Question

all of the following conditions lead to a black colored exhaust except

a. a leaking or sticking fuel injector.
b. a leaky vacuum diaphragm on the fuel pressure regulator.
c. an open coolant temperature sensor circuit.
d. a blown head gasket.

Explanation:

• A leaking or sticking fuel injector (a) can cause an overly rich fuel mixture, leading to black exhaust.
• A leaky vacuum diaphragm on the fuel pressure regulator (b) can increase fuel pressure, resulting in a rich mixture and black exhaust.
• An open coolant temperature sensor circuit (c) can make the engine computer think the engine is cold, enriching the fuel mixture and causing black exhaust.
• A blown head gasket (d) typically causes white or grayish - blue exhaust (due to coolant or oil entering the combustion chamber), not black exhaust.

Answer:

d. A blown head gasket.