PROBLEM JOBS
Head scratching nuisances
Why it’s not always a safe bet fitting cheap parts Stephen Kasapic tells GW how he tracked a fault down to a newly fitted aftermarket part of unknown origin.
Job SHEET Vehicle: Alfa Romeo 156 Twin Spark. Problem: Flat spot when cold but doesn’t show any fault codes. History: Vehicle has been fitted with new air flow meter by another garage.
THE Alfa had a new air flow meter, just a few hours old and I was asked to see why it had a bad flat spot. I set up my PicoScope O2 sensor, throttle position sensor and airflow performance information data on my scan tool and went for a drive. I gave it full throttle and the O2 went lean, so I knew it needed more fuel. I knew it had a new air flow meter, so I checked the fuel pump and the pump flow was OK. The new air flow meter went to 4.454 volts, so it looked OK. I’ve scoped a few Alfa 156 air flow meters before and had a look at my Pico library to confirm good air flow meters go to about 4.4 volts with the motor hot. The new air flow meter was a lot slower to get to 4.4 volts so I had a good look at the new meter and did not see Bosch on it anywhere. I called the workshop that fitted it and asked where he got the air flow meter from. He said it was some aftermarket thing and was told it was just as good as the Bosch one. The next day I got a new Bosch Air flow meter and bingo, the car ran great again.
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