Maintenance case: Passat speed, increase in engine speed is not enough to troubleshoot

A 2003 Shanghai Volkswagen Passat with about 180,000 km, AWL1.8T engine and five-speed manual transmission.

Maintenance case: Passat speed, increase in engine speed is not enough to troubleshoot

Owner Description: Vehicle runs normally when refueling at idle, vehicle hovering in mid-air and shifting into gear. When driving on a freeway, engine speed reaches 4000-4250rpm, and after reaching a car speed of 140km/h (on a flat road), engine speed and car speed can no longer be increased, and fuel consumption is greater. intense lately.

Maintenance case: Passat speed, increase in engine speed is not enough to troubleshoot

Failure Diagnosis: According to owner's report, service technician also requested time of occurrence of fault and changes in vehicle operation before and after fault occurred. The owner of car said that he only felt it when going up mountain from time to time, he used fourth gear to get up that mountain with little fuel and he could easily pass by.

Maintenance case: Passat speed, increase in engine speed is not enough to troubleshoot

Having listened to above description of car owner, after careful analysis, maintenance technician believes that malfunction does not occur immediately, but changes slowly. The location of this fault should be on engine. The engine power output is insufficient, not chassis (such as slipping clutch), which loses engine power output, resulting in a situation where car does not move at high speed. speed and motor does not rotate at high speed.

To determine if a fault is a mechanical or circuit fault, service technician plugs in a V.A. G1551 and enters address code. 1. Check engine electronic control system: enter address code 02, check fault, fault counter shows sporadic faults, and fault content is: 17964, that is, boost pressure control is below control limit. Enter address code 08 to read data.

Group 002 is shown as:


Group 003 is shown as:


Group 033 is shown as:

16.5% 0.665V

The data is generally within standard range. Compared to a car of same type with same mileage, some individual data are clearly unstable, for example, speed 760-800 rpm, air quality. count 2.3-1.9g/s jumps back and forth from large to small mixture ratio density 16.5% oxygen sensor voltage 0.665V jumps very slowly, basically does not jump.

After reading, maintenance technician made a summary entry. Opened hood, did a thorough inspection of engine and found that engine was shaking a bit at idle and exhaust pipe glowing red abnormally. Intuitively, from above two phenomena, combustion in cylinder is poor, and residual mixture burns on three-way catalyst and exhaust manifold. The owner replied that spark plug had not been changed. Could it be that ignition of spark plug is bad, misfiring causes individual cylinders to be unstable, causing engine to shake, idle speed is unstable, gas mixture does not burn in cylinder, and this is three-way catalytic converter burned out, and exhaust pipe is abnormally red colors?

Maintenance case: Passat speed, increase in engine speed is not enough to troubleshoot

Immediately replaced spark plug of original car of same model, after starting problem remained. Then take an analysis of broken cylinder. When second cylinder is turned off, engine speed does not change significantly. There is a suspicion of a malfunction of ignition coil and misfires. Considering that if ignition coil is faulty, this can be determined by electronic engine control system, but no fault has been detected. Conduct repeated experiments to evaluate cylinder shutdown, and finally check that ignition coil of second cylinder is not working properly, replace ignition coil of second cylinder, engine does not shake, and idle speed is normal. By deciphering and analyzing content of random malfunctions, connections of intake and exhaust hoses of entire vehicle related to malfunctions were checked and found to be normal. After removing contents of fault, test drive, everything remained same. The content of error that was just removed has reappeared. All other data was normal, and attendants at this time fell into endless confusion.

From beginning, I returned to some doubts when reading data stream: why is air mass meter constantly jumping from high to low? And when charging, data first returns to 1.9g/s from 2.3~2.4g/s at fast speed, and then slowly increases? The output voltage of oxygen sensor is at a high level of 0.6 ~ 0.8V, and it rarely fluctuates?

After above comprehensive analysis, service technician concluded that failure was caused by a moderate blockage of three-way catalytic converter. When blockage of three-way catalytic converter is not very serious, when idle speed is empty and gas is filled, since engine has no load and chassis has no drag force, engine can hardly release exhaust gases slowly. relying on idle speed; when driving on a highway, engine chassis increases drag torque, so that at this time, in order to ensure high-speed and heavy-duty operation of engine, it is necessary to increase accelerator pedal. At this time, a large amount of exhaust gases emitted from engine cylinder cannot be sent out in time due to blockage of three-way catalytic converter, and high-temperature exhaust gas continues to increase in three-way catalytic converter. , causing exhaust pipe to become abnormally red. The oxygen sensor voltage is high and beating is slow, indicating a rich gas mixture. At same time, exhaust vane in turbocharger gas is blocked by a large amount of exhaust gases, and speed is reduced. With such a large load, boost pressure is low, so such a fault will be stored in ECU every time. time machine is tested! ByWith this idea, it was decided to dismantle three-way catalytic reactor, and it was found that small holes-channels of honeycomb catalytic chamber inside are all glued together into an integral sealing plane. After replacing new three-way catalytic reactor, trial run went well and problem was completely fixed.