Fuel System

Factory fuel-supply service for the 944: replacing the fuel filter and leak-checking the injection lines, measuring the electric fuel pump's delivery rate, removing and installing the pump and the tank, the fuel-system line routing, and the active-carbon evaporative canister. Includes the delivery-rate test value and the pump capped-nut torque; the fuel-pressure and CO setpoints live on the injection-adjustment page.

Step-by-step removal and installation of the air filter housing and air flow sensor on 944 and 944 Turbo models, with separate procedures for each variant.

How the DME relay works on 1985.5 and newer 944s, how to diagnose failures, how to test it with a multimeter, and how to repair cracked solder joints or replace the internal diode.

How the fuel supply, fuel return, and primary vacuum lines route on 16V normally-aspirated 944S and 944S2 models, with a note on active-carbon-tank routing.

How the fuel supply, fuel return, and primary vacuum lines route on 1985.5 and newer 8V normally-aspirated 944 models — supply, return, and the main vacuum connections.

How the fuel supply, fuel return, and primary vacuum lines route on the 944 Turbo, with a note on active-carbon-tank routing.

Procedure for removing and installing the in-line fuel filter on 944 models, including how to safely pinch the inlet hose and check for leaks.

Factory testing-and-adjusting procedure for the 8-valve L-Jetronic / DME fuel injection: idle-speed and CO setpoints by market, the fuel-pressure check, and how to adjust idle and CO — including the air-flow-sensor mixture correction on catalytic-converter cars. Covers early 944, the 1985.5-and-later 944 / 924S, and the 2.7-litre M44.11/12.

Step-by-step removal and installation of the fuel rail and individual fuel injectors on 944 and 944 Turbo models, including torque specifications.

Porsche and Bosch part numbers, rated flow rates, and winding resistance for fuel injectors used in all 944 and 968 variants, covering 1982–1995.

How to test fuel rail pressure at rest, at idle, and after a 20-minute leakdown on 8V and 16V 944 models, with full specification tables.

How to distinguish the fuel pressure regulator from the fuel damper, identify failure symptoms, test with a pressure gauge, and replace the FPR with part numbers covering all 944 and 968 variants.

How to measure fuel pump output volume over 30 seconds using a relay jumper and measuring container, with delivery rate specifications by pump type.

How to safely depressurize the fuel system, remove, and install the Bosch in-tank fuel pump on 944 models, with fuse locations for each generation.

How to drain the fuel tank, access and clean or replace the suction strainer on the fuel tank outlet, and reseal with a new O-ring — with part numbers for all 944 variants.

Two fabrication methods for making a metric-to-SAE adapter that allows a 1/4-inch flare fuel pressure gauge to connect to the 12 mm × 1.5 thread 944 fuel rail end cap.

Systematic procedure for isolating the cause of a fuel system leakdown failure — distinguishing between a leaking FPR, leaking pump check valve, or leaking injector(s) using hose clamps and a pressure gauge.

How to diagnose and replace the DME-controlled idle control motor (idle stabilizer) on 1985.5 and later 944s and all 944 Turbos, including removal with or without intake manifold disassembly.

How to adjust idle speed on 8V 944 and 944 Turbo models using the throttle body idle screw, with idle RPM specifications by market and instructions for defeating the idle stabilizer.

Complete removal and installation procedure for the 944 and 944 Turbo intake manifold, including torque specifications and notes on gasket orientation.

How the O2 sensor works in single-wire and three-wire heated versions, how to test its response with a voltmeter, and factory Porsche and Bosch part numbers for all 944 and 968 variants.

How the throttle position switch (TPS) works on the 944 8V, 944 16V (S), and 944 Turbo, including resistance testing at the DME/KLR plugs and adjustment procedure after replacement.

Terminal-level diagnosis of fuel supply problems on Motronic 944s and 968s — why the fuel pump won't start during cranking, how to bypass and test the Fuel Pump / DME relay, and how to check the speed sensor, reference sensor, and starter-solenoid cranking signals the DME needs.