Description

Ford Sierra RS Cosworth 1985 Service Manual

If you have ever tried to rebuild a Cosworth YB engine using a chilton or haynes, you already know the pain. Those books skip the boost pressure control logic, leave out the cylinder head bolt sequence, and give you a generic wiring diagram that matches nothing. That is why you need the actual Ford Sierra RS Cosworth 1985 Service Manual. This is the 77-page technician training document Ford issued in October 1985. It was written for the guys who had to keep these cars on the road when they were new. It is not a reprint of a reprint. It is the real thing.

Part A – Engine: The Cosworth 16-Valve Unit

Section 1.1 breaks down the cylinder head, front belt drive, crankcase assembly, and the oil pump with lubrication circuit. Page 26 contains the critical notes on cylinder head disassembly and assembly. If you do not follow the bolt loosening sequence on that page, you will warp the head. I have seen it happen. The manual also covers the crankcase ventilation system and the specific sealant Ford used on the oil pan. Aftermarket manuals treat this engine like a pinto. This one treats it like a competition motor — because it is.

Electronic Engine Management: Fuel, Air, Ignition

Section 2.2 covers the fuel system, the air system, and the ignition system. That is not a typo — the manual lists all three under the same subsection number because they work together as one unit. The Fuel section includes the injector flow rates, the fuel pressure regulator specs, and the cold start valve operation. The air system describes the idle speed control and the vane air flow meter. The ignition system shows the EDIS module pinouts. If you try to diagnose a no-start using a generic manual, you will chase ghosts. This manual gives you the sensor voltage ranges and the resistance checks for the crankshaft position sensor. You can find that data in the system sensors and actuators section, 2.3.

Turbocharger and Boost Pressure Control

Part A, section 3.1 is a general description of the Garrett T3 turbo. Section 3.2 covers the boost pressure control system — the wastegate actuator, the boost control solenoid, and the overboost fuel cut. This is where most aftermarket manuals fail. They tell you the wastegate opens at 8 psi but do not explain the electronic bleed that Ford used to limit boost in first and second gear. The manual has a pressure diagram that shows exactly how the ECU modulates the solenoid. If you are tuning or rebuilding the turbo system, you want this chapter. It also lists the torque for the turbo-to-manifold nuts — 305 lb-in, if I remember correctly from the technical data on page 53.

Transmission and Rear Axle: Disassembly Notes

Part B covers the Transmission — the MT75 five-speed. Section 1.3 is titled “Important Notes on Disassembly & Assembly.” That section tells you which snap rings are one-time use and which bearings need preload shims. It also shows the power flow path through the synchronizers. If you are rebuilding this gearbox, you need the clearance specs from the technical data on page 64. The rear axle section lists the diff ratio (3.62:1 for the standard car) and the LSD rebuild specs. Missing a shim thickness will cause howling. The manual does not let you guess.
For more on the MT75 design, see Manual Transmission on Wikipedia.

ABS and Body Features: What the Manual Covers

Part D covers the Teves anti-lock braking system. The technical data on page 73 gives you the wheel speed sensor gap, the hydraulic pump pressure, and the control unit diagnostic codes. The ABS chapter explains how the system uses the speed sensors at each wheel and the modulator valves. If your ABS light is on and you only have a generic wiring schematic, you will replace parts until you go broke. This manual tells you to check the relay first, then the sensor resistance (800–1200 ohms), then the controller pin voltages. Part E covers the body features — the rear wing, the wheel arch extensions, and the interior. It lists the wheel torque for the 15×7 alloy wheels: 85 lb-ft. That is not a suggestion.

Why This Manual Beats Any Aftermarket Book

This is a Ford original — not a photocopy of a copy. The diagrams are clear, the torque values come straight from the engineering release, and the procedures include warnings about special tools (like the flywheel holder tool 21-009). Aftermarket manuals often reuse diagrams from the regular Sierra and miss the Cosworth-specific parts. The 77 pages are dense with actual content. There are no filler sections about how to change oil. Every page addresses something specific to the RS Cosworth: the boost control solenoid, the knock sensor, the water-cooled turbo housing, the unique crankcase breather setup. If you own one of these cars, you need this manual on your bench.

Does this manual cover the turbocharger rebuild?

Yes, section 3.1 and 3.2 describe the turbocharger components and boost pressure control, but the manual focuses on removal, installation, and system diagnostics rather than full internal rebuild. For internal clearances, you would need a separate turbo supplier spec sheet.

Is the wiring diagram included?

No.

Related manuals that pair well with this one: Ford Sierra and Escort RS Cosworth Workshop Manual, Ford Engine Management and Emission System 2.0L, and for older Ford V8s, Ford 2100, 2110, 3100, 4100, 4110 Service Manual – Pre-1975. For background on the era of this vehicle, see Automotive Industry Overview.

Stop wasting time on books that leave out the boost pressure table. Access the Factory Manual now and get the torque specs, the diagnostic procedures, and the assembly notes that will keep your Cosworth running the way Ford intended.