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Friday, May 11, 2012

Northwest Herald Dr. Gizmo Column Dated Friday, May 4, 2012


05/04/2012

"Dr. Gizmo"
By Phil Arendt

Leaking Valves Cause Misfire
Question 1
The check engine light is on in my 2001 Isuzu Rodeo.  I took the vehicle to a dealership where a technician found cylinders one and three were misfiring.  He replaced the spark plugs but this did not cure the trouble.  Now he says that cylinders one and three are misfiring because of leaking valves.  He says to fix it the cylinder heads need an overhaul.  I have owned many cars in my life but never had one that developed leaky valves.

My Rodeo has a 3.2-liter engine and 91,000 miles.  I have changed the oil and filter every 3,000 miles.  The truck looks as good as new.  It has never given me trouble until now. 

Grinding the valves is a major expense.  Is there anything else that might cause them to leak? P.T., email

Answer 1
At 88,000 miles it is premature for valves to suffer from excessive wear, but such a condition can develop even at this mileage.  Despite this, broken or weak valve springs can cause leaky valves.  Heavy carbon deposits on the valves can cause leaks, too.  Sometimes a leaky intake plenum gasket or sticky exhaust gas recirculation valve cause cylinder leakage that can be interpreted as leaky valves.  These issues can often be resolved without major repair work.

Ask shop management to consider checking for these conditions before authorizing removal of the heads.

Rough Idle Continues After Major Repairs
Question 2
The 3.0-liter engine idles rough in my 2002 Ford Taurus.  I took it to a shop where a technician found exhaust gasses in the cooling system.  He replaced the cylinder head gaskets, spark plugs and wires.  He also replaced the exhaust gas valve.  Despite all of this work the engine continues to idle rough.  He has run all kinds of tests but can’t find the cause.

My car has 88,000 miles and runs fine except for the rough idle.  The check engine light has never turned on while driving.  My technician says if there is a problem it should turn on but says sometimes when there is a minor problem it will not.  Now he is at a loss.

This shop has been working on our family cars for many years.  I trust this crew of experienced technicians.  The manager says he will put another man on the car and perhaps this will help find the cause of the rough idle.  Can you help?  L.M., email

Answer 2
Your technician has done a lot of work.  I’m sure he is just as frustrated by this condition as you. 

A rough idle can be caused by heavy carbon deposits.  If this is true, chemical treatment might cure the condition.

Additionally, since a cylinder head gasket failed perhaps engine coolant has been leaking into the exhaust system.  One of the oxygen sensors might not be responding as quickly as it should due to coolant contamination.  Tests of the oxygen sensor response times, voltage and fuel trims might find a sensor needs replacement.

I’m sure personnel at your shop have discussed possible causes, but perhaps they can consider these suggestions when you take the vehicle back to their shop.

Undecided Over Domestic Or Foreign Transmission Rebuilding Company   
Question 3
The transmission in my 2001 Honda Civic lost the lockup function of the torque converter.  Other than this problem the transmission shifts fine.  A mechanic at my reliable and trustworthy repair shop says the trouble is in the torque converter.  He says he will need to remove the transmission to replace it.

Because my car has 166,000 miles he suggests that I replace the transmission with a remanufactured unit from a company in the United States or foreign country.  The cost of the one remanufactured in this country is more expensive but the warranty on both transmissions is the same.  Another option is to send the transmission to a nearby rebuilder.  The cost and warranty is about the same but my car will be out of commission for up to a week. 

My car is in great condition.  I have owned it since it was new.  I have followed the factory service schedule but change the oil more often than suggested.  The engine runs great and it gets decent gas mileage.  I’m leaning toward replacing the transmission with a remanufactured unit.  The trouble is I can’t decide on which one.  Do you have any suggestions?  M.R., email

Answer 3
It’s your decision.  Perhaps your technician can help you decide.  He has more experience with his suppliers than I.

Also, consider an internet search.  You likely will find that the transmission rebuilt in this country is the most reliable unit.

Unsure Over Which Type Of Oil To Use
Question 4
Hello Dr. Gizmo.  I was wondering what your opinion is on synthetic motor oil.  Do you feel it is a good product to switch to?  If so are some brands better than others?  At what point would you switch in a brand new vehicle?  K., Marengo, IL

Answer 4
Since it appears your engine is lubricated with good old mineral oil you can switch to synthetic after the break-in period, but under normal operating conditions there is no need to use the more costly synthetic.  Good old mineral oil will provide the protections and lubrication your engine needs as long as you change the oil and filter on a frequent and regular basis.  You should follow the severe service schedule in your owner’s guide.  Personally, based upon many published studies and engineer recommendations I change the oil and filter every 3,000 miles in my vehicles.

If you should decide to pour synthetic lubricant in the engine, continue to change the oil and filter as frequently as you would with mineral oil.   You can use any brand of synthetic as long as it meets all of your car manufacturer’s requirements listed in your owner’s guide.  Oil containers are required to post all of the specifications on the label.  Compare the label to your owner’s guide requirements and you will have no problem choosing the correct oil.

Tests Pin Stalling On Failed Sensor 
Question 5
Recently, my 2006 Mitsubishi Lancer with a 2.4 engine began to occasionally stall.   It has 91,000 miles.  Three times I took the car to a local shop where a mechanic performed tests that determined a trouble code for a faulty cam sensor.  Each time the car was in the shop a mechanic tested the sensor but it passed tests.  He suggested that I wait until the stalling becomes worse before replacing the sensor.  He also suggested that I have the timing belt replaced.
Each time the engine stalled it would not restart right away.  If I cool the engine for 10 minutes or so it starts and runs fine.  It seems to occur after I drive for more than 20 minutes.  On cool days I can drive longer without any problems.
I’m afraid that if I don’t have this fixed soon the car will leave me stranded.  Do you think the stalling is caused by a faulty cam sensor?  Is it necessary to replace the timing belt?  S.D., email

Answer 5
Your car has already stranded you.  Fortunately, it restarted and you were on your way.  This problem has to be repaired.
I cringe every time a part is replaced that has not been verified with a fault, but in this instance the part is not too expensive to replace.  Testing in the shop may find a part is fine but once it heats up during a road test it may fail tests.  Ask your technician if he has the equipment to test the part during a lengthy test drive.  If so, he may find the camshaft position sensor fails after 20 minutes of travel.  You might consider authorizing his use of the car so he can drive it back and forth to his home and shop with test equipment monitoring the sensor.  If he captures a failure, that’s great!  If testing does not find a fault, consider replacing the sensor anyway as it has a history of fooling test equipment.  The cost is not too bad and it may cure the trouble.

As for the timing belt, according to the factory maintenance schedule it is due for replacement at 105,000 miles.  You can do it now as a preventive measure but surely in needs replacement before it breaks.  When the belt breaks it is possible for the valves to bend and in some severe cases pistons can break as well.  The result is a ruined engine.

Failure Of Computer After Spark Plug Replacement Is Coincidence
Question 6
I own a 2005 Pontiac Vibe with a 1.8-liter engine.  I have owned it since it was new.  I have taken great care of it with oil and filter changes every 3,000 miles.  I also follow the severe service schedule for all other maintenance.  The odometer reads 105,000 miles.  
Two weeks ago I had a repair shop replace the spark plugs as preventive maintenance.  The engine ran great before and a little better after the work.  The next morning when I started the car to go to work the check engine light turned on.  I returned to the repair shop where a mechanic checked the computer for trouble codes.  He found two codes that indicate a problem with an air pump.  He tested the pump, a solenoid, checked the wiring, checked vacuum lines and checked for blockage in some ports but could not find any problems.
The technician said that his equipment performs tests on individual components and everything is working as designed except it appears a control module is not telling parts to turn on and off.  Now he says the control module needs replacement.
I’m a female.  In the past I’ve had some problems with repair shops.  Does this make sense to you?  Could he have done something when he replaced the spark plugs that could cause this trouble or is this coincidence?  I.R., email

Answer 6
The complexities of vehicles can be intimidating for auto technicians so certainly the technology can be intimidating for you.  After all, computers in today’s cars are more robust than in many aircraft and even the retired Space Shuttle.   
It is highly unlikely replacing the spark plugs had any effect on the control module.  Replacing spark plugs does not require disassembly of the powertrain control module.  The powertrain control module (PCM) is a solid state unit that a technician does not disassemble for repair.  Certainly he can remove it by removing a plug and some bolts but he does not dig inside the unit.  It is a computer with various chips that is programmed and the program often is updated when a technician plugs into the system using factory procedures and software updates.  None of this type of work was necessary in the process of replacing the spark plugs. 
As for his diagnosis, it is entirely possible that a fault inside the PCM circuits is not commanding the air pump solenoid to open and close.  It also commands when to power up the electric air pump motor.  Just as it possible for a fault to develop in any electronic device, a fault can develop in the module.  His diagnosis likely is on target, replacement and programming a new or remanufactured unit will likely 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. 5/04/2012 ® DR. GIZMO © 1989-2012

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