2012年8月12日星期日

INJECTOR PROBLEMS

Diesel injectors can suffer from the same kinds of ailments as gasoline injectors, including varnish deposits, clogging, wear and leakage. Today’s low sulfur diesel fuels are more likely to leave varnish and gum deposits on injectors, and also provide less lubrication so you might try an additive to keep things flowing smoothly.

Diesel injectors operate at much higher pressures than gasoline injectors. Over time, their opening pressure can drop. Up to 300 psi is considered acceptable but more than 300 psi means the injectors should be replaced or reset back to their original operating specs. You’ll need some type of pop tester to check the opening pressure of the injectors if you suspect this kind of problem. Dirty injectors will lean out the air/fuel mixture, causing a loss of power, rough idle and sometimes white smoke in the exhaust. Leaky injectors will richen the air/fuel mixture and cause black smoke.

There are a couple of ways to find a bad injector on a diesel engine. One is to use a digital pyrometer to check the operating temperature of each cylinder. A temperature reading that’s lower than the rest would indicate a weak cylinder. If compression is okay, the problem is restricted fuel delivery. Another quick check is to use an ohmmeter that reads tenths of ohms to measure the resistance of the glow plugs while the engine is running. The resistance of the plug goes up with temperature, so if one or two cylinders read low, you’ve found the problem. For example, if a glow plug normally reads 1.8 to 3.4 ohms on a hot, running engine, a reading of 1.2 to 1.3 ohms on a glow plug would tell you that cylinder isn’t producing any heat.

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