por 2tracing Dom 30 Ene 2011, 20:27
Ale,ya que andás con el mismo problema...esto(mas abajo) tal vez sea de utilidad.
Desde el PCV que no es mas que la valvulita que va desde la tapa de válvulas al múltiple.(retorno de gases del carter) Voy a empezar con esa prueba...
Lo q no pude encontrar a simple vista. El tanque de nafta tiene retorno de gases a la admisión?
Rich O2, Narrow Pulse And Rich Exhaust Gases
When an O2 sensor reads rich, the injector or mixture control (MC) solenoid (on feedback carburetors) has a narrow pulse and the exhaust is rich, what are the possible causes? Probably the most common problem here is oil contaminated with fuel. This is usually the result of an underlying problem such as a misfire, a defective positive crankcase ventilation (PCV) system, a dead O2 sensor, a bad coolant sensor, or any condition that causes the engine to run rich. It drives me crazy to see how many techs overlook this obvious problem.
First, fuel contamination should have been identified during the initial inspection by sniffing the oil. Second, this is easily tested for with an infrared (gas analyzer). Pulling the PCV when running should not drop the CO by more than 1 percent on a properly functioning system. Third, and probably most important, any engine that has failed emissions probably needs the oil changed! If an engine has been running improperly, fuel will make its way into the crankcase. Do yourself and your customer a favor and change the oil. Sure, you may want to let the PCV system pull the fuel out now that the system is fixed. Just remember that the learned mixture values in the computer will have to constantly change to update, and the car may not run well until these values stabilize. And while rare, a crankcase explosion is possible.
PCV systems also can create a rich condition. Remember that the PCV system is a controlled vacuum leak. The PCV system has to carry oil, water and combustion gases out of the crankcase into the intake manifold for reburning. The components that the PCV is expected to evacuate are also the building blocks for sludge. The PCV system is very prone to plugging from this sludge. Make it a habit to service this system on every car in for a tuneup or emissions, or a driveability complaint. You can run a quick check of the PCV system by installing a vacuum gauge on the dipstick tube. How hard is that?
Fuel evaporative emission systems are another simple reason many engines run rich. This is another one that drives me nuts. Don’t make your job any harder than it already is! Eliminate the easy stuff first. Many of these systems suffered from high failure rates at higher mileage. Diagnosis is simple, just disconnect the evaporative hoses and see if the rich condition improves. How many techs are checking the air filter on the bottom of GM canisters? How many techs are checking the older canister vacuum diaphragms? Some canisters are full of fuel from customers over fueling the tank or parking facing down on a steep slope. Be sure to check for this and educate customers to prevent future problems.
High fuel pressure and vacuum-controlled fuel pressure regulators with leaking diaphragms can also cause a rich condition. The leaking diaphragm should have been found in the early inspection phase of diagnosis. When to test fuel pressure is more of a judgment call. This is largely dependent on how hard it is to test. A system with a schrader valve on the rail should be tested right away, but with a TBI unit that takes a half an hour to test, you may want to eliminate some easier possibilities first. The tip off to high fuel pressure and leaking diaphragms is usually an incredibly short injector on-time.
Leaking injectors also have a similar effect, except they usually will not affect all cylinders. A cylinder balance test, along with recording the changes for all four exhaust gases, will usually pinpoint leaking injectors. Also running the cylinder balance test at idle and 2500 RPM will help pinpoint this type of problem. The injectors will usually clear up at 2500 RPM because the amount of fuel needed exceeds the leakage. This test is also helpful in diagnosing vacuum leaks as they become less influential at higher air flow. Leaking injectors can be tested with pressure drop testing after confirming that the system drops are not the result of a leaking fuel pressure regulator or the often overlooked check valve in the fuel pump on the delivery side. If rubber lines are available, they can be clamped off to eliminate these problems. At my shop, we had hoped to test for leaking injectors by shutting off the engine and trying to start with the throttle floored (clear flood mode). The clear flood mode is entered when the computer sees wide open throttle (WOT) and less than 400 RPM. We have often been told no fuel is injected in clear flood mode. This is not always true, many manufacturers go to a 20:1 fuel ratio and the car may start. Also, residual fuel in the intake or crankcase may cause the car to start. We have not found this test to be a reliable indicator of injector leakage.
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