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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