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Santana failure Jitter idling the engine 1 case 3000CNG

Failure phenomenon: a 2009 annual Shanghai Volkswagen 3000CNG taxi, mileage 34000 km. The car user is reflected in the gas operation mode (using natural gas as fuel) of the engine idle shake, weak acceleration, while in normal operation when the gasoline operation mode.

Check Analysis: I first trial run, after starting the engine, the operating mode changeover switch (gasoline, gas operation mode converter) is adjusted to the gas operation mode. When the engine using natural gas as fuel operating, the engine jitter was found that the fault is determined as the user.

Next, the author uses VAS5051B fault diagnostic system for engine control diagnostics. First of all, prevent memory, found no fault memory. Then, check the data writer engine control system, click ldquo; Read data block rdquo ;, and input channel number 003, data flows in this group was observed. From the data set 003, we can see the throttle angle is slightly larger, but not enough to cause failure phenomenon of the car. I also enter the 014 sets of data, check fire conditions, we found that the total number of fire as ldquo; 11rdquo ;, we can see the engine misfire phenomenon has appeared many times. In order to determine in which cylinder misfire occurs, I see the 015 and 016 sets of data flow, data show that the number 2 cylinder misfire is ldquo; ;, several other fire 6rdquo each cylinder are ldquo; 0rdquo ;, indicating that the cause of the engine shake 2 is a cylinder misfire. When the misfire phenomenon described 0rdquo ;, whereby only the use of natural gas fuel;

I switch the operating mode to the gasoline operation mode is adjusted, and then observed for several fire group 015, the number of the cylinders are misfiring becomes ldquo It appears, so you can rule out the possibility that the fuel injection system leads to failure. It seems the cause of this failure should be the gas system or the ignition system.

first check the ignition system. As the car’s mileage has reached the replacement cycle spark plug (30,000 km), the author suspected spark plug misfires lead to a fire phenomenon, so the replacement of all the spark plugs, and then check the number 2 cylinder misfire again, the result of fire still exists. The engine is the use of a common two-cylinder ignition coil design, the cylinder 2 and the cylinder 3 share a pointIgnition coils. So I 3 and the cylinder 2 of the high-pressure cylinder ignition wire exchange, and then checks the number of fire, the fire is still 2 cylinder, thereby eliminating the possibility of failure of the ignition coil and the high voltage ignition wire.

Next, check the gas system. The author cylinder 1 and cylinder 2 jet nozzle exchange, the fault persists, ruled out the possibility of the jet nozzle failure; removing jet pipe examination, did not find a leak or clogging. At this point the work of the diagnosis had reached an impasse, surprisingly, when I will raise the engine speed to 2 000 r / min and maintained, then check the fire, and found fire disappears, which makes diagnosis thinking I clear up again. Probably due to the excessive intake throttle too dirty and coke, an intake manifold leading to smaller diameter, the intake air amount also decreased, resulting in insufficient gas mixture into the cylinders during idling, leading to engine shake. When the engine reaches 2 000 r / min, since the throttle opening is increased, the intake air amount increases, the engine rotation speed increase also increases the acceleration of the intake air into the cylinder such that the gas mixture increased, improving the combustion in the cylinder situation.

Troubleshooting: In order to verify this point of view, the author of the throttle and washable inlet, and completely remove coke, retest the car wash is finished loading, fire disappears, the engine shake disappears.

reviewed: Why can result when too much coke burn natural gas engine shake, while burning gasoline normal? My analysis, the impact of gasoline and coke for both fuels natural gas is different. When using gasoline as a fuel influence, too much coke will absorb a portion of the injected fuel, which can lead to difficulties in engine cold start, when hot car, absorption is no longer saturated coke fuel, the engine will not produce . When using natural gas as a fuel, since the jet nozzle far from the injector with respect to the intake valve, too much coke will hinder the gas mixture into the cylinder, resulting in insufficient mixed gas, this effect is sustained, thus causing the engine shake when the speed increases, the intake air amount due to an increase of the situation improved.

(Caoshou Jun)

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