Audi RS4
The BNS is a high-revving V8 with 420 PS at 7,800 rpm and an 8,250 rpm redline — piston speed at rated rpm: 25.4 m/s, identical to a 2012 F1 engine. FSI direct injection without port injection leads to the most aggressive carbon build-up of all 4.2 FSI variants: according to specialist workshops, no RS4 B7 reaches its rated power on the dyno — measured outputs were 347 to 385 PS instead of 420. Mechanical intake cleaning (BEDI) every 15,000–20,000 km restores power, chemical cleaning is not sufficient. Oil cooler connections corrode through galvanic corrosion (aluminium against steel) and are almost always seized at 15+ years of vehicle age. Water-cooled alternator costs four figures to replace. Oil changes every 10,000 km with 5W-40; at high oil consumption use 15W-50. Compression ratio 12.5:1 requires Super Plus fuel.
420 hp NA V8, manual — the holy combination
High-revving V8 to 8,250 rpm, six-speed manual, quattro. This combination will never exist again. The B7 is the only RS4 purists take seriously. Sounds like a small Ferrari, lasts like an Audi. Prices climbing double digits annually.
Engine Weaknesses 8
The main problem of the BNS: FSI without port injection heavily cokes the intake valves. Specialist workshops measure 347–385 hp instead of the stock 420 hp. Mechanical BEDI cleaning every 15,000–20,000 km needed; chemical cleaning is insufficient.
Symptoms: Gradual power loss over months, rough idle, increased fuel consumption, sluggish throttle response in the upper rev range. Often only measurable on a dyno.
The timing chain sits on the gearbox side. Guide rails and tensioners wear; replacement requires engine-gearbox separation. With consistent oil changes (max. 10,000 km) the chain lasts significantly longer. Cold-start rattling is the warning sign.
Symptoms: Rattling on cold start that disappears after warm-up. At advanced wear, permanent chain rattling and engine warning light.
Four camshaft adjusters wear from oil-deficiency-related abrasion. Oil quality and short change intervals (max. 10,000 km) are critical. Rattling on cold start and fault codes are typical signs.
Symptoms: Rattling on cold start in the camshaft area, power loss at low rpm, engine warning light with camshaft fault codes.
The oil cooler connections (aluminium) suffer from galvanic corrosion with the steel lines. After around 15 years the connections are almost always seized — even weeks of penetrating oil often makes no difference. Oil cooler and both lines must be replaced completely.
Symptoms: Oil weeping at the oil cooler, seized fittings when attempting maintenance, whitish corrosion marks at the oil cooler connections.
The BNS has a water-cooled alternator — unusual and expensive to replace. The combination of water cooling and high thermal load in the engine bay makes this component more failure-prone than conventional alternators.
Symptoms: Battery warning light, charging voltage too low, electrical consumers drop out, coolant loss at the alternator.
The FSI high-pressure pump can fail after 80,000–100,000 km. Without sufficient fuel pressure the engine runs in limp mode with a clear power loss.
Symptoms: Engine stuttering under load, power loss, engine warning light with fuel pressure fault codes, difficult starting.
The DRC system (Dynamic Ride Control) connects the shock absorbers diagonally via hydraulics. When a leak develops, the system loses fluid; complete replacement costs 3,000–5,600 €. Alternative: disable with Bilstein B8 sports dampers, registration-free and cheaper.
Symptoms: Increased body roll in corners, oil traces on the shock absorbers, uneven spring travel, DRC warning in the instrument cluster.
With a sporty driving style and frequent high-revving to 8,000+ rpm, 1 L/1,000 km oil consumption is normal and not a defect. Specialist workshops recommend switching to 15W-50 to reduce oil quantity drawn into the induction system via the crankcase breather.
Symptoms: Falling oil level between services, faint oil smell at high loads. When buying: ask whether the previous owner needed to top up oil.
Vehicle Weaknesses 6
On the 2.0 TDI the hexagonal shaft of the oil pump drive can snap, causing immediate oil pressure loss and engine damage. Preventive replacement is recommended.
Airbags manufactured by Takata can deploy with excess pressure and propel metal fragments. Worldwide recall campaign.
Control arms and tie rod ends wear prematurely. Clunking and rumbling on poor surfaces. The multi-link front axle is maintenance-intensive.
Defective ignition coils can immobilise the engine or cause severe running roughness. Mainly affects 1.8T and 2.0 TFSI engines.
From model year 2004 Audi used partial bonding instead of full galvanisation. Wheel arches and sills are vulnerable to rust, especially on older examples without cavity protection.
Rear wheel bearings fail regularly on the A4 B7. Quattro models show increased wear.