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Weekdays beginner diagnostician

Weekdays beginner diagnostician 1
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Weekdays beginner diagnostician

Without keyword

Putting knowledge into practice.

One can say in this industry, a novice, before working as a Diagnostic, he worked as an auto mechanic, while periodically studying various literature and reading articles on the Legion Avtodata website. It so happened that I read many articles by Timofey Inozemtsev (nickname tirim on the Legion forum), and did not even think that he would soon be my mentor in this difficult but interesting matter, for which many thanks to him.

Let’s start…
It so happened that from childhood I had a passion for Ford brand cars, I would even say that they are “completely turned” by this brand. Well, while not forgetting to repair the rest of the brand. And when I saw the Ford Focus 3, which pretty much broke the head of my colleagues from another shift, without hesitation, got down to business.

Briefly about the car itself: the usual 1.6 Duratec TI-VCT with two phase regulators (colloquial name) on the intake and exhaust camshafts.

CAT 6DCT250, aka Powershift. The nuance is that the engine is programmatically “decoupled” from the factory by capacity, that is 125 hp, instead of the usual 105. The peculiarity is that there are 2 catalysts, one on the 1st and 4th cylinder, the second on 2nd and 3rd. A little strange decision, I suspect that everything has been done for the sake of ecology

The customer’s complaint is this: when the engine is warm, the car “”, sometimes, after a short parking of the car, the malfunction does not appear, then it repeats. I skated like this for 2 months, the verdicts were different in three car service centers, but nobody apparently dared confirm it, but oh well. The client himself changed the candles, washed the injector and was close to changing the ignition module, but there it was..

It was surprising that there were no errors in the list of malfunction code recorder for the Engine Control Unit, deleted them before or it really was, I don’t recognize. I’ll try to see and analyze data from the scanner:

Atmospheric pressure (Baro): Shows real values ​​that correspond to atmospheric pressure (there were a couple of cars in practice when, due to unreliable contacts on the engine ECU connector, the barometric pressure was frankly lower).

The temperature of the catalysts (Cate mp1 and Cate mp2): in principle, reflect the real essence of the work on the temperature regime. Indirectly, we can assume that they are not clogged.

Of the variable data set, are I interested in the misfires themselves (Mis_Tot_CiL 1,2,3,4)? of which have not yet been observed. The values ​​of short-term (Shift 1 and 2), long-term (Long FT1) fuel corrections are close to zero values ​​at XX? which corresponds to the normal process of gas exchange in the engine, but the work of oxygen sensors provided food for thought. Here you need to stop a little and remember the principle of its operation: the usual zirconium lambda probes are installed on this car, one in front of the catalyst of the 1st and 4th cylinders, the second in front of the catalyst of the 2nd and 3rd cylinders, two more stand after it:

The sensor element is located in the exhaust gas stream. When the temperature reaches about 300 degrees, it begins to generate a voltage proportional to the oxygen content passing through it. In fact, the signal is a rapidly changing voltage from 0.1v (there is a lot of oxygen in the exhaust gases) to 0.9v (there is little oxygen in the exhaust gases).

So: when the engine temperature reaches about 90 degrees, an interesting picture arises:

In the parameters of the number of misfires (Mis_Tot_CYL 2 and 3), their manifestation in the second and third cylinders is clearly visible. And if the oxygen sensor after the second catalyst (O2S22) reacted to the depletion of the mixture in the second and third cylinders, then the sensor to the catalyst of the second and third cylinders remained “hanging” at a reference voltage of 0.45 volts. The truth, as they say, is even closer, but in order to dispel doubts, I will finally check the signal from the sensor with an oscilloscope:

As can be seen from the signal amplitude, the sensor itself is not able to respond to depletion / enrichment of the air-fuel mixture. Given the relatively low cost of the sensor itself (with us it costs about 3,500 rubles), the Client agreed to a replacement. As experience will show later, this element does not fail in isolated cases, in view of:
1) Defective batch established between 2012-2014.
2) Poor fuel.

Meanwhile, the sensor came to the warehouse, installed on the car, once again I recheck the parameters on the scanner:

I see that all testimonies are admitted, the client is satisfied, the mentor is satisfied. I’m happy. I continue to improve my practical and theoretical knowledge in this craft.

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