The Manifold Absolute Pressure (MAP) sensor measures the changes in intake manifold pressure, which result from the engine load and speed changes, and converts this to a voltage output.
A closed throttle on engine coastdown will produce a low MAP output, while a wide-open throttle will produce a high output. This high output is produced because the pressure inside the manifold is the same as outside the manifold, so 100 percent of the outside air pressure is measured.
The MAP sensor reading is the opposite of what you would measure on a vacuum gauge. When manifold pressure is high, vacuum is low. The MAP sensor is also used to measure barometric pressure under certain conditions, which allows the ECM to automatically adjust for different altitudes.
The ECM sends a 5 volt reference signal to the MAP sensor. As the manifold pressure changes, the electrical resistance of the sensor also changes. By monitoring the sensor output voltage, the ECM knows the the manifold pressure. A higher pressure, low vacuum (high voltage) requires more fuel, while a lower pressure, higher vacuum (low voltage) requires less fuel.
The ECM uses the MAP sensor to control fuel delivery and ignition timing.
See Figures 1 and 2
Fig. Fig. 1: MAP sensor terminal identification-except 2.8L, 3.1L and 3.2L engines
Fig. Fig. 2: Terminal identification is stamped on the MAP sensor-except 2.8L, 3.1L and 3.2L engines
See Figure 3
Fig. Fig. 3: Common MAP sensor mounting found on Isuzu trucks
I really believe that this will turn out to be your issue,but other than this i would check out the egr valve,which is Under the hood, center, rear engine area, passenger side of distributor, mounted in block .Thank you.
Sorry to keep bugging you with this Rodeo issue. I have now verified that the EGR is operating correctly and didn't seem to be clogged. I was hoping that it was.I also pulled the MAP sensor tube and noticed that the intake plenum has some black gasy soot in there. I also verified if the ignition system is working and each cyclinder is getting the proper spark.
Here is what I have replaced so far:
Plugs, wires, O2 sensor, air filter, Oil, oil filter, MAP sensor. I have checked the vacuum lines, PVC valve and EGR valve, along with checking for vacuum leaks, none of the hoses seemed clogged
With such a major reduction in MPG (10mpg), I really thought it would be something easy to find.
If you have any other ideas, i would greatly appreciate them.