FAQ
TL;DR: Audi 80 B3 2.0 (115 HP) with K/KE‑Jetronic cold‑start issues often trace to 1 starting injector; "Without it, the cold engine will not start." [Elektroda, 266564, post #17011312]
Why it matters: This FAQ helps Audi 80 B3 owners diagnose hard petrol starts—especially when it only fires on LPG.
Quick Facts
- Injection type: Bosch K/KE‑Jetronic mechanical system with airflow flap and fuel distributor; no stepper motor, uses an idle valve. [Elektroda, Anonymous, post #17010507]
- Cold start uses one central “blue-body” starting injector on the manifold; verify power at its plug. [Elektroda, 266564, post #17009956]
- Quick test: briefly feed the starter injector with 12 V to check cold-start enrichment. [Elektroda, 266564, post #17011312]
- Fuel pump relay energizes only after ignition pulses during cranking; failure here mimics fuel starvation. [Elektroda, 266564, post #17011312]
- Misadjusted flap/low fuel pressure or poorly fitted LPG can prevent petrol starts. [Elektroda, Doktorr, post #17009910]
How do I fix an Audi 80 B3 that starts on gas but not on petrol?
Check three things first: the starter injector gets power when cold, the fuel pump relay latches during cranking, and airflow flap contact signals. If it then fires, adjust LPG so it doesn’t upset the fuel distributor. Quote: "Supply the starter injector briefly with 12V and try to start." [Elektroda, 266564, post #17011312]
Does this engine have a stepper motor for idle control?
No. It uses an idle speed valve, not a stepper motor. That valve is not the usual cause of your hard-start issue. The idle device is either bimetal-heated or a proportional valve depending on K vs KE. [Elektroda, Anonymous, post #17010507]
What is Bosch K/KE‑Jetronic in simple terms?
It’s a mechanical fuel injection system. Airflow lifts a flap that meters fuel via a distributor. The ECU (KE) may fine-tune, but there’s no classic electronic injector firing per cylinder. Flap position is read by a potentiometer. [Elektroda, Anonymous, post #17010507]
How do I test the cold-start (starter) injector safely?
With the engine cold, unplug and inspect the starter injector connector. Briefly apply 12 V to the injector to enrich, then crank. If it starts, diagnose its control path (thermal switch in K‑Jet or ECU in KE). Remove 12 V immediately after testing. [Elektroda, 266564, post #17011312]
Where is the starter injector and what should I see?
It’s mounted on the intake manifold and has a blue body. With a cold engine, it should receive switched power during start. In K‑Jet the thermal switch controls it; in KE the ECU does. Lack of power points to sensor, harness, or controller faults. [Elektroda, 266564, post #17009956]
My fuel pump runs; why still no petrol start?
The pump relay must energize from ignition pulses while cranking. If the relay fails to latch, fuel pressure won’t build, yet the pump may be audible. Edge case: it may only latch after the engine fires on LPG. Inspect the relay and ignition signal. [Elektroda, 266564, post #17011312]
Will disconnecting the airflow meter affect starting?
Yes. A healthy system reacts to the flap signal. If plugging or unplugging the flow meter makes no difference, suspect the flap contact, potentiometer, or wiring. Also verify damper adjustment and base fuel pressure before further tuning. [Elektroda, Doktorr, post #17009910]
What is the red‑circled component in the photo?
It’s a motorized air valve with a piston and return spring. Its position changes with applied voltage, altering bypass air and stabilizing idle. Frequent backfires can stick the hatch, but the valve itself typically works reliably when powered correctly. [Elektroda, Wawrzyniec, post #17010436]
Can an LPG installation cause hard petrol starts on K/KE‑Jetronic?
Yes. Poorly installed or tuned LPG can disturb the fuel distributor’s calibration and airflow flap behavior. Restore proper petrol operation first, then recalibrate LPG so it doesn’t lean out cold starts or block airflow paths. [Elektroda, Anonymous, post #17010507]
Which engine code fits a 2.0 115 HP Audi 80 B3 with mechanical injection?
AAD is a common 2.0 115 HP code for these cars. Confirm on your timing belt cover label or vehicle data sticker to be certain, since trims vary by market and year. [Elektroda, Anonymous, post #17010507]
What voltage should the starter injector see during cranking?
Expect switched 12 V at the injector during a cold start command. On K‑Jet this comes via a thermal time switch; on KE it’s ECU-controlled. If 12 V never appears cold, trace the sensor, harness, and controller before replacing parts. [Elektroda, 266564, post #17009956]
Is the Audi 80 B3 similar to the Porsche 924 system?
Yes. Both used Bosch K‑Jetronic mechanical injection architecture. Components differ by engine, but the airflow flap and fuel distributor principle match. Use Porsche K‑Jet references cautiously due to calibration differences. [Elektroda, Krzysztof Kamienski, post #17009545]
Will a faulty flap contact or damper adjustment block cold starts?
Yes. A failed flap contact or misadjusted damper can prevent enrichment and proper metering at crank speed. Combine this with low fuel pressure and starting becomes very difficult, especially in cold weather. Inspect and set these before ECU work. [Elektroda, Doktorr, post #17009910]
What are the baseline specs for this topic’s car?
Audi 80 B3 with a 2.0 engine rated at 115 HP, running mechanical injection and LPG. The reported symptom: starts on gas first, then runs on petrol, with no change when unplugging the flow meter. [Elektroda, bartekp5555, post #17009310]
Quick 3‑step cold‑start diagnosis before swapping parts?
- Cold engine: feed starter injector briefly with 12 V, then crank.
- Verify fuel pump relay latches from ignition pulses while cranking.
- If still no start, test power to the blue starter injector and the control switch/ECU. [Elektroda, 266564, post #17011312]
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