More older Porsche 928s are coming back to life. I'm assisting an independent shop with an early 1980s Porsche 928 that has L-Jetronic fuel injection. A known good tester L-Jet module was sent and the engine will not start, so more diagnostics is needed. I created this overview to assist such diagnostic testing.
Where the newer 1985 - 1995 928s (as well as Euro/ROW 1984) use digital based control where the engine can start with no connection to the coolant temperature sensor and mass airflow sensors, the earlier L-Jetronic must have valid voltages at the module before injection will start. I outlined these connections and how to verify the circuits.
1980 - 1984 L-Jetronic Porsche 928 No-Start Diagnostics
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Porsche 928 L Jetronic Diagnotic Testing 2026_0606.pdf- (1.6 MiB) Downloaded 2 times