Engine - Occasional `Jolt' While Driving
84saab01SUBJECT:
INTERMITTENT HOT FUEL DELIVERY M80-83-1/2 900 MODELS
ISSUE: 06/84-691
FILE IN S.I. MANUAL:
VOLUME: I
SECTION: 2
PAGE: 163
Intermittent interruption of fuel delivery during hot ambient conditions has been determined to be caused by deficient Evaporative Control System pressure. If components of this system are not meeting the original specification, or if the fuel filler cap is not properly tightened, the reduction in Evaporative System or tank pressure can cause vapor bubbles to form in the fuel and momentarily interrupt or cause a "miss" in the delivery of fuel from the fuel pump.
The usual symptom of this problem is an occasional jolt which is felt while driving on the highway at steady speed or when depressing the accelerator slightly such as when climbing a grade in hot, humid weather (above 80~F).
NOTE! In order for the instructions of this S.I. to be effective, the car must be in stock condition, i.e., unmodified fuel pick-up trays, tank pressure valve in place and CIS pressures and ignition system within specification.
Details on the repair of this occurance are detailed below:
REPAIR PROCEDURES:
1. Perform a check of the Evaporative Control Pressure system as described in S.I. 05/84-689, Volume I, Sec. 2.
Repair any pressure leakdown faults with the aid of the S.I.
2. Replace the evaporative system pressure valve (P/N 93-0-462 as per the instructions in S.I. 05/84-689 if it does not open and maintain a pressure of at least 1.2 psi (0.08 bar) but not more than 2.2 psi (0.15 bar) for at least 5 seconds.
3. Install a ratcheting-type gas cap (P/N 75-10-530), noting the following:
M80 Models - if not already done, replace filler neck with the appropriate M81-type, P/N 93-35-118. See S.I. 04/81-469, Section 2 from S.I. Supplement No. 2 for details.
M81-83-1/2 Models - if car is fitted with the Saab accessory locking gas cap (also ratcheting-type), replace only if not sealing.
Note that a gas cap of any type will not maintain Evaporative Control Pressure if not properly tightened after a fill-up.
Warranty Information: Total time for verifying tank pressure (Oper. #23400) and changing t e gas cap and pressure valve is 0.8 hour. For M80 models add Operation Number 23431 for 0.5 hour.
The components of the Evaporative Control System should now meet the original specifications of the system. If an intermittent mis or interruption of the fuel system still persists, it will be necessary to make some basic checks of the related electrical and fuel systems of the car that are not affected by Evaporative Control Pressure. See also "Advice To The Owner" block at the end of this S.I.
An intermittent fuel delivery problem should not be confused with an engine miss caused by bad spark plugs, wires, etc.
BASIC SYSTEMS CHECK (Perform if problem persists)
1. Ignition wires. Spark plugs and ignition coil.
^ Check that all ignition electrical connections are clean and tight. Replace any loose or badly corroded terminals.
^ Check the spark plugs for contamination and wear. Check and adjust the spark plug gap if necessary.
^ The spark plug high tension wires must be in good shape. Inspect them for cracked or split wires and any evidence of improper use of spark plug boot pliers.
2. Electrical connections.
^ Check for and correct any loose or corroded terminals at the fuel level sender and fuel pump (see also Recall 257).
^ Inspect the three 29-pin connectors at the fuse box for loose or pushed out connectors.
3. Fuel system (defects can also cause stalling in turns with low fuel levels).
^ The fuel pump height must be correct. Position the pump in the rubber mounting collar so that the distance between the base of the fuel strainer and the upper edge of the rubber mounting collar is 9.29" (236 mm).
Note that the clearance (A) between the upper bracket and the lower bracket is 0.08 - .24" (2-6 mm). The lower bracket was introduced as a running change to reduce pump noise and has no effect on fuel delivery.
^ The pump must be mounted so that + and - terminals are facing the left and right rear wheel respectively.
Also the inlet of the fuel strainer must face to the right side of the car and 45~ to the rear.
The arrow points to the front of the car.
^ A modified fuel pump tray was introduced during late 1982 production. The same tray (P/N 93-62-153) may be installed on cars which may suffer from fuel starvation with low fuel levels. S.I. 06/82-572, S.I. Supplement No. 3, Sec. 2, has details on checking the tray.
^ The fuel pump return line must empty into the fuel pick-up tray. The return line continually fills the tray and must clipped to the tray.
Also the fuel strainer of the fuel pump must sit completely into the tray when installed and the pick-up tray must not be warped or deformed in any way.
The pick-up tray must not be modified with extra holes. The function of the tray is to keep fuel continually feeding the fuel pump with low fuel levels and modifications to the tray defeat this function.
^ Check the CIS line pressure. The checking value for M80-81 models is 4.5 - 5.2 bar at a minimum of 11.5 volts measured at the fuel pump wire connections.
The checking value for M82-83-1/2 models is 4.7 - 5.4 bar, also at a minimum of 11.5 volts measured at the fuel pump wire connections.
NOTE: As from 1983-1/2 models the pressurized fuel tank is changed to a pressurized fuel pump enclosure with a feeder pump. The pressure valve in the vapor line is not used on cars with the feeder pump.
If similar problems occur on the late design, check the function of the feeder pump or a blocked feeder pump pick-up screen.
Advice To The Owner:
- Avoid alcohol enhanced fuel when the ambient temperature exceeds 75~F.
- Always make sure the gas cap is tightened until it ratchets (clicks at least once) whenever fuel has been added.