i just had a weird question and figured it would make for some good chatting. obd 1 isnt a self learing system but ob2 is. so whats the point of swaping a speed density car to mass air if its still obd 1? any ideas?
OBD1 comes in Speed Density and Mass Air Flow versions. It differs from OBDII in that diagnostic data cannot be streamed through the diagnostic port in a real time mode. The diagnostic data is stored in volatile memory and dumped on command by an external jumper or code reader connected to the computer’s diagnostic port. Watching the Check Engine Light, an external test light or voltmeter are all that is need to dump the codes on an OBDI system. An OBDI code reader can be used, but it isn’t an absolute necessity.
ODBII is capable of streaming data through the diagnostic port in real time mode. It requires a code reader that handles the OBDII data format. No code reader, no way of knowing what the codes are. The plus is you can watch changes in sensor data as they happen, and use the information to plan changes in the computer's program. OBDI requires a laptop & some specialized hardware to do the same thing.
Both OBDI & OBDII have adaptive learning to accommodate changes in sensor output, so as the sensors and airflow values change, the computer adjusts for them. Mass Air systems have a greater range of adaptive learning than Speed Density.
Speed Density uses Manifold vacuum (MAP), Throttle position (TPS) and RPM, Air Temperature (ACT) & Engine Coolant (ECT) to guess how much air the engine is pulling in. Then it uses all of them to calculate the air/fuel mixture. It is dependent on steady manifold vacuum and minimal changes in airflow from the stock engine configuration to maintain the proper air/fuel ratio. Change the airflow or vacuum too much and the computer can't compensate for the changes, and does not run well. Forget about putting a supercharger, turbocharger or monster stroker crank in a Speed Density engine, because the stock computer tune won’t handle it. Every time you seriously change the airflow through the engine, you need a new custom burned chip to make the engine run at peak performance.
Mass Air uses a Mass Air Flow meter (MAF) to actually measure how much air is being pulled in and uses the inputs from the TPS, ACT, ECT, RPM and Barometric Pressure sensor (Baro) to calculate the proper air/fuel ratio. It is very tolerant of changes in airflow, and vacuum and tolerates wild cams, high flowing heads, and changes in displacement with minimal difficulties. Larger injectors can be used with an aftermarket calibrated MAF or a custom dyno tune. This makes it possible to use the stock computer with engine displacements from 302-408 cu in, and make many modifications without a custom dyno tune chip. Put a new intake manifold on your 331 stroker and the computer figures out how much more fuel to deliver without having to have a new chip burned to accommodate the extra airflow.
The way I figured it out, I needed it put simply:
SD basically manages your engine with a 'chart'.
It looks at all the inputs from your sensors, and then compares them to a built in chart to tell it how much fuel you need.
MAF manages your engine in real terms.
It looks at how much air is coming in, and uses that real data to determine how much fuel you need.
One is relatively unbending and somewhat blind to what is really going on, the other is flexible.
Of course this is oversimplified, but that's what some people like me need to figure it out.