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THE 308 TIME BOMB
THE 308 TIME BOMB
The Ferrari 308 had earned an ugly nickname at the dealership..."The time
bomb." It would run perfectly for several months and then, boom! It would blow
the catalytic converter right off the back end of the vehicle. When the catalyst
exploded, it would do so with such force that nothing but the header pipe would
be left. The rest of the fragments would become roadway shrapnel, never to be
recovered.
The foreman who was assigned to the problem had seen it through the first three
catalytic converters. The car was still under the five year/50,000 mile
emissions warranty, so the dealership kept having to replace the catalysts.
There never was enough of the catalyst left behind to give a clue as to what
caused the explosion.
After the car came back with its fourth exploded converter, the foreman was told
to assign the job to another mechanic. The foreman, Willis, didn't want to give
up the car, telling his co-worker that he never could make it happen. "I drove
it and drove it. It never acted up. I think the owner is nuts. I think he is
taking it out and going over a hundred when it happens. I can never find enough
road to get it over 60, at least not around here."
It was true. Traffic on the busy Hollywood 101 freeway made it nearly impossible
to attain speeds above 60. Why did the car have it in for converters? It was as
if the car was a wild stallion that refused to be tamed by a catalyst. The 308
engine had a continuous fuel-injection system with two separate ignition
systems, one for each bank of cylinders.
Ace, the next mechanic on the shop totem pole figured the problem had to be
related to the ignition system. He remembered how Dan, his high school friend,
used to get going about 50 mph and turn off the ignition. Just before the engine
died, he would turn it back on. Bang! It would make a terrific explosion and
scared the daylights out of the girls. Finally the muffler blew apart.
Systematically, Ace went over each connection in the primary ignition system. He
tested every connection and everywhere he looked everything was in perfect
order. He was looking for something that was loose, or a connector that had
backed out of its holder. He reasoned that vibration was causing a harmonic to
develop in the car and the wiring harness was breaking down somewhere.
Finally he worked his way back to the car's computer, which was located in a
side panel in the trunk. As he removed the computer from its moorings, the
engine faltered for a second. Every time he wiggled the connector to the
computer, the engine faltered. Aha! It must be a faulty wiring harness.
He proudly showed the foreman what he had found and was told to order a new
harness. Before he placed the order, he decided to test the multigang plug on
the computer side of the harness. It was just a hunch. Maybe the connector on
the computer was the cause, not the harness. Ace's hunch was right on the money.
The computer connector had a cold solder joint and was making intermittent
contact.
When the driver got the Ferrari going fast enough, a harmonic vibration was
created in the rear end that was sufficient to cause the connector to open up.
When it did, the ignition system would shut down. Since the car had a mechanical
continuous fuel-injection system, fuel continued to flow. In the time it takes
to blink your eye, the catalyst would fill up with a perfect mixture of fuel and
air. When the computer made connection again, spark came back and the engine
started firing again. Nanoseconds later, flames from the exhaust would hit the
converter and BOOM!
"But why couldn't we duplicate the problem on a test drive?" asked Willis, the
shop foreman. The owner finally came up with the answer, "Because it always
happened late at night when I went from San Francisco to Palo Alto... at speeds
between 100 and 150 mph."
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