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
I’m going with D if you can’t get the exhaust out then you can pull any air in
Why not B?
D
Restricted Exhaust System. The pressure builds up creating back pressure and reduces air flow causing vacuum to drop. Answers is D
D
I would say that “A restricted exhaust system” is most likely cause of this issue.
Not a mechanical but D Happened to a 73 charger I had. Inner pipe collapsed on the exhaust pipe
I'm going with (A)
Technical Training Development Manager
2moI 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.