"Dr. Gizmo"
By Phil Arendt
Computer Glitch Causes Rough Idle, Difficult
Starts And Stalling
Question 1I have a 2007 Chevrolet Impala with a 3.5-liter flex-fuel engine. When the engine is cold such as after being parked all night when I start in the morning often it runs rough, misfires and sometimes stalls. This does not happen all of the time but happens too often and lasts less than 10 seconds or so.
Multiple times I have gone
to a repair shop or dealership to have the trouble diagnosed and repaired. The spark plugs have been replaced. They have checked for air leaks. The computer has been reflashed. The computer has been replaced. The fuel pump was replaced and more. They have done just about everything under
the sun but the trouble persists.
The car has been doing this
since it was new. Now it has almost
100,000 miles. It’s in great condition
and I want to keep it but especially in cold weather when I start the stalling
and sputtering is almost unbearable. Do
you have any suggestions short of dumping the car? T.M.F., email
Answer 1
The joys of owning a
flex-fuel car often ends before the first car payment. Apparently, this is the situation in your
case, but there is hope.
Your car uses a virtual
system that tries to calculate the percentage of alcohol blended in the
fuel. Other systems use sensors to
measure the alcohol content. Whether the
system uses virtual measurements or actual sensors the measurement is used to
adjust the air to fuel mixture going to the cylinders. Since your car uses virtual measurements
based upon computer algorithms there is trouble that can’t be repaired but
there is something you can do to hopefully end your woes.
The trouble might be caused
by topping off the fuel tank with different alcohol blends. One time you might top off with a fuel
blended with 10 percent alcohol and the next time with fuel that is 85 percent
alcohol. Soon there will be fuel blended
with 15 percent alcohol that will bring on other issues but I won’t go down
that path right now. The point is your
computer system can’t accurately identify the fuel blend to properly adjust the
air/fuel mixture.
To counter this problem, run
the tank to nearly empty and then fill it up with the fuel of your choice. The best thing to do is stick with one brand
of fuel and same alcohol content. If you
must switch alcohol content let’s say 85 percent alcohol to 10 percent alcohol
run until the tank is nearly empty before filling up. In doing so the computer system won’t do as
much guessing and the engine should run fine when you start in the
morning. If this does not cure the
trouble your dealer might be able reprogram the engine control module with
updated information to address this issue.
Installed New Parts And
Engine Fails To Run
Question 2I have a 2002 Hyundai with a 2.4-liter engine that is misfiring and now that I replaced the ignition coils, spark plugs and ignition wires it does not start at all. I took the newly installed coils back to the auto supply store where they exchanged them. I installed these coils and the engine still does not start.
As an experiment I put the
old coils back on the car and the engine starts but does not run very
well. Is there something I am doing to
the new coils that causes the engine to not start? B.L., email
Answer 2
The fact that the old coils
at least start the engine says a lot about the newly acquired aftermarket
parts. Consider ordering new original
equipment coils from a dealership. Sometimes
aftermarket parts just do not meet original equipment standards. It’s time to return them to your parts supply
store for a refund and install factory original coils.
Temperature Gauge
Inoperative
Question 3 The temperature gauge in my 1994 Volkswagen Euro Van quit working. I replaced the temperature sensors on the engine. I also removed the instrument cluster to examine it but did not see anything burnt or loose. When I ground the wire at the temperature sensor the gauge moves to hot and the warning light turns on.
I’m frustrated. What am I missing? M.R., email
Answer 3
Don’t let your VW give you
fits. It’s possible the new sensor has a
fault. A test with an ohm meter should
determine if it is functioning.
Since the gauge moves when
you ground the wire at the sensor the wiring seems okay. If the sensor passes tests, more than likely
a lasting repair is to replace the instrument cluster.
Transmission Sticks In First
Gear
Question 4The automatic transmission in my 2004 Buick Century takes a long time to shift from first to second gear. This does not happen all the time. When it does occur it is usually after the car has been parked for a while. I start the engine and place the transmission shifter in drive and the transmission sticks in first gear for what seems forever. Eventually, it shifts into second gear. Once it goes through this routine the transmission shifts normally the rest of my drive.
I had the computer tested
but there are no computer diagnostic codes.
Also, no warning lights shine on the dash.
My car is in great shape and
has 120,000 miles. Can this be repaired
without an overhaul? M.M., email
Answer 4
Trouble such as this could be caused by sticking valves or faulty solenoids in the transmission’s valve body. Repairing or replacing the valve body does not require complete disassembly of the transmission.
It is also possible the
cause of the trouble is deep inside the unit.
If testing finds this is true at this mileage excessive wear is a
consideration and disassembly more than likely will lead to an overhaul or replacement
with a remanufactured unit.
New Sound System Might Be Trouble
Question 5
Recently, I purchased a 2002
BMW 325i with 60,000 miles. The car is
in great condition and was running great until I installed a high powered sound
system. Right after installing the sound
system the battery and alternator died.
A shop replaced them, but now the antilock brake warning light is on in
the dash and I can tell the system is not working.
Are all these troubles
caused by the audio system? What else
could cause these problems? F.O., email
Answer 5
These troubles may not be
coincidence. If the sound system is not
installed properly and has issues such as improper ground circuits, trouble in
other circuits follows. Not only this
but if your sound system draws excessive electrical power, fluctuating power
causes issues in control modules and circuits that may cause failures.
If you installed the sound
system consider taking the vehicle to a shop that specializes in infotainment
installation and repair. A technician
may need to modify the installation by installing parts that stabilize and
regulate power and he may find ground circuits need attention as well. If a shop installed the system, return for
diagnosis of the trouble.
Repair Cost Might Be More
Than Anticipated
Question 6I have a 1999 Oldsmobile Aurora with a 4.0 engine. I purchased the car three years ago when it had 54,000 miles. It’s in great condition. It now has nearly 70,000 miles.
There is a troubling noise
coming from the front of the engine.
It’s sort of a buzzing sound. I
went to a repair shop where a mechanic replaced the power steering pump, drive
belt, tensioner and an idle pulley.
Despite all of this the buzzing was still there. He did not charge me for any of this work and
reinstalled all the old parts. He ran
the engine without the drive belt and the noise remained. Now the mechanic says the timing chain is
causing the sound. To find out for sure
he will need to do a lot of work to examine the chain.
Does this seem right to
you? K.R.T., email
Answer 6
Removing the serpentine belt that drives pulleys and accessories at the front of the engine eliminates sounds that can be caused by these parts. It also gives a technician a chance to use a stethoscope to check for noises inside the front of the engine.
It appears your technician
is going down the right path. Once he
examines the chain and all of its related hardware he will be able to determine
for sure if it needs replacement which is very likely.
Before he dives into
disassembling the engine be sure to get an estimate for the work including the
cost of replacing the timing chain. You
might learn that the cost of this repair exceeds the market value of the car.
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 mailto:drgizmo@hotmail.ws. 2/31/2012 ® DR. GIZMO © 1989-2012
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