Fuel Injection System Function; Preliminary Checks; Ignition Spark Check - Mercury 150 EFI Service Manual

Wipe up fuel spills immediately.
Depressurize fuel system prior to opening line connections or removing fuel sys-
tem components.
Perform the tests in this section in a well ventilated area to avoid being overcome
by fuel vapors or poisonous exhaust gases.

Fuel Injection System Function

Fuel is delivered directly to the engine by way of fuel injectors. These injectors are provided
with a constant supply of fuel (41 to 45 psi; 283 to 310 kPa) delivered to the fuel rail. The
injectors are opened and closed electronically by the Electronic Control Module (ECM).
The ECM receives input signals from various sensors in the EFI system which in turn trans-
mits controlling outputs (open/close) to the injectors. The length of time the injectors stay
open is considered pulse width. The pulse width will widen (richer) or narrow (leaner) de-
pending on signals ECM receives from sensors, to allow efficient operation at all speeds
and conditions.
IMPORTANT: The following preliminary steps MUST BE FOLLOWED before at-
tempting EFI problem diagnosis.

Preliminary Checks

Ignition Spark Check

Purpose: This test determines if the ignition system is delivering usable spark to the spark plugs. By perform-
ing this test, the probable cause can be isolated to either the ignition system or fuel system.
1. Disconnect all spark plug wires from spark plugs.
2. Connect spark gap tester Quicksilver (91-850439T) to a good ground on engine. Con-
nect Spark Plug Extensions (91-877870A1) between tester and spark plug leads.
3. Connect Remote Starter Switch Quicksilver (91-52024A1) to starter solenoid.
a. Connect RED lead from switch to large positive (+) terminal with RED banded
b. Connect BLACK lead from switch to small terminal with YELLOW/RED lead at-
4. Turn ignition key switch to the "ON" position.
5. Look at spark gap tester viewing port for presence of good quality spark.
A steady, blue spark should be present at each spark plug wire. If a good spark is present,
problem may not be ignition related. If good spark is not present, problem may be ignition
related. Troubleshoot ignition system. Refer to appropriate ignition section in this service
manual.
90-883728 JULY 2001
cable attached [(+) cable from battery].
tached.
OFF
CAUTION
CAUTION
DANGER
ON
START
FUEL INJECTION
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