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Audi 80 B3 2.0 115HP Mechanical Injection: Starting Issues, Gas First, Fuel Pump, Flow Meter

bartekp5555 10041 11
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  • #1 17009310
    bartekp5555
    Level 2  
    Posts: 4
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    Board Language: polish
    Hello. I have a problem with the Audi 80 B3 2.0 115KM. In order for the car to start, you need to start it on gas first and if it catches up (but will not start, only after a longer spin of the engine), switch to petrol. However, it will not start on gasoline, but must first get gas. The fuel pump is heard as it says and the flow meter can be connected or disconnected, there is no difference. Should the car go out with the flow meter disconnected?
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  • #2 17009500
    helmud7543
    Level 43  
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    Flow meter and mechanical injection? Write the engine designation or give photos because I am not sure if there is any electronic control there. What is the LPG installation?
  • #3 17009545
    Krzysztof Kamienski
    Level 43  
    Posts: 21874
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    Board Language: polish
    helmud7543 wrote:
    Flow meter and mechanical injection?
    Yes, Bosch K - Jetronic. Same as Porsche 924. Check the automatic choke system - solenoid valve and bimetal.
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  • #4 17009869
    bartekp5555
    Level 2  
    Posts: 4
    Rate: 1
    Board Language: polish
    Audi 80 B3 2.0 115HP Mechanical Injection: Starting Issues, Gas First, Fuel Pump, Flow Meter

    Added after 6 [minutes]:

    Could it be the fault of the stepper motor?
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  • #5 17009910
    Doktorr
    Level 35  
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    There is no stepper motor here. Possible causes of starting problems are: too low fuel pressure, damaged or badly adjusted damper, damaged contact on the flap. Gas incorrectly fitted.
  • #6 17009956
    Anonymous
    Anonymous  
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  • #7 17010359
    bartekp5555
    Level 2  
    Posts: 4
    Rate: 1
    Board Language: polish
    As such problems with starting, she does not just start immediately on gasoline, but at the beginning, when it is cold, turn on gas and if I get it, then switch to gasoline and go. The gas itself will not fire when it is cold. Are you sure there is no stepper motor, I think there is.
  • #8 17010368
    Krzysztof Kamienski
    Level 43  
    Posts: 21874
    Help: 2029
    Rate: 5126
    Board Language: polish
    bartekp5555 wrote:
    stepper I believe there is.
    It seems wrong to you. I have a Porsche with this engine, luckily I didn't think to install LPG installations. So I know what and how it works there.
  • #9 17010400
    bartekp5555
    Level 2  
    Posts: 4
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    Board Language: polish
    Audi 80 B3 2.0 115HP Mechanical Injection: Starting Issues, Gas First, Fuel Pump, Flow Meter

    What is this marked in a red circle?
  • #10 17010436
    Wawrzyniec
    Level 38  
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    Board Language: polish
    Ordinary motor with a piston on the axis which moves depending on the angle of rotation of the motor and the return spring. The angle of rotation of the motor shaft depends on the applied voltage. I had the same in the same car, only with a 2l 16V 150KM engine on full, mechanical injection, also gassed. Except for the hatch locking up after each sneeze, it worked flawlessly.
  • #11 17010507
    Anonymous
    Level 1  
  • #12 17011312
    Anonymous
    Anonymous  
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Topic summary

✨ The discussion revolves around starting issues with an Audi 80 B3 2.0 115HP equipped with mechanical injection. The user reports that the vehicle only starts after initially running on gas and then switching to petrol, indicating potential problems with the fuel system. Responses suggest checking the Bosch K-Jetronic system, including the automatic choke, fuel pressure, and the central starting injector. The absence of a stepper motor is confirmed, with emphasis on the importance of the idle speed valve and the flow meter's functionality. Suggestions include verifying the operation of the starting injector and ensuring the fuel pump relay activates during starting. Various components such as the coolant thermistor, harness, and fuel distributor are also highlighted as potential points of failure.
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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

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?

  1. Cold engine: feed starter injector briefly with 12 V, then crank.
  2. Verify fuel pump relay latches from ignition pulses while cranking.
  3. If still no start, test power to the blue starter injector and the control switch/ECU. [Elektroda, 266564, post #17011312]
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