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Chevrolet Lacetti stalls at idle during transient engine operation

Chevrolet Lacetti stalls at idle during transient engine operation 1
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The client came up with the following problem: the Chevrolet Lacetti car stalls at low gas, during transient processes in the engine when driving in bumps, holes. According to the client when driving on the highway, no problems are felt.

Chevrolet Lacetti stalls at idle during transient engine operation 2

While the client rode to me to the workshop stalled six times in puddles and pits (the road in the spring really becomes difficult to pass)

For myself, outlined the following algorithm of work:

a) scanner diagnostics of the engine;

b) pressure testing of the intake tract;

c) fuel system diagnostics;

e) reconciliation of timing marks, the correct installation of the master disks with an oscilloscope (the owner claimed that the belt was changed in September, and therefore he began to check. Car runs are small)

Inspection of the engine compartment: the gas pedal cable is loose, as expected, there was a significant backlash. Oil in the area of ​​the candle caps. As I understood from my experience and my colleagues in other workshops, such a problem is common on these cars, even the sealant does not save.

I connected the scanner on an unoccupied car. No errors were found, even saved.

Chevrolet Lacetti stalls at idle during transient engine operation 3

The first thing that seemed strange was opening the gas pedal at 8..9 percent when the damper was completely closed. Moreover, after each close, sharp percentages were different, fluctuating within plus or minus percent. Filtering the information received, I continue to check (the fact is that there are systems where, with the throttle fully closed, the throttle position sensor (TPS) shows up to 18 percent.

Started a car. There is a problem with the exhaust, judging by the sound coming from somewhere below, and the presence of white smoke.

Chevrolet Lacetti stalls at idle during transient engine operation 4

The fuel correction deviation is striking, and it changes abruptly. Perhaps there is air leakage, and the oxygen sensor is trying to compensate for it, bringing it to a ratio of 14.7 / 1.

Listening to the engine, I heard a barely perceptible hiss in the intake zone, moreover, it either appeared or not.

Sealed the intake duct near the air filter, connected the smoke nozzle.

If the video is not entirely clear, then the smoke has gone out from under the sealing rings of the intake channels of the collector. I thought about the nozzle o-rings and the valve cover, but no: the valve was normal, and the smoke came in a continuous blanket from below.

Diagnostics of the fuel system is carried out through adapters with the analysis of the fuel line, a special fitting from the factory is not provided.

Chevrolet Lacetti stalls at idle during transient engine operation 5

During the diagnosis, the clogged fuel filters, the presence of leaks in the nozzles, the serviceability of the fuel pressure regulator are checked.

The pressure was kept at about 4.2 bar in all modes. When turning off the ignition did not fall.

Oscillography of sparking was carried out by an inductive ruler, by touching the BB wires with a sensitive element of the ruler.

Chevrolet Lacetti stalls at idle during transient engine operation 6

No malfunction was found: accumulation time, high-voltage breakdown, spark burning shelf, and damped oscillations were normal on all cylinders.

I checked the timing of the timing and the correct installation of the master disks, based on examples from the library of waveforms taken from the site https://injectorservice.com.ua. In my case, it was not Chevrolet Lacetti that was found, but there were others that I nevertheless focused on. I don’t think that their concept of marking and sensors reading them changes much..

Chevrolet Lacetti stalls at idle during transient engine operation 7

Chevrolet Lacetti stalls at idle during transient engine operation 8

I connected the probes to the crankshaft and camshaft sensors, started the engine:

Chevrolet Lacetti stalls at idle during transient engine operation 9

Comparing with the standard, I come to the conclusion that everything is fine with the marks.

I decided to remove the pipe and check the throttle, because the mechanism was constantly making some strange sound. Photos from the intake side:

Chevrolet Lacetti stalls at idle during transient engine operation 10

I came to the conclusion that, due to the lack of the necessary clearance, the car stalls just at idle speed. The transitional mode such as “low gas – gas discharge – low gas” for the car is quite stressful, so such deposits immediately affect the work as a whole.

He cleaned the dirt, collected everything back. Started up, everything seems to be fine, but at the first gas-tightening, the revs become about 2300 and do not fall below. I was very surprised, like I did nothing special, but such a result. Drowned, started, warming up. I press on the gas – again 2300. I tried to spray in a throttle with a quick start – the speed is falling. I read on the Internet what and how. It turned out that after any operations with the throttle it is necessary to carry out adaptation. Fortunately, VAG.KKL was already bought from me and the necessary program was installed. You can’t give the car back to the client.

Chevrolet Lacetti stalls at idle during transient engine operation 11

The throttle rebuilt, and the revs began to stay in accordance with the norm.

Kurakhtanov Igor
© Legion Avtodata

Kostroma, Maly lane, 10
+7 (963) 930-18-21
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autodiagnostic44.ru

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