Dayton Daily News

Examine the carburetor immediately after turning off the engine. The fuel pressure will cause a faulty carburetor to leak.

Until this trouble is solved, do not drive the vehicle. From what you describe, gasoline is contaminating the engine oil. This will impair the ability of the oil to lubricate bearings and moving parts within the engine. This could result in severe damage that could ruin the engine.

Once the condition is repaired, change the oil and filter immediately and two more times within 1,000 miles of the repair. This will remove any residual gasoline in the oil and inside the engine block.

Slick fix for power windows

Q: The power windows in my four-door 1992 Chevrolet Blazer only run part-way down and then quit. If I let them sit for about five minutes, when I move the switch to lower them, they will move a little more.

I replaced the circuit breaker for the system, but the windows continue to quit part-way up or down. I suspect the motors have failed, but it’s hard for me to believe that all four window

A: The system in your vehicle is fairly straightforward. There is one
30-amp circuit breaker providing electrical power, the driver’s door control, switches for the windows in the other three doors, a motor in each door and wiring connecting everything together to power from the breaker and a ground connection in the left side of the dash.

It’s not likely that all four window motors failed at the same time. Consider applying a liberal amount of automotive silicone spray lubricant to the window channels that guide each door glass. You might need to purchase a couple of cans of lubricant to do a proper job. Lower a window at a time. As the glass lowers, apply the spray lubricant to the channels at the front and rear edge of the glass. The lube job may return normal operation.

Also, make sure that the ground connection in the left side of the dash is free of corrosion and secure. Check all the connections at the switches, too. Fix if needed.

If these attempts don’t cure the trouble, it’s possible each motor has weakened as a result of time and mileage. If so, replace the motors.

Minor collision causes total failure

A: Vehicles are complex pieces of machinery. Also, quarters are cramped, so there isn’t a lot of space for the electronics and drivetrain. As a result, even a low-speed collision reverberates through the entire car with a jolt. This can jar a connection loose.

Maybe the battery jumped a bit. In doing so, it’s possible the positive cable hit sheet metal and caused a momentary short circuit. If so, it’s possible a circuit breaker opened or perhaps a sudden change in polarity caused the engine control module to fail.

Once a technician probes for the trouble, it shouldn’t be too long before the cause of this condition is found. A lasting cure should follow.

Misdiagnosis A Possibility

Carburetor leak fouls engine oil

A: It’s possible, but unlikely as installation of a new fuel pump did not cure the trouble.

More than likely, the trouble is caused by a faulty carburetor. The carburetor may be leaking fuel from the fuel bowl into the engine block. A visual inspection of the throat of the carburetor may find fuel dripping into the engine. If so, an overhaul of the carburetor or installation of a remanufactured carburetor should cure the problem.

Examine the carburetor immediately after turning off the engine. The fuel pressure will cause a faulty carburetor to leak.

Until this trouble is solved, do not drive the vehicle. From what you describe, gasoline is contaminating the engine oil. This will impair the ability of the oil to lubricate bearings and moving parts within the engine. This could result in severe damage that could ruin the engine.

Once the condition is repaired, change the oil and filter immediately after the repair and two more times within 1,000 miles of the repair. This will remove any residual gasoline in the oil and inside the engine block.

Misdiagnosis A Possibility

Q: My girl friend owns a 2000 Chevrolet 4X4 Silverado pickup truck. She hears a hum sound that seems to come from the rear of the truck when slowing from 50 mph. The tires have been rotated and balanced. There aren’t any loose shields on the exhaust. The spare tire is tight and all the driveline u-joints appear fine. Dealer personnel tell her that the source of the noise is a worn u-joint.

I did some research at the library and found some information that the noise might be caused by the transmission. However, dealer personnel tell her the transmission is fine.

A: Dealer personnel have the latest technical information, tools and expertise to diagnose just about every problem that can occur. If a technician has a problem that he is having difficulty in pinpointing he can tap the vast information and technology that General Motors provides to dealerships. Much of this information is private and only accessible to their dealer body. If a technician has determined that the noise is caused by a failing universal joint in the drive shaft it is more than likely the cause of the humming sound. Replacement is the cure.

It is however possible that the trouble has been misdiagnosed. Your girl friend might consider taking the truck to another repair shop where a technician might consider that the sound is caused by wear patterns in the tires. If so replacing the tires might end the concern.

It’s also possible the cooling system fan or driveshaft has a fault. In addition to these suggestions perhaps the driveshaft slip joint needs lubrication or if it excessively worn, replacement.

Failed Oxygen Sensor Needs Replacement

Q: Recently the check engine light illuminated in my 2003 Chevrolet Venture with 48,000 miles. I took the vehicle to my dealer where I received a report that stated that it looks like the oxygen sensor is failing. Dealer personnel offered to replace the part for $196. When I asked if the replacement would cure the trouble I was told “maybe”. I thought that for $196 the cure would be guaranteed.

A: There are three levels of failure that turn on the check engine light. Depending upon the severity of the condition that caused the computer to turn on the light determines the level of failure. When the light illuminates a failure code is stored in the computer. A technician’s diagnostic tool reads the code. The code tells him or her which circuit or part has failed.

In your case the code was related to the oxygen sensor. The circuit might have a fault. The sensor may have failed or the heated portion of the sensor might have failed.

Testing the circuits might find a loose connection, corrosion or a fault in a plug such as a loose pin. Tests of the sensor may find that it does not respond quickly enough or the voltage it produces is out of factory specifications. With the information at hand a technician decides the best course of action. He can repair a circuit or replace the sensor if needed. Apparently in your van the best action is to replace the sensor.

There might be other problems. If there is a condition within the engine such as an internal coolant leak, dirty throttle body, aftermarket fuel additives, leaky fuel injectors, contaminated gasoline, poor gasoline formula, vacuum leaks or other conditions that are causing the oxygen sensor to run amuck installation of a new sensor may not cure the condition. Hopefully this isn’t the case and a new sensor will end your concerns. Having said all of this from what you describe a new sensor should do the trick.

Thanks for all of your great questions. Dr. Gizmo looks forward to more.

Phil Arendt is an automotive columnist, consultant and

ASE-certified master technician.

E-mail him on the Web at http://www.drgizmo.ws.