Poor fuel mileage can come from a number of component failures. Airmass meter failure, fuel pressure regulator failure or Map sensor failures.
The most common failure on cars with airmass meters would be a thinning platinum wire on the airmass meter. When this occurs the air mass flowing across the wire cannot be calculated correctly causing more fuel to be used due to correct readings.
When fuel pressure regulators fail the diaphram in the regulator typically breaks causing fuel to be pulled into the vacuum hose, into the intake and out the exhaust without the fuel being burned. When this happens the fuel pressure regulation is skewed causing excess fuel consumption.
MAP stands for Manifold Absolute Pressure Sensor. It is basically a sensor that monitors engine vacuum. When this component fails the readings to the Electronic Control Module are skewed causing the injector mixtures to be incorrect causing poor fuel mileage.
Another often overlooked poor fuel mileage issue is the failure of a Ignition component such as a DI Cassette or a Ignition cartridge on a V6 car. When one of these fail you may blame the fuel system but the problem could be ignition. Most of the time when an ignition component fails you will know it because of a dead engine miss. On the V6 it is more difficult to spot because you have 6 cylinders to drop verses 4 cylinders. The 4 cylinder cars are much more evident because of less cylinders to fail which means that power will more diminished.
Pricing for AIR MASS METER (electrical components)
Pricing for AIR MASS METER (fuel system & related)
Pricing for ENGINE SENSORS (engine parts external)
Pricing for ENGINE SENSORS (engine parts internal)
Pricing for ENGINE SENSORS (fuel system & related)
Pricing for ENGINE SENSORS (heating & cooling system)
Pricing for FUEL PRESSURE REGULATORS (fuel system & related)