ENGINE PERFORMANCE SOS/ASE QUESTIONS AND ANSWERS WITH SOLUTIONS 2024 What are the key components in an EVAP system? - ANSWER Fuel Tank, gas cap, lines/hoses, and charcoal canister Catalytic Converter: - ANSWER Oxidizes NOx into CO and HC When testing a connector what is an acceptable reading? a.) 1V from ground side b.) 1V from positive/reference side c.) .5V from at each connector d.) 1.5v from sensor harness - ANSWER C An oxygen sensor is reading 400mv, what would this indicate - ANSWER lean condition What increases NOx emissions? - ANSWER High combustion temperatures You have examined a set of spark plugs and found them to have a black crusty finish on them. What does this indicate? - ANSWER Rich air/fuel mixture A vehicle comes in with poor performance, low power and a flashing check engine light. What would this indicate? - ANSWER Engine misfire What is the function of the EGR valve? - ANSWER to recirculate exhaust gases into the intake Emission control systems are installed on engines to reduce what 3 specific exhaust emissions? - ANSWER (HC) hydrocarbons, (CO) Carbon Monoxide, and Oxides of Nitrogen (NOx) You are monitoring the TPS/APP sensor voltage reading with slow steady acceleration should read: - ANSWER .50v at idle to 4.5 at WOT If the voltage reading on one cylinder is not high enough, what is the most likely source of the problem? - ANSWER Bad spark plug At WOT the PCM module reverts to: - ANSWER Open loop, rich mixture What are the 2 types of EVAP Leaks? - ANSWER 0.020 small leak and 0.040 large leak 1.) All the following are pre -combustion emission controls except: a.) Catalytic converter b.) PCV system c.) Timing control systems d.) EGR systems - ANSWER A Tech A says that HCs result from unburned fuel and from incomplete combustion. Tech B says that CO is formed with a mixture that is too rich. Which Technician is correct? - ANSWER Both Port injection injects fuel: - ANSWER Injects fuel behind the intake valve (DI) Direct Injection: - ANSWER Injects fuel directly into the combustion chamber (Diesels) What do post -combustion control systems do? - ANSWER Cleans up exhaust gases after fuel has been burnt What does the downstream O2 sensor do? - ANSWER monitors catalytic converter efficiency Why is idle speed increased during a cold start? a.) To prevent misfires b.) To warm up the catalyst c.) To make it easier to drive away d.) To heat up the hot wire in the MAF sensor - ANSWER A Which of the following does the PCM use to determine air flow? a.) BARO b.) ECT c.) MAF d.) HO2S - ANSWER C What does the PCM do to ignition timing during WOT? a.) Advance b.) Retard c.) Overlap d.) Set to base - ANSWER A In a DTC code what does "U" signify? - ANSWER Communication code (Network) OBD II monitors have specific criteria that must be met in order for them to run and complete. What are they called? a.) Type A faults b.) Drive cycles c.) Emissions standards d.) Enabling conditions - ANSWER D When is freeze frame data stored? a.) When a DTC is set b.) When the vehicle was last shut down
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