Tim never thought he
would have a problem with fixing cars. He had a knack for finding the problem,
usually within the first few moments and considered himself a very clever
mechanic who took pride in his work. People brought their cars to him from every
part of town and his boss admired his work.
Just about the time you
think you've got it all figured out, along comes a problem car that refuses to
be fixed. This happens to every mechanic who has been around the business for
any length of time. It's as if the gremlin of car problems sends a tough one
your way just to keep you on your toes and knock you down a peg or two if you
are getting too cocky.
The time was right for
Tim to get put in his place by that gremlin. The car was a late 80's Camry and
it had a multitude of seemingly unrelated problems. The owner insisted that all
the problems started after he tuned it up. All he had done was slap in a set of
plugs, check the timing, change the oil and filters and sent it on its
way.
Now it had a bad case of
the hesitations. Once it got up to speed, it performed just fine. Also, it kept
running down the battery and was hard to start. As soon as the car was back in
his stall, he checked for stored codes in the computer.
There were no codes. One
thing he did notice was the radiator cooling fan kept running, even though the
temperature gauge was in the normal range.
He decided to check a
wiring diagram to find out what would make the cooling fan run all the time. He
kept asking himself, "Why me, what did I do to deserve this?" The wiring diagram
wasn't much help. The cooling fan running all the time seemed to escape logic --
at least as far as he could tell from the wiring diagram.
For some reason Tim
decided to start with the thermal sensing switch. As luck would have it, when he
grounded the wire going to the switch, the fan stopped running. Closer
inspection of the wiring connector turned up a clue. The connector had been
wallowed out and was probably not even touching the switch.
Using needle-nose pliers,
he tightened the connector and plugged it back onto the switch. To his relief,
the fan quit running.
What about the car's
new-found hesitation? Maybe a good 'ol injection cleaning was in order. An hour
later, after hooking up the cleaner and giving the injectors a good dose of
cleaning solvent, the problem remained unchanged.
"Maybe it has something
to do with the timing?" he thought. He tried bumping the timing up and back a
few degrees, both without any real effect.
"How about an exhaust
restriction?" he thought. Minutes later he was under the car breaking loose the
catalyst. A test drive revealed no change. "What would my vo-tech teacher say?
What would he tell me to do? Probably say, 'back to basics boy'." Okay. Back to
the basics. After checking the compression, he spent the rest of the day with
the scope and exhaust analyzer.
Maybe it was a lazy
oxygen sensor. He ordered a new one and decided to call it a day. On his way
home, he was going to stop in and ask his friend, Sid, about the car. Sid was a
Toyota specialist. Tim was glad he stopped and talked with Sid because he was
given a whole laundry list of things to check. He could hardly wait until the
next day to dig in again.
First he replaced the O2
sensor, but it only helped a little, but the sag was definitely still there.
Going down the list, he removed and checked the air boot between the vane air
flow meter and the throttle body. No cracks. Next he carefully removed and
cleaned all the engine compartment wiring connectors, paying special attention
to the one under the battery and on the airflow meter.
Still, the test drive
proved nothing had changed.
"What about the vane
airflow meter itself?" he thought. He took it off and inspected the action of
the air door. Even though it didn't hang up or have any roughness in its
movement, he decided it should be replaced.
Later that day with the
new airflow meter secured in place, the problem persisted. "It must be the
stupid computer after all," he reasoned. The following day he installed a new
computer and found out his hunches were still wrong, wrong, wrong.
The car owner was getting
really mad about all the time he was taking with the car and was making nasty
threats to his boss. The boss was getting very testy, especially since Tim had
already sunk a small fortune in trying to capture the Camry's evasive gremlin.
Tim decided to pay Sid another visit.
Sid said it sounded like
a carbon problem. "Camry's are supposed to grow carbon in the combustion
chamber, intake manifold and intake valves. Pull the manifold and clean all the
carbon out.
It's probably full of
carbon." Sid was right about the carbon. It had a good share of it, especially
on the intake valves. Using spray carb cleaner and several small wire brushes he
was able to clean the intake area pretty good without having to remove the
cylinder heads. He figured he had it for sure this time.
"Wrong again honey!" he
said out loud as he stepped on the gas and the car lost power.
"Man, this one has really
got me down... time to pay Sid another visit, this time with the car!"
Sid's mouth dropped open
when he saw him pull up in the car with a sour look on his face. As Tim got out
of the car he held up a thumbs-down sign.
At first Sid was
speechless. "Nothing has helped? You did everything I suggested?" Tim replied,
"Nothing. Nada. Nix. Zip. Zilch."
Suddenly Sid's face
brightened. "Let me look at the rotor." Tim said,
"Sid, this is not an
ignition problem. The stinkin' car just hesitates -- and is a bear to get
started when it is cold. Maybe the cold start injector, maybe the throttle
position sensor. But why the rotor?"
Sid replied "Just a
hunch..."
Sid unscrewed the
distributor cap mounting bolts and grabbed a jumper lead from his box. He
clipped one end of the jumper to the coil secondary terminal and held the other
end just above the center of the distributor rotor.
"Crank it over!" he
yelled. Tim twisted the ignition key while the starter motor cranked.
"Hold it!" shouted Sid.
"Come check this out."
"Here, Tim, hold this
lead just above the rotor. Now I'm going to crank the starter. You watch for a
spark."
Tim said "Yep, got a
spark. So what? I know the spark is good."
Sid countered, "Yeah, but
the rotor isn't supposed to conduct like that. It's grounded right through to
the distributor shaft.” “Look,” he said as he pulled the rotor from its place
and examined the underside.
Sure enough there was the
faintest trace of rust where it mounted on the shaft.
"But how can that cause
hesitation?" Tim asked.
"Easy," Sid replied.
"When you give it the gas, there is a need for more spark to fire the richer
mixture. The extra resistance in the spark plug gap makes the secondary seek
another path to ground. The rotor leaks just enough voltage to cause a slight
misfire and hesitation."
"And when I hook it up to
the scope, everything's normal because it isn't under load," said Tim.
Sid reached into a top
drawer and pulled out a used rotor and gave it to Tim. "Here, lets put this back
in the car and you take it for a spin and see if the problem is gone. If not,
come right back." Tim didn't return.
The car owner was charged
for the injector cleaning, carbon removal, distributor cap, rotor and oxygen
sensor. His boss put the computer and airflow meter somewhere in the stock room,
hopefully for some future need. Tim got paid two hours for his efforts and went
home with a lesson he will never forget. Chalk one up to the car
gremlin.
