See the root


How they managed to diagnose and, in the end, defeat the insidious defect, says the head of the brand technical center in Kazan.

Vladimir DEMIDOV

The problem of "start-up-not start" exists, probably, since the invention of the car.

With the advent of reliable and relatively inexpensive "Nexia" from Uzbekistan, the owners of the "Lada" and "Samar" who had resettled on them finally felt like people, but at the same time realized that their "Zhiguli" experience is of little use for a new car. And if something happens, then there is only one road - to a car service.

The first time we encountered Nexia, a company that sometimes refused to start, we encountered in the fall of 1997. According to the owner (it’s “from the words”, since it was much later to see a car that does not start the engine), the car put him in an awkward position a couple of times, but after a few minutes (obviously, while the owner wiped his headlights, windows and kicked wheels) started up as if nothing had happened. That case was not an isolated one. In cars suffering from such an ailment, the engine could refuse to start at any time - after a long parking or after a short one, in bad weather or in good weather, in a garage or in the fresh air. Just as unexpectedly, he could stop fooling and work for a week, a month for normal, and then it all started again. It happened that Nexia was dragged to us in tow, the master got behind the wheel, and … the engine started, as they say, with a half kick! This problem brought owners to a white heat, they began to be afraid of their cars.

In a word, we were dealing with a typical "floating" defect - one of those that can make a car service specialist doubt the correctness of the choice of a profession. The rich (by then three years) experience working with Daewoo cars from Korea could not help - they did not encounter such a defect, they always started.

It was necessary to repair such cars (how can a car be repaired?) Guided by the principle that “electronics is the science of contacts”, that is, disconnecting and connecting electrical connectors, cleaning, blowing … Sometimes this helped, more often it didn’t. But statistics, the great of science, did its job - the overall picture began to emerge. The engine of defective cars was not started due to the absence of a spark on the ignition coil, and a “plus” was supplied to it, that is, pulses were not formed in the primary winding. If you try to start the engine “from the pusher” at this moment, then it starts instantly. These two factors were a necessary and sufficient condition for the subsequent recommendations to be applied. But first, a little theory.

The schematic diagram of the Nexia ignition system is shown in the figure. A magnetoelectric pulse sensor (not to be confused with a Hall sensor) and an electronic module (switch if you want) are located in the distributor housing. The pulse sensor consists of a magnetized rotor, integral with the distributor shaft, and a stator, which includes two pairs of poles and an induction coil, in which an electromotive force (EMF) with a frequency of 8 Hz and an amplitude of about 2 V is induced in the starter mode. The electronic module converts these pulses are rectangular in amplitude of 12 V and feeds them into the primary winding of the ignition coil. After starting the engine, the electronic control unit (ECU) is also included in the ignition system, which is responsible for changing the ignition timing depending on the engine operating conditions.

It was most logical to assume that the cause of all ills is precisely in the module. After all, the word "switchboard", uttered with the corresponding epithets in the company of motorists, immediately gives rise to sympathetic nods and a sea of ​​gloomy memories. However, replacing the switches on problem cars with a promise to return the money if the defect does not disappear, led to a refund and counter questions: well, then what? But really - what if the electronic module, and the ignition coil, and the computer are checked and working normally, what remains? Is the sensor really? No, I don’t feel like “thinking of him”, because I’m primitive to the limit. In it, the only part that can fail is an induction coil, and even that is a plastic “bobbin” with a 0.1 mm diameter copper wire wound around it. The Nexia car repair manual instructs to check the coil’s performance to measure its resistance, and if it is in the range of 500-1500 Ohms, then everything is in order. We measured this resistance in dozens of coils, and always it was in the range of 750-800 Ohms.

His Majesty Chance finally helped put everything in its place. We got the same car, which had the necessary and sufficient sign of a malfunction, but it did not start from the starter at all! Examining this car, we found that the amplitude of the pulses at the contacts of the induction coil is very small (about 0.2 V), which is clearly not enough for the normal operation of the electronic module. (By the way, the resistance of this coil was 750 Ohms!)

I had to recall the section “Electromagnetic induction” from school and university physics courses: the EMF of induction of a coil with a wire is directly proportional to the rate of change of the magnetic flux (in our case, the speed of rotation of the engine crankshaft at start) and the number of turns of the coil. It is rather troublesome to count the turns, it is much easier to estimate their number by measuring the coil inductance. Our measurements of the inductance of the latter in defective cars showed that they have this parameter 10-15% lower than that of obviously suitable ones, and that of the Nexia coil, which did not start at all (God forbid “health”), by 26 % It follows from this that during start-up the engine should rotate as quickly as possible. This fact also explains why a car with a substandard coil starts up "from the pusher" - because the engine speed in this case increases significantly. Therefore, the condition of the battery, the connection of power wires, the corresponding oil in the engine in winter - all this is very important.

In practice, we replaced induction coils in about fifty cars (3-4% of those sold by our company). None of the owners of these machines contacted us again with this defect.

Now the traditional question is: who is to blame? We do not have reliable information on this subject, but I think that with an increase in the component production program for the UzDeu plant in Uzbekistan, the technological process for the manufacture of induction coils could be disrupted at some of the neighboring enterprises of the Daewoo Motor. In combination with other unfavorable factors, this made the owners of problematic machines, and we, along with them, pretty worried. My assumption is confirmed by the fact that there are no similar problems with the Nexia from Korea and the Daewoo Espero, which have exactly the same ignition system.

Of course, when we first encountered this extraordinary phenomenon, we turned to the automobile manufacturer for help. And they got about the following answer: "We did not have the described cases, try changing the electronic module." Then it became clear in whose hands the salvation of the drowning. Although in fairness I must say, recently this defect is becoming less common. Obviously, something has changed for the better.