Dayton Daily News

Q: My friend has a 2000 Jeep Cherokee. Several times the check engine light has turned on and remained on for several days, but for some reason it mysteriously turns off. Whether the light is on or off, the vehicle runs fine. Is this a critical situation? Will the computer reveal a trouble code for the problem? T.D., e-mail

A: Since you say the vehicle runs normally, illumination of the light probably is not the result of some critical problem. This could be the result of a lazy oxygen sensor, failure to shut off the engine when fueling the vehicle or even perhaps a dirty air filter.

To find the cause with certainty, there is a better chance to detect a fault when the light is on. However, the computer does have a memory that records and holds diagnostic trouble codes for a prolonged period, depending on the number of ignition key cycles and miles driven. Since this is the case, if the light should turn off just before a scheduled shop appointment, computer diagnostic codes, more than likely, will be held in memory for a technician to access.

Lowered tailgate poses safety hazard

Q: As a military pilot and aerospace engineer, I read with interest your answer to a question about fuel economy on a pickup truck with the tailgate up or down. I have read similar answers from other auto columnists.

My concern is with the tailgate down, it poses a safety hazard. If a vehicle hits the truck from the rear or the pickup is backing up, the tailgate extends beyond the bumper and can cause damage to other vehicles. Not only this, but if there is cargo in the bed, it might slide out. Also water collects in the tailgate. This can cause corrosion to the metal. Can you comment? L.T., e-mail

A: Many readers commented on my answer. Some mentioned a television program that analyzes myths. Readers who based their comments on a television show stated that fuel economy goes down when the tailgate is down. My answer was that I had not read any laboratory studies on whether fuel economy goes up or down with the position of the tailgate.

As a former military aviator, I, too, am familiar with aerodynamics, but you raise important safety concerns that pickup truck operators might consider. The tailgate can pose a safety hazard. If you are considering lowering the gate to experiment with fuel economy, you might also place a red flag on the gate or other devices to help make it more visible to you and other drivers.

Also, you might consider removing the gate altogether as sometimes when the gate is down and you hit a bump, the gate bounces. This can damage the sheet metal and trim. I’ve seen some so damaged they no longer latch to close.

Today’s oil better than long ago

Q: Many years ago, about the time multi-viscosity oil was first introduced, I took an auto mechanics class in night school. As part of the class, I learned about multi-viscosity oil. The instructor said that oil such as 10W-30 suffers molecular breakdown during extended use. Is this true? What is extended use? P.K., Huntington Beach, Calif.

A: Multi-viscosity oil has been around a long, long, time. Back when it was first introduced ,the recommended oil-change interval on most cars was every 1,000 miles. Motorists who lived in suburban areas and motored to work in urban central business districts such as New York, Los Angeles and Chicago were changing the oil and filter every month. This was because the additives in the oil that make it change viscosity break down.

The additive package in today’s multi-viscosity is better than it was 40 years ago. Also, engines are much better. Oil and filter change intervals have increased from 1,000 miles to 3,000 miles on vehicles driven in city traffic or suburban short trip travel.

 

Time And Mileage Lead to Failure

Q:My 1999 Chrysler 300M with 126,000 miles quit running. A mechanic diagnosed the trouble as failed cam and crankshaft sensors.

Is this caused by old age? What would cause both sensors to fail? Is the mechanic pulling my leg? B.H., e-mail

A:I see that you are in the military. I must thank you for your service to our country.

The failure is likely due to time and mileage. It is unusual for both sensors to fail at the same time, but I’ve been in this business a long time and anything is possible. Individual tests of the sensors would verify if both or one of the sensors failed. Once testing is completed you will know if the mechanic is giving you the run-around.

It is possible that both sensors share a wire harness. As a result both sensors might need replacement at the same time even only if one has failed.

It’s also possible that there is a fault in the wire harness to the sensors. There might be a loose connection, corrosion or a loose pin in a plug. If the sensors do not have a fault, probing the circuit related to the sensors is in order.

Cruising For Fire

Q:I just read your column about possible fires in Fords with cruise control. I need to know which vehicles are affected. I have a 2001 Ford F-250 truck. The cruise control works fine, but a couple of weeks ago a friend had her 2001 F-350 burn up in her driveway.

Do I have to take my truck to a dealership to have it fixed? R.M., e-mail

A: You must be referring to a defect in the cruise control deactivation switch. In some vehicles the switch can overheat and cause a fire even when the ignition switch is turned off. According to the information I have about 380,000 vehicles are affected ranging from model years 1994 to 2002. I don’t think your vehicle is affected, but a Ford dealership would have updated information that could include your truck.

If your vehicle is affected by the recall you should have received a notice in the mail. If not, it’s not likely your vehicle has been recalled.

Call your favorite dealership to find out for sure. A service department representative can determine if your vehicle is affected by the recall. He or she will need the year, model and vehicle identification number.

If your truck needs attention, take it to a dealer to have the cruise control disconnected. This is a temporary measure to prevent a possible fire just in case the dealer parts department doesn’t have the updated parts to solve the trouble.

Vehicle Storage Stirs Debate

Q:I have a Corvette that I store every winter. I have received two different opinions as to the proper way to store the car. One opinion is to add a fuel stabilizer to the gas tank then drain it as low as possible and remove the battery to minimize the risk of a fire. The other opinion is to fill the gas tank, add a fuel stabilizer and place a trickle charger on the battery.

What do you suggest? B.D., Woodbury, Minn.

A:This will give you more to consider. You might know the old saying if you don’t use it you lose it. Fill the gas tank, make sure there is a fresh supply of oil in the engine, disconnect the battery cables and place a trickle charger on it. About once a month on a nice dry winter day make sure the tires have proper inflation, connect the battery and take the car for a drive of about 10 miles. A 10-mile drive should bring the engine to full operating temperature to remove moisture and other contamination in the drivetrain.

Enjoy the ride, the seals in the drivetrain will remain lubricated to help prevent future leaks and the brakes won’t suffer from corrosion damage. On top of all of this the likelihood of the engine suffering from fuel system ailments will be greatly reduced.

Smoke Can Find A Leak

Q: The check engine light is on in my 1998 Ford Ranger with 47,000 miles. I checked for trouble codes and found codes PO171 and PO174. These codes indicate a lean running condition. I erase the codes but it isn’t long before the check engine light turns on again.

I checked the air filter, fuel filter, fuel pressure regulator, fuel injectors and fuel pump. They check out fine.

Also, the mass airflow sensor appears to be very clean and unobstructed. All sensor connections are clean and sound. All hoses and tubing are firmly connected and sound. I’ve narrowed down the cause to a vacuum leak or air leak.

What is the best way to search for a vacuum leak? Should I probe using Freon or Propane? Will the computer mask these methods? Or, should I use a stethoscope? D.F., Hampshire, ILL.

A:You are on track to replacing the plenum gaskets and seals. Also, the exhaust manifolds could have a leak. Let’s apply the brakes before you do unnecessary work. Before you dive into this project any further you could use throttle body cleaner to check for leaks, but the best method is smoke. Technicians often use a smoke machine to detect vacuum and air leaks at the exhaust manifolds, intake plenum, vacuum lines and fuel evaporative system. Since it’s likely you don’t own a diagnostic smoke machine you may find a leak using throttle body cleaner. However, your description of the trouble appears to be derived by a malfunctioning mass airflow sensor. You might consider cleaning the unit even though it appears clean. If the symptoms don’t cease further testing of the unit should verify a malfunction. If so, replacement should be the cure.

Also, it’s possible carbon deposits in the engine are causing conditions that appear to trigger the computer to run the engine lean. Consider adding a carbon cleaner additive to the fuel tank. This might resolve the condition.

Lack Of Fuel Impairs Engine Starts

Q:Three years ago I purchased my 1995 GMC. It now has 164,000 miles on it. It has a 4.3 liter V-6 engine that is not the factory original. It has been running great until recently. For the past 30 days the engine is difficult to start. The battery is good and the starter cranks without trouble. The trouble is the engine just won’t start.

To start the engine I give it a shot of starting fluid. One squirt is all it takes. Once the engine is running I can shut it off and it will start fine the remainder of the day.

Since the engine is not the original I can’t follow self-diagnostic test procedures. As I’m a do-it-yourselfer I tested individual sensors according to repair manual procedures. They all check fine. I also replaced the fuel filter and spark plugs, but this didn’t solve the trouble.

It appears that there isn’t any fuel to the injectors. Could this be a powertrain control module problem? D.M., Virginia Beach, Va.

A:You have been thorough in your quest to find the trouble and repair it. Don’t give up you will find the cause of the condition. You are on the right track. A lack of fuel is likely.

Check the fuel pressure. The 4.3-liter engine fuel pressure regulator and hoses have a tendency to develop leaks. Sometimes leaks become so prevalent that fuel contaminates the engine oil.

Sniff the engine oil. Your nose might detect gasoline. If so check for fuel pressure regulator leaks. You’ll find test procedures in your repair manual. If this is the cause replacing the regulator is the cure. Also, change the engine oil and filter so engine bearings aren’t damaged due to gasoline contaminated oil.

Technician Follows Diagnostic Equipment Prompts

Q: There is a nagging starting problem in my 2000 Oldsmobile Intrigue with 56,000 miles. For the past three years occasionally the engine is difficult to start. When this occurs I turn the ignition key, the engine cranks and wants to start, but it doesn’t. Then I shut off the key and try again. Usually on the second try it starts right up but there have been times when I have to go through the routine 15 times before the engine starts. By then there is a strong gasoline odor. When the engine does start it runs fine. This trouble occurs once or twice a week. Other than this issue the car is fine and drives as it did when it was new.

Given that this is an intermittent problem I fear that if I take the car to a mechanic I will end up paying for his education. However, I don’t like being stranded either. What’s your advice? G.N., Dayton, Ohio.

A: Trade it in. Of course I’m just kidding. Your car can be fixed. This might simply be caused by a dirty mass airflow sensor or throttle body. A thorough cleaning might do the trick.

Take the car to an experienced A.S.E.-certified technician. He will scan the computer for trouble codes. This likely will lead him to the source of the trouble.

The self-diagnostic capabilities of your car are very sophisticated. The test equipment used by an experienced technician also is very sophisticated. The diagnostic tool basically communicates with the car’s computer, performs a series of tests that checks sensors and the computer for variances from factory specifications. The equipment prompts a technician through the procedure and tells him where to look for the cause of the trouble.

Sensors such as the mass air flow sensor measure air temperature, barometric pressure, air volume and more. Dirt impairs proper function. If tests find the airflow sensor is not up to par cleaning might revive the part.

It’s also possible that this is caused by a faulty throttle position sensor, crankshaft sensor, camshaft sensor or oxygen sensor. If this is true, tests will verify a fault. Replacement will end your woes.

 

Phil Arendt is an automotive columnist, consultant and

ASE-certified master technician.

E-mail him on the Web at

http://www.drgizmo.ws.