Symptoms: A 2008 Porsche Cayenne (Cayenne) sedan, equipped with a M5501 V6 engine and a mileage of 20,000 km, has been reported to be unstable by users when the car is cold. Especially in the winter, after the cold car started in the morning, the engine jitter was very obvious. After 30 seconds, the shaking phenomenon disappeared.
Inspection and analysis: Because the fault phenomenon is related to temperature, the coolant temperature and intake air temperature sensor signals are first checked as usual, and the measured values ​​are consistent with the ambient temperature. Check the air intake system and found no obvious leakage. The engine control unit was tested without a fault code, but one cylinder or multiple cylinders were found to be misfiring when reading actual values. Then the throttle was cleaned and the ignition system was checked. No abnormalities were found. The cylinder pressure and leak rate were measured and were all in the normal range. After finishing the diagnostics, the focus of the inspection was on the fuel system. This car uses direct fuel injection technology, a total of three fuel pumps, respectively, two low-pressure fuel pumps and a high-pressure fuel pump. Using a fuel Pressure Gauge to measure the low pressure fuel system, the engine can reach 0.55 MPa when running, which is a normal value. After the vehicle is turned off, the fuel pressure can be kept within the normal range. Read the actual value of the fuel high pressure measured in the engine control unit and found that under different operating conditions of the engine, the high pressure fuel pressure changes within 4-12 MPa, which is normal. Using the endoscope to inspect the injector, no leakage was found, but it was found that the coke deposition in the cylinder was obvious, so the fault was judged to be caused by too much coke.
Troubleshooting: After removing the carbon deposit in the cylinder, the fault disappears completely. After a period of time for a return visit, the user reported that everything was normal.
Reviewing and summing up: This engine adopts the direct injection technology in the cylinder. The control unit strictly controls the fuel injection quantity. Due to the large amount of carbon deposit in the cylinder, some of the injected fuel cannot be mixed with the air, causing engine misfire. At present, Porsche has advised users to use Porsche-specified fuel additives to solve such problems.
What is MMA welding?
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Manual Metal Arc welding, often known as Shielded Metal Arc Welding (SMAW), stick welding or just arc welding, is a welding process where a coated consumable electrode (or stick) is used to lay the weld.
An electric current produced by the welding power supply is used to create an arc between the electrode and the metal to be welded. The arc melts the core of the electrode to produce drops of molten metal to create the weld. The flux coating of the electrode also melts and produces a shielding gas and provides a layer of slag which protects the weld from any contamination in the atmosphere. The slag layer needs to be removed after each weld.
What are the benefits of MMA welding?
Cost – MMA Welding Machines are relatively low cost and the operating costs are also lower than with other welding techniques.
Mobility – MMA welding machines are compact and lightweight making them easily portable and ideal for use anywhere.
Simplicity – the equipment is relatively easy to operate and the procedure is simpler than some other welding processes.
Flexibility & versatility – whilst MMA welding is used primarily for welding steel (including stainless steel) and iron, it can also be used for a wide variety of other metals including aluminium, nickel and copper alloys. It is also the most effective process for welding outdoors as it less likely to be affected by weather conditions than MIG or TIG welding.
What are the disadvantages of MMA welding?
Quality – MMA welding often produces quality issues which can affect either the strength or the appearance of the weld or both. The most common problems are weld spatter, porosity, poor fusion, shallow penetration and cracking.
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