Pontiac Fiero 1988 Service Manual page 514

DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI) 6E2-B-5
P O O R F U E L E C O N O M Y
Definition:
Fuel economy, as measured by an actual road test, is
noticeably lower than expected. Also, economy is noticeably lower than it
was on this car at one time, as previously shown by an actual road test.
CHECK:
Engine thermostat for faulty part (always open)
or for wrong heat range. See Section "6B".
Fuel Pressure. See CHART A-7.
Check owner's driving habits.
Is A/C "ON" full time (Defroster mode "ON")?
Are tires at correct pressure?
Are excessively heavy loads being carried?
Is acceleration too much, too often?
Suggest driver read "Important Facts on Fuel
Economy" in Owner's Manual.
Perform "Diagnostic Circuit Check."
Check air cleaner element (filter) for dirt or
being plugged.
Check for proper calibration of speedometer.
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Visually (physically) Check:
Vacuum hoses for splits, k i n k s and proper
connections as shown on V e h i c l e E m i s s i o n
Control Information label.
Ignition wires for cracking, hardness and proper
connections.
Remove spark plugs. Check for cracks, wear,
improper gap, burned electrodes or heavy
deposits, repair or replace as necessary.
Check compression. See Section "6A".
Check TCC for proper operation. See CHART C-8.
Use "Scan" tool if available.
Check for dragging brakes.
Check for exhaust system restriction. See
CHART " B - 1 "
Suggest owner fill fuel tank and recheck fuel
economy.
ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING
Definition:
The engine runs unevenly at idle. If bad enough, the car may
shake. Also, the idle may vary in RPM (called "hunting"). Either condition
may be severe enough to cause stalling. Engine idles at incorrect speed.
• CHECK:
- Vacuum hoses for splits, kinks and proper
connections as shown on Vehicle Emission
Control Information label.
- P/N switch circuit. See CHART C-1A.
- For injector leaking. Check Fuel Pressure
CHART A-7.
- IAC - See Code 35.
- If a sticking throttle shaft or binding linkage
causes a high TPS V o l t a g e (open throttle
indication) the ECM will not control idle.
Monitor TPS voltage. "Scan" and/or Voltmeter
should read less than 1.2 volts with throttle
closed.
- EGR "ON" while idling will cause roughness,
stalling and hard starting. CHART C-7.
- Battery cables and ground straps should be clean
and secure. Erratic voltage will cause IAC to
change its position resulting in poor idle quality.
- IAC valve will not move if system voltage is
below 9 or greater than 17.8 volts.
- Power Steering - CHART C-1E. ECM should
compensate for Power Steering loads. Loss of this
signal would be most noticable when parking and
steering loads are high.
MAP Sensor - Ignition on engine stopped.
Compare MAP voltage with known good vehicle.
Voltage should be the same ± 400 mv (.4 volts).
OR
Start and idle engine. Disconnect MAP sensor
electrical connector. If idle improves substitute a
known good sensor and recheck.
A/C compressor or relay. If inoperative, refer to
CHART C-10.
A/C Refrigerant Pressure too high. Check for
overcharge or faulty pressure switch.
Cooling fan inoperative - See CHART C-12.
PCV valve for proper operation by placing finger
over inlet hole in valve end several times. Valve
should snap back. If not, replace valve.
Run a cylinder compression check See Section
Inspect oxygen sensor for silicon contamination
from fuel, or use of improper RTV sealant. The
sensor will have a white, powdery coating, and
will result in a high but false signal voltage (rich
exhaust indication). The ECM will then reduce
the amount of fuel delivered to the engine,
causing a severe driveability problem.