The Audi RU is a 1,781 cc inline-four petrol engine produced between 1984 and 1991. It features a single overhead camshaft (SOHC), 8-valve configuration, and Bosch Mono-Motronic fuel injection system. Designed as an evolution of the MU engine, it delivered 66 kW (90 PS) at 5,800 rpm and 137 Nm of torque at 3,500 rpm with improved emissions control.
Fitted to the Audi 80 B2 and Audi Coupé B2 models, the RU engine replaced the MU with integrated ignition and fuel management via the Mono-Motronic system. This consolidation reduced component count and improved cold-start reliability. It met European emissions standards through the use of a catalytic converter and oxygen sensor feedback loop, complying with Euro I regulations.
One documented update occurred in 1987, when Audi revised the cylinder head casting to improve coolant flow and reduce localized overheating. This change, referenced in Audi Technical Service Bulletin 0187.03, also included recalibration of the idle air control valve and updated ECU mapping. No major structural changes were made to the block or valvetrain during its production run.
All production years (1984–1991) meet Euro I emissions standards with catalytic converter (VCA UK Type Approval #VCA/EMS/5679).
The Audi RU is a 1,781 cc inline-four SOHC petrol engine designed for compact Audi sedans (1984–1991). It integrates Bosch Mono-Motronic fuel and ignition management into a single ECU, improving emissions and drivability over its predecessor. Built on the EA827 platform, it prioritizes serviceability and durability in urban and highway applications.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,781 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-4, SOHC, 8-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 81.0 mm × 86.4 mm | |
| Power output | 66 kW (90 PS) @ 5,800 rpm | |
| Torque | 137 Nm @ 3,500 rpm | |
| Fuel system | Bosch Mono-Motronic integrated fuel and ignition | |
| Emissions standard | Euro I (with catalytic converter) | |
| Compression ratio | 9.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Timing belt (replaced every 60,000 km) | |
| Oil type | SAE 10W-40, API SF/CC | |
| Dry weight | 138 kg |
The RU engine offers improved emissions and cold-start behavior over the MU due to the Mono-Motronic system, but remains sensitive to vacuum leaks and aging sensors. The timing belt must be replaced every 60,000 km to prevent valve damage, as it is an interference design. SAE 10W-40 mineral oil is sufficient, though regular changes prevent sludge buildup. Fuel quality is less critical than in modern engines, but lead-free petrol (RON 95) is required for catalyst protection. No major revisions occurred after 1987, so parts are generally interchangeable across the production run.
Oil Specs: Requires SAE 10W-40 meeting API SF/CC specification (Audi SIB 0187.03). Supersedes earlier mineral oil standards.
Emissions: Euro I certification applies to all 1984–1991 models with catalytic converters (VCA Type Approval #VCA/EMS/5679).
Power Ratings: Measured under DIN 70020 standards. Output consistent across all markets due to non-turbo design.
Audi Technical Information System (TIS): Docs A18045, A18211, SIB 0187.03
VCA Type Approval Database (VCA/EMS/5679)
ISO 1585:1976 Road vehicles — Engine test code — Net power
The Audi RU was used across Audi's B2 platform with longitudinal mounting and no licensed external usage. This engine received minor adaptations-cylinder head cooling revisions in 1987 and updated ECU calibration-and from 1988 onward, the Audi 80 facelift models retained the RU in base trims, creating limited interchangeability with later ABF engines. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, near the exhaust manifold (Audi TIS A18045). The 7th digit of the VIN identifies the engine type ('R' for RU series). All RU engines feature a catalytic converter and single exhaust manifold. Critical differentiation from MU engines: RU uses Bosch Mono-Motronic with integrated ECU and idle air control valve, while MU uses L-Jetronic with separate ignition distributor. Service parts require chassis number verification—timing belts for pre-1987 models differ slightly due to pulley redesign (Audi SIB 0187.03).
The RU's primary reliability risk is timing belt failure due to age or missed service intervals, with elevated incidence in high-mileage examples. Audi internal service reports from 1991 noted a significant number of interference-related valve damage cases, while UK DVSA MOT records show increased exhaust system failures in high-mileage units. Extended oil change intervals and poor fuel quality accelerate wear, making scheduled maintenance critical.
Analysis derived from Audi technical bulletins (1984-1991) and UK DVSA failure statistics (1985-1995). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about AUDI RU.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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