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Jim Grant Tech Tips Jim Grant Tech Tips
A collection of helpful articles based on reader submissions
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Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

89 Buick Century, Eight Months of Mystery
Q: My '89 Buick Century has been fine until the last 8 months. The problem: while driving, the car does NOT lose power but the speedometer drops down to zero for a few seconds. I can even accelerate. Just as the speedometer goes back up to the current speed, two lights on the dash (Check Engine Soon and Temperature) flash on briefly. Just at that moment the car seems as though it will lose power, but it doesn't. There's not much left to change on my car now. Have you ever heard of such a problem? Rich

A: You're describing the possible warning signs of a computer failure. The symptoms in your vehicle can vary, these are a few of the erratic (I stress "erratic"), conditions you may experience; loss of speedometer, high idle and/or low idle speed, stalling, bucking at highway speed, Check Engine Soon and/or Temperature light. Often a diagnostic check of the computer will fail to provide an explanation, no codes in the computer's memory. Or, the computer gets real creative and invents phantom codes that diagnostically lead nowhere.

So, how do we diagnose a problem computer? It has to be unbolted from its hiding place behind the dash. This is done for a couple of reasons. First, to impress the customer, next to check the electrical connections, but most importantly to have it out where you can hit the darn thing! Just like jump starting a newborn, the computer will get a slap. Of course the engine is running during this high-tech test. If the computer has circuit problems, the slap test can cause the engine idle to become erratic or even stall, which means the computer needs to be replaced.

GM computers in the late '80s had a few problems. That was corrected, more than once, with an improved computer design. Currently, the improved design is only available from GM. If you purchase an aftermarket computer you could be bolting on an old problem.

A word of caution: The computer isn't always at fault. A perfect example is the computer in my Buick. It has a dent in it from a flying coffee cup, that bounced off the computer and broke the face on my test meter. The real problem was due to corrosion on one of the sensor connections for the computer at the engine.

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