To help smooth the math channel I’ve added a lowpass filter to the formula. You can see the initial gulp of air from the engine as the throttle is opened, followed by the gradual rise in MAF as the engine RPM increase during a snap throttle event.
Math channel showing MAF response to snap throttle. We started the engine and the results spoke for themselves: We crossed our fingers and turned the ignition on – no EML. As we already had the leads in place we placed a jumper lead between the battery earth and the MAF earth terminal. To be completely confident with our diagnosis we had one last thing to try: to provide the MAF sensor with a direct earth. Perhaps there is something going on that we don’t know about? How long would we have to wait? “We have one on the shelf and can drop it out today if you need it.” Not something you hear every day and it does make you wonder why a dealership would be holding stock of a £1200 ECU. The answer to our next question, however, was somewhat more surprising and one that raised a few eyebrows. £1200 +VAT! Well, I guess that was to be expected. Happy that this was indeed the case, we phoned the local dealership for a price and had to sit down. Because it is not the most common component to replace, we checked and doubled checked our connections and the tools to be 100% certain that there was no way an earth signal was sent from the ECU to the MAF sensor. No one ever likes to condemn an ECU because if you fit it and the fault is still there you are now the proud owner of a £1000 piece of metal. Now we were left with one last component, the PCM. Just to make things more complicated, the resistance was minimal in the wire measuring with 0.2, and a check against the other wires and to ground all resulted in an open circuit. I don’t think I’ll ever get used to being upside-down in the footwell of a car, with a torch between my teeth, a back-pinning probe in one hand, while the other hand wrestles with a wiring loom that feels like it was moulded after it was fitted to the car. Finding the pin at the ECU was easier said than done. We turned our focus to the earth circuit. In the waveform above we have nothing present. With no real idea as to what is going on, there should be something. With a timebase of 2 s/div, we would expect to see a block of yellow. Not only this, but the MAF sensor is a digital type which is obviously not present on channel D. This is not correct and it may even be open or at least at a very high resistance. We can see the battery voltage with the engine running at 14.7 V, but the earth, which is supplied from the ECU, is at 12 V. Be careful when fitting pattern parts as the sensors will vary and can have adverse effects on the signal. In this instance, it hadn’t been sold as a genuine part but everything looked the same, only the manufacturer numbers had been ground off. The replacement sensor was a pattern part and not a genuine sensor, which seems to be a growing trend. Luckily, the customer had asked to have the old one back when replacing it didn’t work. After further chats with the customer, we learned that the vehicle had already been fitted with a replacement MAF sensor – the plot thickens. In this instance there was an issue with one of the pins in the plug, giving us the impression that it had already been looked at somewhere else. By using the male ends we can check to see if there is any issue with the connection between the pins. A great tip here is to use a breakout lead to check the resistance of the pin. So, first things first, we checked the sensor plug for security and pin integrity. #Max airflow sensor code
It had been brought in as the EML was on with the fault code P0102 Mass Air Flow MAF Circuit Low. The vehicle was a 2014 B-Max, 1.0L, 3-cylinder, turbocharged petrol engine. The fact that it is a 4-wire type that has a 12 V supply from the same fuse that the fuel pump gets its supply from makes it intriguing. Automotive Application Specialist, Ben Martins, was recently asked to join an old work friend to take a look at a new type of air flow sensor that, for now, has only been seen on the Ford EcoBoost engine.
0 kommentar(er)
