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09-15-2004, 07:28 PM
#1
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Car: 84 berlinetta
Engine: 305
Transmission: auto
What's This?
passenger side rear of the engine between the engine and a/c - heater box. there is a blue plug with 3 connectors (sort of looks like the one that goes into the tpi on a ccc). it is not connected to any thing and i can't see any thing to hook it up to. the egr solenoid is 2 wire and that's the closest thing i see. wish i had a dig cam to show you all. any help appreciated.
09-16-2004, 03:31 PM
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Car: 4
Engine: 6
Transmission: 5
No, not the MAP sensor; baro sensor. Similar but different.
The MAP sensor is over between the brake booster and the fender.
MAP is useless (or at least, not fully precise) as a measure of "vacuum", without also knowing the ambient barometric pressure. "Vacuum", which is the indicator of engine load, is the difference between ambient and MAP. They added that sensor to provide more accurate fuel metering by a more accurate measurement of vacuum.
The MAP sensor is over between the brake booster and the fender.
MAP is useless (or at least, not fully precise) as a measure of "vacuum", without also knowing the ambient barometric pressure. "Vacuum", which is the indicator of engine load, is the difference between ambient and MAP. They added that sensor to provide more accurate fuel metering by a more accurate measurement of vacuum.
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09-16-2004, 04:45 PM
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Car: 1989 Iroc-Z
Engine: 350ci SBC
Transmission: 700R4
I stand corrected...thanks RB...you are a wealth on knowlege...How then are the 90-92 cars running with no baro???
09-17-2004, 02:22 AM
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Car: 92 Form, 91 Z28, 89 GTA, 86 Z28
Engine: 5.7 TPI, LG4
Transmission: 700R4, 700R4
Axle/Gears: 3.27, 2.73
Slow, MAP based speed density systems are MAP which stands for Manifold Absolute Pressure. Absolute means they can tell the pressure with respect to a complete vacuum without a reference Baro pressure sensor. LG4s had a vacuum sensor which isn't referenced to a complete vacuum. They needed a Baro sensor to be able to get the load calculation right (they could have used a MAP sensor, but they probably hadn't either figured it out yet, or didn't have the processing power to do it all with respect to cost).
The speed density EFI cars use the MAP sensor reading at key on, engine not running as BARO. They also update the baro reading at high throttle positions. Speed density EFI systems aren't particularly sensitive to baro though. Mainly Baro is used on those systems to get the cranking fuel and IAC right. The only other main effect is that it reduces exhaust back pressure at high altitude, which changes the volumetric efficiency slightly.
I think the main reason for MAP and Baro on an LG4 is ignition timing. The fueling is coarse with the CCC. Even then, the stock LG4 timing table is laughable, especially at WOT. There has been some work done recently to hack the ECU, so if the correct equipment is bought, it can be changed!
The speed density EFI cars use the MAP sensor reading at key on, engine not running as BARO. They also update the baro reading at high throttle positions. Speed density EFI systems aren't particularly sensitive to baro though. Mainly Baro is used on those systems to get the cranking fuel and IAC right. The only other main effect is that it reduces exhaust back pressure at high altitude, which changes the volumetric efficiency slightly.
I think the main reason for MAP and Baro on an LG4 is ignition timing. The fueling is coarse with the CCC. Even then, the stock LG4 timing table is laughable, especially at WOT. There has been some work done recently to hack the ECU, so if the correct equipment is bought, it can be changed!