Q: Vehicle starts sometimes, but dies and won't restart.

asked by on December 13, 2016

Have Code 33 about MAP sensor but vehicle will not run. Changed fuel filter but EFI is not spraying gas. Checked all hoses and connections. Vehicle sometimes starts but only runs a few minutes and dies.
My car has an automatic transmission.

To clarify, the year (1978) of the Chevy Suburban in question you are asking about refers to some EFI terms that a vehicle of this year would not have otherwise come with from the factory. The answer below assumes this is correct and this Suburban has a later model EFI motor in it.

The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance. When the computer reads a heavy load signal from the MAP sensor, it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation (spark knock) that can damage the engine and decrease performance. This may also be caused by other closely related components such as a dirty or failing mass air-flow sensor, a faulty throttle position sensor or potentially a vacuum leak. It sounds like you may have a faulty MAP sensor causing inefficient or abnormal fuel injector spray, which would explain the starting and dying symptoms you describe. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your MAP sensor.

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