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CONSUMERS : When the Diagnosis Is the Problem


Question: My 1985 Mercury Topaz with 73,219 miles has been running smoothly until recently. At about 55 miles per hour the engine will buck, lose speed and then die. It will not restart for five minutes.

When the problem began, the engine speed would jump around erratically, but I could nurse it back. Now it just dies. I have returned it to the shop for repairs, but I was assured nothing was wrong. I'd appreciate any help.--E.F.G.

Answer: It could be any of a number of problems, some of which should show up on the engine's self-diagnostic system. But if your mechanic relies solely on the computerized self-diagnostic system, he or she might not be getting at the real cause of the problem.

Self-diagnostic systems are great, but mechanics can come to rely too heavily on them and become unable to perform their own diagnosis of a car's problem. At that point, they really are not so much mechanics as they are test station operators.

Often, a mechanic will say that everything checks out on the computer, so there must not be a problem. The condition you describe could very well be a vapor lock, a condition in which the fuel system is obstructed by overheating in the fuel lines. The diagnostic system on your Ford cannot detect vapor lock.

If it finds a problem in the engine, the diagnostic system should store an error code in its memory. When your mechanic hooks the car up to the service computer, the error code is revealed and the mechanic can then perform additional tests. Typically, something called an OTC-2000 tester is plugged into an electrical connector under the dash.

For example, a Code 14 or Code 18 is an ignition module problem, which is common when a car will not start when the engine is hot.

If you are an enterprising back-yard mechanic, however, you can get the error codes out of the computer by using a jumper wire and running it to the common ground terminal on the connector. You'll need a shop manual to perform the test and understand the codes that will flash on the dashboard check-engine light.

No matter who performs the test, if the computer does not reveal an error code then the real detective work will begin.

You really need to find a Ford dealership you can trust to do this diagnosis. I would suggest you look for one that has ASE certified mechanics and is part of the AAA repair station program. Check several dealers for their prices before taking in your car, as well.

Q: I have a 1986 Toyota Celica that needed a new clutch. After the clutch repair, my gas mileage dropped by 30%. The engine no longer feels the same, either. When I shift up, it feels as if there is not much power. I asked my mechanic to recheck the clutch, but he could find no problems. Is the fuel economy problem related to the clutch repair?

A: It is not likely, but a clutch repair on a Celica is not an easy job. The entire engine must be lifted, requiring the mounts to be freed and then reattached after the job is completed. It's possible the entire assembly job was botched, causing a secondary problem in the engine. You should obviously check to make sure the engine is tuned, making sure the fuel system is functioning properly and the timing is correct.

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