air flow over the it. This changes the voltage on the output side of the filament from a known standard voltage being applied to it. This replaces the manifold vacuum part of the sensing used for the MAP system. The output voltage of the MAF sensor doesn't quite track engine power settings the same as from a MAP sensor so the fuel and ignition advance points aren't quite correct if the progammed chip for the type of system (MAF or MAP) is missmatched to the system being used. The MAF system is more flexible when it comes to cam and other changes because anything that changes the air flow past the filament sensor is accomodated, within reason, it doesn't generate incompatible signals to the computer.

Bogie

Last edited by oldbogie; 01-30-2013 at 06:25 PM.
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1Gary (02-24-2013), chphlds (01-31-2013)