Pontiac FIREBIRD 1972 Service Manual page 1122

8-2 1972 PONTIAC SERVICE MANUAL
I
F U E L GAUGE CHECKING PROCEDURE
DASH UNlT READS FULL
WlTH IGNITION SWITCH ON
1. DISCONNECT TANK UNlT FEED WlRE AT
TANK UNIT.
2. WlTH VOLTMETER CHECK FEED WlRE VOLTAGE.
SHOULD READ APPROX. 9 VOLTS. WlTH LOW
FUEL WARNING 5-6 VOLTS.
N O VOLTAGE READING
CHECK FOR PROPER CONNECTIONS AT:
1. DASH UNlT CONNECTOR AT GAUGE.
2. BODY HARNESS CONNECTOR TO CHASSIS
HARNESS CONNECTOR.
3. BODY HARNESS CONNECTOR AT BACK OF
REAR SEAT CUSHION.
CORRECT VOLTAGE READING
1. CHECK GROUND WlRE FROM TANK TO TRUNK
FLOOR PAN FOR CONTINUITY.
2. CONNECT SPARE TANK UNIT. RAISE AND LOWER
FLOAT ARM OBSERVING DASH UNIT. IF DASH
UNIT'FOLLOWS ARM MOVEMENT, REPLACE TANK
UNIT.
1
DASH UNlT READS EMPTY
I
WITH IGNITION SWITCH O N
DISCONNECT TANK UNIT. DASH UNlT SHOULD N O W
READ FULL.
I
I I
GAUGE READS FULL
1. CONNECT SPARE TANK UNIT.
2. RAISE AND LOWER FLOAT ARM WHILE OBSERVING
I I
DASH UNIT. IF DASH UNlT FOLLOWS ARM
MOVEMENT, REPLACE TANK UNIT.
I
U
GAUGE READS EMPTY
1. CONNECT SPARE DASH UNIT. IF FULL READING
SHOWN. DASH UNIT SHORTED. REPLACE.
'
I
2. IF STILL READS EMPTY, SHORT I N HARNESS
BETWEEN TANK UNlT AND DASH UNIT.
I
I
DASH UNIT NEVER READS FULL
1
-
7
, , A
ERRATIC FUEL GAUGE READINGS
I
1. FUEL TANK MUST B E FILLED TO CAPACITY.
2. NOTE DASH UNlT NEEDLE POSITION WlTH
ENGINE RUNNING.
3. DISCONNECT FEED WlRE TO TANK UNIT.
4. WlTH OHMMETER CHECK RESISTANCE OF TANK
UNIT. SHOULD READ APPROXIMATELY 88.0-93.0
OHMS WlTH FULL FUEL TANK.
NOTE: GAUGE FLUCTUATION DURING
ACCELERATION OR DECELERATION IS
NORMAL.
CHECK THE FOLLOWING:
1. DASH UNlT MOUNTING SCREWS.
2. DASH UNlT CONNECTOR.
3. BODY HARNESS CONNECTOR TO
CHASSIS HARNESS.
4. GROUND CONNECTION FROM TANK UNlT
TO TRUNK FLOOR PAN.
5. FEED WIRE CONNECTION AT TANK UNIT.
LOW RESISTANCE READING
1. FLOAT ARM BENT.
2. TANK MOUNTlNG AREA DEFORMED.
NORMAL RESISTANCE READING
REPLACE DASH UNIT.
I
I
I
I
MANY FUEL GAUGE TANK UNITS ARE REPLACED BECAUSE OF POOR
DIAGNOSIS OR LACK OF KNOWLEDGE OF THE VARIABLES I N THE SYSTEM.
FOR EXAMPLE:
TYPICAL COMPLAINT-THE GAS GAUGE READS EMPTY AND ALL THAT
WAS REQUIRED TO FILL THE TANK WAS 19 GALLONS.
REASON: 1 . EMPTY FUEL RESERVE (1-2 GAL.)
2. HIGH VOLUME PUMP; STATION ATTENDANT DID NOT TAKE
TIME TO TOP-OFF TANK AFTER PUMP "SHUT OFF" THE
FIRST TIME. LOSS OF .5 TO 1.5 GAL.
3. POSITION I N WHICH CAR WAS FILLED. IF CAR IS
EXCESSIVELY LOW O N EITHER SIDE, THIS MAY CAUSE AIR
TO B E TRAPPED I N THE TANK THAT CANNOT BE VENTED,
PREVENTING COMPLETE FILLING OF THE T A W .
I
Fig. 8-1 Fuel Gage Checking Procedure