Engine Performance & Diagnostics Flashcards

Fuel pressure is within specification at idle but drops well below specification under wide-open throttle on a road test. What is the most likely cause?

Answer: Weak fuel pump or restricted filter

A pump or supply restriction may keep up at low demand but cannot deliver enough volume under high load.

Fuel pressure bleeds down quickly after engine shutdown, and the engine has a long crank on restart. Which is a possible cause?

Answer: Faulty fuel pump check valve

A leaking check valve lets fuel drain back to the tank, so the pump must rebuild pressure before startup.

On a returnless fuel system, where is the fuel pressure regulator usually located?

Answer: In the fuel tank pump module

Returnless systems put the regulator in the tank module, so no return line to the tank is needed.

A gasoline direct injection engine sets a low rail pressure code. Which component is most often responsible for generating high rail pressure?

Answer: Camshaft-driven high-pressure pump

GDI engines use a mechanical high-pressure pump, usually driven by a camshaft lobe, to reach rail pressures above 2,000 psi.

An injector balance test shows one injector with a much smaller pressure drop than the others. What does this indicate?

Answer: Injector is restricted or clogged

A smaller pressure drop means less fuel flowed through the injector during the pulse, which indicates a restriction.

A current ramp captured with a low-amp probe on a fuel injector shows no 'pintle hump.' What does this most likely mean?

Answer: The pintle may be stuck or not moving

The hump is caused by pintle movement, so its absence suggests the pintle is not opening.

Which EVAP condition is most likely to cause a rich condition and rough idle right after refueling?

Answer: Purge solenoid stuck open

A purge valve stuck open draws heavy fuel vapor from the freshly loaded canister into the intake at idle.