ASE - National Institute for Automotive Service Excellence’s Post

A box truck equipped with a gasoline engine will not exceed 50 mph. A vacuum gauge is connected to the engine and a steady reading is observed at idle. When the rpm is raised to 2000 and held there, the vacuum gauge reading drops and stays low. No DTC’s are found during a diagnostic check. Which of these could be the cause? A: An intake system leak B: Worn camshaft lobes C: A restricted fuel filter D: A restricted exhaust system

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Aaron Golas

Technical Training Development Manager

2mo

I would like to see you add gauge readings or further elaborate on "reading drops" to eliminate any confusion. When looking at a vacuum gauge most have a positive and negative reading, with zero being the resting point. When looking at vacuum you should obviously have a negative reading at idle and it should go closer to zero when opening the throttle. So are you saying the reading is going more negative when you say lower or are you saying lower indicates going toward zero which would be less negative? Also a "steady reading" doesn't mean it was a good reading at idle. This would be a good question to depict a gauge with actual readings.

Joe hopson

CTE teacher WSFCS Adjunct instructor at GTCC

2mo

I’m going with D if you can’t get the exhaust out then you can pull any air in

Federico Ortiz

Experienced Sales Manager | Automotive Parts, Presentations

3mo

Why not B?

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Drew Anderson

Vehicle Services Training Manager at Cox Automotive, Inc.

3mo

D

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Jeffery Lewis

Transportation Director / Automotive Repair Expert, Master Jaguar/Land Rover and Ford Technician

2mo

Restricted Exhaust System. The pressure builds up creating back pressure and reduces air flow causing vacuum to drop. Answers is D

Dr. John Kershaw

President at Criterion Technical Ed Consultants, Inc

2mo

D

I would say that “A restricted exhaust system” is most likely cause of this issue.

Merrit Baker

Retained Search/Talent Acquisition / Recruiter/ Entrepreneur / Business Consultant. Please No Cypto, Bitcoin etc.

3mo

Not a mechanical but D Happened to a 73 charger I had. Inner pipe collapsed on the exhaust pipe

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