If your A8 or S8 D2 smells of fuel, the cap is almost certainly the problem
Owners of the 1997–2003 Audi A8 (D2) and its V8-powered sibling, the S8, share one frustrating problem that almost every car develops sooner or later: a faint, persistent smell of petrol — sometimes only after a long drive, sometimes constantly. By the time the smell becomes obvious, there is usually a small but growing pool of fuel under the rear of the car after refuelling.
Nine times out of ten, the cause is the same. The top cap of the in-tank fuel pump assembly has cracked.
This is not a rare failure mode. It is a known weakness of the D2 platform, well documented across A8 owner forums, and it affects A8 2.8, A8 3.7, A8 4.2 and S8 cars alike — because they all share the same in-tank pump architecture.
Why the original Audi cap cracks
The original fuel pump cap on the D2 was injection-moulded from a plastic that was never engineered for 25–30 years of constant fuel exposure, heat cycles, and vibration. Over time, the plastic becomes brittle. The clamping forces from the locking ring, combined with vibration and ethanol-blended fuel attacking the polymer, cause stress cracks to develop around the cap's neck and around the fitting outlets.
Once a crack forms, three things start to happen:
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Fuel vapours escape into the cabin and around the rear of the car
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Liquid fuel begins to weep, especially after refuelling to a full tank
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The fuel system loses pressure containment, which can affect cold starts and hot restarts
Dealers and many independent garages historically told owners that the fuel pump assembly could not be repaired — that the only option was a full assembly replacement, and in some cases that the tank itself needed to come out for inspection. That advice was, to put it kindly, overcautious. The pump assembly absolutely can be repaired, and the cap is the part that needs replacing.
Don't be tempted by a 3D-printed cap
In recent years, a small market has sprung up on auction sites for 3D-printed replacement caps. We strongly recommend avoiding them. Here's why:
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3D-printed plastics are porous. Fuel can wick through layer lines over time, causing the same leak problem you're trying to solve.
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FDM-printed parts have weak interlayer adhesion. The cap is a clamped, vibrating part — exactly the kind of load 3D prints fail under.
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Most 3D-printed caps use PETG or ABS, neither of which has the long-term ethanol resistance of factory-grade polymer.
A properly engineered replacement should be precision injection-moulded, ideally from a glass-fibre-reinforced material that is stronger than the original — not a 3D-printed approximation.
What part numbers does this affect?
The original Audi D2 fuel pump cap is referenced under two OEM numbers, depending on production date and supplier:
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4D0298087B
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D24D0298133C
If you check the top of your in-tank assembly and read either of these numbers (or no number at all, on later production), you have the affected unit.
The proper fix: a full repair kit, not just a cap
When the cap cracks, the rubber seals, hoses, and fittings around it have also lived a hard life. Replacing the cap in isolation and reusing 25-year-old rubber is a false economy — you'll be back in the tank within 12 months.
The correct repair uses a complete kit:
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A new top cap (ideally glass-fibre reinforced)
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A new top rubber seal — the one that sits between the cap and the tank flange
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New fuel-resistant hoses
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New clamps
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New fittings
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Refreshed wiring
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A new molded lower metal/rubber gasket
Our Audi D2 A8 / S8 Fuel Pump Repair Kit was developed specifically to solve this problem. The cap is injection-moulded — never 3D-printed — and reinforced with glass fibre, making it dramatically more resistant to cracking than the original Audi part. Every kit ships with every seal, hose, clamp, fitting and gasket needed to bring the assembly back to a factory-tight condition, and each unit is tested over thousands of real-world miles before release.
How to install the kit (overview)
This job is well within the ability of a competent DIY mechanic. Plan for 2–4 hours, depending on how cooperative your fuel lines and pump-retaining ring are.
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Run the tank below a quarter full to make handling easier and minimise spillage
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Relieve fuel system pressure before disconnecting anything
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Disconnect the battery
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Remove the rear seat base to access the in-tank pump cover
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Disconnect the fuel lines and electrical connector at the pump
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Unscrew the retaining ring — note that the D2 cap turns clockwise about 5 mm to release, opposite to most other VAG cars
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Carefully lift the assembly out, keeping the float arm clear of the tank opening
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Rebuild on a clean workbench using every component in the kit
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Reinstall and pressure-test before reassembling the interior
Pro tip: The retaining ring is often seized after two decades. Apply penetrating oil generously before attempting to turn it, and use the correct C-spanner — improvised tools will damage the plastic ring and turn a 3-hour job into a 6-hour job.
How long should a properly repaired pump last?
With a glass-fibre reinforced cap, new seals and OEM-spec hoses throughout, you should expect the repair to outlast the rest of the car. The reason the original failed was specifically the unreinforced plastic — solve that, and the assembly has no other inherent weakness.
Frequently asked questions
Will this kit fit my 4.2 V8 / 3.7 V8 / 2.8 V6 A8?
Yes. All D2-platform A8 and S8 cars (1997–2003) use the same in-tank pump architecture and the same cap. Engine displacement does not change the fitment.
Will this fix my fuel-pressure issue too?
If your cracked cap has caused a pressure-loss issue, repairing the cap and seals will restore the system's ability to hold pressure. If the pump motor itself is also worn, you may need a pump replacement in addition — but in most cases the cap is the sole failure.
Is the new cap really stronger than the original?
Yes. The original Audi cap was not glass-fibre reinforced. Our replacement is. This is a meaningful materials upgrade, not a marketing claim — the reinforcement adds significant tensile strength and stress-crack resistance to the polymer matrix.
How quickly do you ship?
Orders are dispatched from the EU within 24 hours on business days, with tracked delivery worldwide.
Ready to fix it properly?
Shop the Audi D2 A8 / S8 Fuel Pump Repair Kit — replaces OEM 4D0298087B and D24D0298133C. Injection-moulded, glass-fibre reinforced, complete with every seal and fitting you need.