Troubleshooting - Fuel System

Introduction

This troubleshooting guide is intended to help identify and repair fuel system problems. Symptoms covered:

• Excessive Fuel Consumption
• Strong Fuel Smell In Passenger's Compartment

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Excessive Fuel Consumption

Possible Cause	Checks	Refer To
Dirty Air Filter	Check and change the air filter.	N/A
Bad O₂ Sensor (if equipped)	Check the sensor and replace if necessary.	FUEL-18
Poor Ignition System Function	Check the condition of the distributor cap and rotor. Check the condition of the spark plugs and spark plug wires.	IGN-04

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Strong Fuel Smell In Passenger's Compartment

A raw fuel smell inside the cabin almost always traces back to one of three areas: the seal where the fuel level sender enters the tank, the fuel tank ventilation (evaporative) system, or the fuel filler and reservoir system in the rear of the car.

Possible Cause	Checks	Refer To
Fuel Level Sender Seal	Inspect the seal where the sender enters the tank — see Fuel level sender seal.	ELECT-13
Fuel Tank Ventilation System	Inspect the evaporative hoses and the charcoal canister — see Fuel tank ventilation system.	N/A
Fuel Filler or Fuel Reservoir System Leak	Inspect the filler and reservoir hoses, valves, cap, and neck — see Fuel filler and reservoir system.	N/A

Fuel level sender seal

Using ELECT-13, locate the fuel level sender and check the condition of the seal around the sender cap.

On 1985.5 and newer cars the sender seals with a gasket. If the gasket appears hard or brittle, remove the sender and replace it. The part number for the sealing ring is 944 201 327 00.

Early cars are less prone to this problem because they use an O-ring between the sender and the top of the tank, with the sender held by five cheesehead screws each carrying its own seal ring. Fuel smell on an early cars can come from any of these seals failing. The sender O-ring is part number 477 919 133, and the seal rings for the cheesehead screws are part number M 013 802 1.

Fuel tank ventilation system

The fuel tank has a ventilation system designed to prevent pressure buildup in the tank by carrying off fuel vapor. Hoses run from the tank along the bottom of the car on the right-hand side, into the engine compartment, along the back of the firewall, to a charcoal canister in the left fender well. Remove the interior fender well cover to reach the canister.

Any of those fuel lines that is loose, cut, or leaking will produce a strong fuel smell inside the passenger compartment. A charcoal canister that is split or otherwise leaking will do the same.

Fuel filler and reservoir system

A number of rubber hoses and sleeves in the fuel filler and reservoir system can cause a fuel smell if they develop holes or if their hose clamps come loose. These components sit in the rear hatch area — behind the carpet on the fuel filler side of the car, and behind the panel on the inside of the roof pillar on that same side.

Stuck ventilation valve. When a fuel system ventilation valve sticks, fuel vapor can leak into the cabin. A noticeable "whooshing" sound when you remove the fuel filler cap is a good sign that a valve is stuck. The early fuel system uses two valves: a shut-off valve and a ventilation valve. The shut-off valve is part number 928 201 083 02; the ventilation valve is part number 810 201 186 A. The late fuel system uses only the shut-off valve (928 201 083 02).

Leaking fuel cap gasket. A worn fuel cap gasket lets fumes past the cap. The late-car gasket is part number 944 201 553 00; early cars used part number 477 201 553 (most likely the same part under an earlier number).

Elongated fuel filler neck. Over time, repeated fueling lets the weight of the fuel nozzle distort the filler neck, so the cap no longer seals and fumes reach the cabin. The neck is a replaceable sleeve. Early cars with chassis code up to 94EN4 00060 use part number 931 201 281 01; all other 944s use part number 931 201 281 02.