Mercedes 126 Repair - Tracking Down Vacuum Leaks

Mercedes has always had a tendency to use multiple vacuum as a control device for a variety of auxiliary systems. As elegant as it May be, it does result in engines with lots of vacuum lines and connections at the top of the already complicated fuel injection and air management system. If this is the myriad of components has never been restored to 20-year-old car, it will almost certainly be a leak, and they can be tricky to track down.

vacuum leak symptoms

Major vacuum leak the engine will be very rough or lumpy at idle as the optimal air / fuel (/ F) ratio is an endangered listing unmetered air. car can still drive reasonably well, because the relative size of leakage becomes much less significant because it opens the throttle and the engine draws in large volumes of air required for combustion under load. Idling speed can be increased, as a vacuum leak frustrates efforts to idle control system to regulate the amount of air admitted to entering port.

economy gauge in the instrument should be pegged to the left idle (unless the gear with A / C on). But that's not enough to accurately measure the correct diagnosis. We really want to connect handheld pressure gauge on the intake manifold. The best place for it on the back of the manifold on the passenger side, where the gray lines the interior takes its food supplies. healthy engine is idling, according to most textbooks, should be included in the 17-22 / Hg of vacuum, in the case of V-8 Mercedes 126, we should see about 20 a smaller number may indicate many things, including improper ignition timing, and generally poor condition of the engine. But if the engine is otherwise sound, a vacuum leak will be visible here.

The best method of detection

One way to find the vacuum leak is the automotive stethoscope. You May be able to actually hear taking a false air. But the best way is to use your car Senor oxygen as a diagnostic aid. oxygen sensor in the early V-8's is a wire device, sends a voltage close to 1.0 when / F ratio is rich and close to 0.0 when the mixture is very lean. Combining the sensor output wire through the voltmeter to the battery ground, it can be used for testing the vacuum leak. To do this:

Get HOT sensor from driving cars. Test sensors lean response by creating a massive vacuum leak. Disconnect the gray lines on the back of the branch, where he linked up his pressure gauge. Test sensors rich response spraying carb cleaner in intake. (air cleaner should be off for this job.) If the sensor does not respond properly, replace it. It is essential for the proper mixture control and fuel economy. If the sensor is working, test for vacuum leaks by spraying a small amount of carb cleaner around the suspected areas of leakage, such as fuel injector seals and air hoses. If you see a short class in power, you've found the problem. Do not go crazy carb cleaner: it is hostile to the old tires.

Unfortunately, not all of the possible culprits could be achieved with this procedure. rubber "donuts" between the upper and lower half of the intake manifold is almost impossible to test. But typically, some combination of this procedure plus temporarily isolating the vacuum-powered equipment will expose the leak.

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