Northwest Herald Dr. Gizmo column dated October19, 2012

10/19/2012

"Dr. Gizmo"

By Phil Arendt
 

Engine Idles Rough Due To Lean Fuel Mixture

Question 1

The 3.0-liter engine in my 2001 Mazda Tribute runs fine until it warms up.  Once it is warm it idles rough.  Sometimes it stalls.  When it stalls it starts back up and runs fine for a short time but then it begins to run rough again. 

I took the car to my local shop where a mechanic did all kinds of tests.  He found trouble codes for misfires and others for lean fuel.  He tested the sensor on the crankshaft, timing and fuel pump but everything seems fine.  Since the engine was misfiring for him he replaced the spark plugs and sensor on the crankshaft.  With this work the engine runs better but not as good as it did before the trouble started.

Do you have any suggestions? H.B., email

Answer 1

It appears that your technician did not address the reason for lean fuel trims.  Trouble such as this could be caused by air leaks such as a cracked vacuum line or even a failing fuel pump or pressure regulator. 

Ask your technician to consider checking for these possible causes the next time you visit his shop.

Transmission Flush Long Overdue

Question 2
When coming to a stop in my 2007 Audi A3 sometimes the engine speeds up a little and the transmission downshifts.  The same thing happened several months ago.  At that time I took the car to a dealership where they replaced hoses, throttle body and a valve.  After the work the trouble was fixed. 

This time I took the car to a local shop where tests did not find any trouble.  Since the car has 54,000 miles the mechanic suggested cleaning the throttle body.  This procedure did not cure the trouble.  Now he thinks the problem might be cured by flushing the transmission.  I have never had this done.  Also, I have never had it done in any car I have owned in the past.  Does this make any sense to you?  D.N., email

Answer 2
The automatic transmission in your car has a dual clutch system and should be serviced according to the manufacturer’s service schedule about every 15,000 miles.  I’m not sure what you and your technician experience when slowing to a stop but perhaps the transmission downshifts a little too soon as you slow down.  Flushing the transmission might cure this problem and even if it doesn’t the service is long overdue.

If the transmission flush does not cure the trouble it’s possible the engine or transmission control modules need reprogramming.  Ask your technician to consider these suggestions when you take the car back to his shop.

Time To Replace The Air Conditioner Compressor

Question 3

I have a 2007 Honda CR-V with an air conditioner that does not work.  I checked the fuses and they are fine.  When I turn on the air conditioner I can see that the compressor is not turning on.  I took the car to my repair shop that has been servicing our family cars for many years.  Until now I have always trusted their diagnosis.  They have been right every time.  This time I’m not so sure.

 A mechanic did some tests on the A/C system.  He has checked relays, wiring and control module.  He has cycled the compressor with his equipment and it turns on but he says the compressor needs replacement.  If it works, why does it need replacement?  B.P., email

Answer 3
I understand how you might consider the diagnosis fishy.  The compressor and clutch is a unit.  Within the unit is a thermal protection circuit.  When the mechanical load of the compressor becomes too great due to internal failure the electrical portion overheats.  When this happens the thermal protection built into the unit turns off the compressor.  This protects the remainder of the circuit from an electrical overload that could otherwise cause failures in other parts such as the dash control module, relays or wiring.

It appears your technician has properly diagnosed the trouble.  It is time to replace the compressor. 

Shortcut Saves Time

Question 4
The timing belt in my 2003 Volkswagen Jetta with 197,000 miles and a diesel engine jumped.  I had the car towed to a repair shop where a mechanic determined the trouble.  He quoted a price for the repair which also includes removing the sub-frame on the engine.  He said this is necessary to get to the belt.  This is a big expensive repair job.  Is this really necessary?  N.W., email

Answer 4

Our repair manual does indeed state that the sub-frame needs removal.  However, after visiting a couple of professional websites some technicians have found that it is not necessary as they have found a shortcut.  They are able to gain access to the items that are necessary to remove the belt by loosening the sub-frame just enough to provide the necessary room.  Regardless, it is still a task that is labor intensive to complete.

Labor time charged by a technician is based upon an industry standard labor guide.  When the guide is produced the published repair time is based upon studies usually of three repairs for the same problem or task with all the tools and equipment on the ready to complete the job.  A technician does the task under controlled conditions and is timed.  The average time is published in the labor guide.  On newer cars the time to complete a task is less than the time it takes to do the same repair on an older vehicle.  The industry standard labor guide gives more time on older vehicles because rusted and corroded fasteners are more difficult to remove than the fasteners on new vehicles.  In some cases the published time to repair a new car is half the time it takes to repair an older vehicle for the same task. 

A technician might be able to complete a task within the time allotted in the labor guide.  If he does he stands to make more money because he can complete more tasks in a day.  However, if a bolt breaks and he has to do additional work and completes the job over and above the labor guide time he completes fewer jobs in a day and does not make as much money or could even lose money.

New Pump Should Cure Power Steering Trouble
Question 5
Sometimes the power steering in my 2006 Mercedes-Benz ML500 with 126,000 miles becomes very stiff.   Also, the check engine light is on.  I took the car to an area shop that specializes in Mercedes repairs.  The mechanic connected a diagnostic tool to the car and found so many malfunction codes he does not know where to start.  He said it would take a while to trace all the codes.  Three days later he called to inform me that the power steering pump needs replacement.  He said he connected a pressure gauge to the pump and drove the car.   When the steering stiffened the pressure was low.

This is not the first shop to work on the car.  I have taken it to three different shops for power steering problems.  One shop replaced the steering gear.  Another shop replaced the pump.  The other shop replaced some lines and front wheel sensors.  When I told this mechanic the pump had been replaced he said it looks like an aftermarket pump.  He said he will install a pump from the Mercedes factory.  He says he is confident this will fix the trouble.  Do you agree?  D.C., email

Answer 5
Yes.  What he suggests should cure the trouble.  However, before authorizing the repair come to an agreement that if his work does not cure the trouble he will take the factory pump off, reinstall the aftermarket pump and not charge for the work.  Be sure to get it written form.  

Battery Not Faulty Circuit Is Cause Of Trouble

Question 6
The battery in my 2007 Ford Explorer with 24,000 miles goes dead after two days of not using the vehicle.  I took it to a repair shop where a mechanic found a draw of about 40 milliamps that goes away after about 15 minutes.  He says the draw kills the battery.  He checked the circuit that is causing the draw for faulty equipment.  After two days of testing he can’t find anything wrong.  Now he is at a loss.

Do you have any suggestions?  N.L., email

Answer 6
Sure, drive to the nearest McHenry County gravel pit.  Ask an operator of a huge front-end loader to run over your Explorer.  That should cure the trouble.

All kidding aside, the next step is to charge the battery and load test it.  More than likely, it will fail testing.

A parasitic draw of 40 milliamps on a battery could be normal based upon battery capacity.  It takes time for all the computer modules in your vehicle to go to sleep.  Apparently, in your vehicle it takes 15 minutes after the ignition is shut off for modules to shut down.  During this period they continue to draw power from the battery.  This is not unusual.  If the battery fails due to this minor draw, more than likely it has an internal fault that only replacement will cure.

Testing will verify if this theory is true.  If so, a new battery should cure the trouble.

Thanks for all of your great questions.  Dr. Gizmo can’t wait to answer more.
Phil Arendt is a columnist, consultant and A.S.E.-Certified Master Technician.  Readers may send questions to Dr. Gizmo at P.O. Box 548, Cary, IL. 60013 or e-mail address drgizmo@drgizmo.ws. 10/19/2012 ® DR. GIZMO © 1989-2012