Pontiac Fiero 1988 Service Manual page 644

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (PORT) 6E3-B-5
DETONATION /SPARK KNOCK
Definition: A mild to severe ping, usually worse under
acceleration. The engine makes sharp metallic knocks that
change with throttle opening. Sounds like popcorn popping.
• Check for obvious overheating problems:
Low coolant.
Loose water pump belt.
Restricted air flow to radiator, or
restricted water flow thru radiator.
Inoperative electric cooling fan circuit.
> CHECK:
Ignition timing. See Vehicle Emission
Control Information label.
Exhaust gas recirculation (EGR) system
for not opening - CHART C-7.
Transmission/transaxle converter clutch
(TCC) operation - CHART C-8.
Fuel system pressure. See CHART A-7.
Programmable read only memory (PROM) -
Be sure it's the correct one. (See Service
Bulletins)
Valve Oil seals for leaking.
• Check for incorrect basic engine parts such as
cam, heads, pistons, etc.
• Check for poor fuel quality.
• Remove carbon with top engine cleaner. Follow
instructions on can.
CUTS OUT, MISSES
Definition: Steady pulsation or jerking that follows engine
speed, usually more pronounced as engine load increases. The
exhaust has a steady spitting sound at idle or low speed.
• Perform careful visual check as described at
start of Section "B".
® Check for misfiring cylinder by:
1. Disconnect idle air control (IAC) motor.
Start engine. Remove one spark plug wire
at a time using insulated pliers.
2. If there is an RPM drop on all cylinders
(equal to within 50 rpm), go to ROUGH,
UNSTABLE, OR INCORRECT IDLE,
STALLING symptom. Reconnect IAC
motor.
3. If there is no RPM drop on one or more
cylinders, or excessive variation in drop,
check for spark on the suspected
cylinder(s) with J 26792 (ST-125) Spark
Gap Tool or equivalent. If no spark, see
Section "6D" for Intermittent Operation or
Miss. If there is spark, remove spark
plug(s) in these cylinders and check for:
Cracks
Wear
Improper Gap
Burned Electrodes
Heavy Deposits
• Perform compression check on questionable
cylinder(s) found above. If compression is low,
repair as necessary. See Section "6".
• Disconnect all injector harness connectors.
Connect J-34730-2 Injector Test Light or
equivalent 6 volt test light between the harness
terms, of each injector connector and note light
while cranking. If test light fails to blink at any
connector, it is a faulty injector drive circuit
harness, connector, or terminal.
• Perform the Injector Balance Test. See CHART
C-2A.
• CHECK:
Spark plug wires by connecting ohmmeter to
ends of each wire in question. If meter reads
over 30,000 ohms, replace wire(s).
Visually inspect distributor cap and rotor for
moisture, dust, cracks, burns, etc. Spray cap
and plug wires with fine water mist to check
for shorts.
Fuel System - Plugged fuel filter, water, low
pressure. See CHART A-7.
Valve timing.
Secondary voltage using a shop ocilliscope or
a spark tester J-26792 (ST-125) or
equivalent.
• Remove rocker covers. Check for bent pushrods,
worn rocker arms, broken valve springs, worn
camshaft lobes. Repair as necessary. See Section
PF
6A".