Snap-On Diagnostics DGA 1000, Руководство пользователя

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Vehicle Testing Procedures
No-Start Condition—Fuel Test
A vehicle that cranks over but does not start, could be
experiencing:
•
Mechanical engine problem,
•
Ignition system problem, or
•
Fuel delivery problem.
Use the following test to help determine if the fuel supply system is
the problem.
Testing Tip
X
If the TPS fails in a way that mimics a wide-open throttle, even
though the throttle is closed, fuel delivery will be severely
limited or shut off completely due to the clear-flood function
built into the engine control computer. In this event, this test
will indicate a fuel delivery problem even though no other
components may have failed. Always check TPS voltage on
engines with electronic fuel injection if the engine turns over
but will not start. Certain engine mechanical problems,
particularly those relating to valve timing, can prevent the
movement of fuel through the combustion chamber even if the
fuel system is otherwise working properly. In these cases,
valve timing problems may be noticed when the engine turns
over. A change in normal engine cranking rhythm could
indicate valve timing problems.
Test
1. Insert the sample probe into the vehicle tail pipe.
2. Crank the engine for 15 seconds.
3. If no CO value is displayed, partially block induction
system air intake and check for vacuum while cranking the
engine.
✓
On vehicles with electronic fuel injection, check:
— Electronic control module fuse,
— Fuel injector fuse,
— Fuel pump relay/inertia switch, and
— Throttle position sensor (TPS).
Interpretation
•
When the engine gets fuel while cranking, the HC reading
increases,
— This indicates fuel system operation from the fuel tank,
through the engine and out the exhaust.
•
Poor vacuum with some HC reading could indicate a fuel system
problem in carbureted engines.
After troubleshooting systems with catalytic converters for no-start
conditions, allow time for the fuel to evaporate from the converter
before starting the engine. Starting the engine with a catalytic
converter loaded with an excessive amount of unburned fuel vapor
can damage the converter.