Concerns

Generally, fuel system concerns can be divided into two categories:

1. Vehicle will not run.
2. Vehicle runs but lacks power or exhibits poor driveability.

Causes of a will-not-run condition include:

^ Obstructed, pinched or kinked fuel supply system lines and/or filters
^ Electrical system malfunction
^ Inoperative electric fuel pump

Causes of a lack of power or poor driveability include:

^ Restricted fuel supply system plumbing
^ Resistance causing excessive voltage drop in fuel pump electrical circuit
^ Sluggish electric fuel pump output
^ Contaminated or substandard quality fuel

Gasohol and Alcohol/Gasoline Blends

Gasohol, a mixture of gasoline and ethanol (grain alcohol), is available in some areas. Gasohol, if used, should contain not more than 10% ethanol and have an octane rating of 87 or higher.

In some cases, methanol (wood alcohol) or other alcohols are added to gasoline or to Gasohol. Such additions may be noted on the pump, or the the station attendant may be aware of them. In certain concentrations or formulations, these additives may cause driveability problems and may be injurious to fuel system materials.
Fuel System Plumbing Concerns

^ Restricted fuel pump inlet filter
^ The inlet filter may become restricted and/or deteriorated due to contaminate in the fuel tank.
^ The inlet filter may be pushed up against the pump inlet by a deformed fuel tank.

A restricted fuel pump inlet filter can be detected by checking fuel flow at the fuel supply hose near the tank with the fuel pump energized. (See Fuel System Volume Check later in this article.)

In one instance, it was reported that a fibrous material that was dispersed in the fuel tank progressively collected on the pump inlet filter and caused the vehicle to lose power after an extended period of operation. When the vehicle was shut down for a short time, the material re-dispersed and allowed the vehicle to operate normally for another extended period. In this case normal diagnostic procedures did not reveal the cause of power loss. Removal of the fuel tank was required to remove the fibrous material.

In another instance it was reported that the fuel pump inlet filter was deteriorated and material lodged in the fuel pump rendering it inoperative. It was suspected that methanol (wood alcohol) in the fuel was the cause.
^ Obstructed and/or kinked fuel supply line
^ There are three sections of the fuel supply line that are composition hose and are subject to kinking.
^ The metal and composition fuel lines are subject to obstruction by foreign material or separated hose lining.

Obstructed fuel supply lines may be diagnosed by visual examination and checking fuel flow at various locations in the supply line. Fuel system lines should be cleaned in any situation where fuel contamination has been found to cause obstruction of the vapor separator inlet screen and/or the carburetor inlet filter.

^ Obstructed or inoperative fuel tank selector valve (dual tank equipped with vehicles).
^ The selector valve can be a receptacle for foreign material that will restrict fuel flow from one or both fuel tanks.
^ The selector valve may fail to operate, which will not allow fuel delivery from one of the tanks.

Diagnosis of restricted fuel selector valves may be accomplished by fuel flow checks downstream of the valve. Diagnosis of an inoperative fuel selector valve is described in TSB 83-22-21.
^ Fuel is removed from one tank and delivered to the other tank (dual tank equipped vehicles).
^ Internal leakage in the fuel tank selector valve may allow fuel to flow from one tank to the other.

NOTE: This condition was encountered on some fuel tank selector valves that were provided in early service kits that converted a fuel system from mechanical engine mounted fuel pump to electric fuel pumps in the fuel tanks. The service kits were recalled in Recall 452 during the 1982 calendar year. No fuel tank selector valves of this type have been installed in production vehicles nor are they any longer included in fuel pump conversion service kits.

^ Obstructed vapor separator.
^ The screen at the inlet part of the vapor separator may become obstructed with foreign material.
^ The spring loaded valve at the outlet end of the vapor separator may become obstructed.

Diagnosis of the separator valve may be done by checking fuel flow at outlet of valve after establishing adequate flow at the inlet end. The valve may also be checked off the vehicle by visual examination of the inlet screen and blowing through the valve with a finger held over the return port. Remember it takes 1 PSI to unseat the spring loaded valve, so you will have to blow hard.

NOTE: In the event the inlet screen is obstructed, the valve can often be made serviceable by cleaning in solvent. A backflushing of the inlet screen is recommended.

^ Obstructed carburetor inlet filter.

The carburetor inlet filter is quite small and of a very fine micron rating. It is not always possible to determine by visual examination if the filter is obstructed. Generally, if there has been contamination detected in the fuel supply system, the carburetor inlet filter should be replaced.

Fuel System Electrical Concerns

An understanding of the electrical circuits will enable a technician to select diagnostic steps to determine where malfunctions are occurring. However, the following items have been reported:

^ Corrosion in the fuel pump cut off relay and/or the fuel tank selector relay.

In the event moisture enters the relay from road
splash or wet environmental conditions the relay will malfunction due to corrosion of the contact points.

^ Inertia switch opens under impact.

FIGURE 16:

^ The inertia switch requires manual resetting after it has been opened by impact. A facsimile of the instructions in the vehicle owners guide is reproduced in Figure 16.
Fuel System Volume Check

^ Separate the fuel supply line at the vapor separator inlet. Connect a rubber tube to the supply line and route it into a gallon measure container.

FIGURE 17:

^ Remove the connector from the fuel pump cut off relay. Connect a jumper lead to the terminals marked A and B in Figure 17 to energize the electric fuel pump.
^ When fuel flow has been established, measure the quantity of fuel delivered during a period of fifteen seconds.

NOTE: The fuel system must be capable of delivering a minimum of one quart in fifteen seconds.

^ In the event the fuel flow is less than specified, it must be determined if the shortage is due to fuel system restrictions or an electrical malfunction.

^ If the fuel flow meets specifications and the vehicle will not run or lacks power due to a lack of fuel, the vapor separator valve, the carburetor inlet filter and/or internal carburetor conditions are the likely causes.

NOTE: On vehicles equipped with dual fuel tanks, the volume check must be performed on both tanks. The IGNITION SWITCH must be in the RUN position and the FUEL TANK SELECTOR SWITCH in the position of the tank to be checked.