Automania/Repair & Maintenance

AUTO QUESTIONS AND ANSWERS FOR WEEK 03

by Bob Hagin

Q. We own a 1995 Mercury Marquis LS V8. The odometer shows 41,000-plus miles. Since it's time to start replacing the spark plugs, I have taken the time to see what is being offered. To my surprise, I find that there are spark plugs on the market ranging from $1.95 to $9.95. One company is advertising a platinum-tipped plug for $3.95. Is it cost effective to pay almost $10 for a spark plug? H.S. Lodi, CA

A. I've always been of the opinion that a spark plug is little more than a nail driven through a piece of porcelain and that some of them just use fancier nails than others. The main criteria for an effective spark plug is that the inner electrode (the part that's down in the fire and explosion) should maintain sharp corners as long as possible. A high-voltage spark jumps from square corners more easily than it does from rounded corners. I've never seen any unbiased reports that verifies the fact that any particular type of high-quality spark plug lasts significantly longer or produces more power or fuel mileage than another given that their heat ranges (another factor in spark plug selection) are the same. As a rule of thumb, if you go with the plug recommended by the factory, you won't go wrong. Unless you're installing them yourself, the cost of the installation is probably more than the price of the plugs.

Q. Our 1990 Ford F-250 pickup is a 4X4 Supercab with an automatic transmission and a camper on the back. It's the long wheelbase version and we use it a lot to go camping and to pull our small boat on a trailer. It has approximately 90,000 miles on it. During our last camping trip, we noticed that the truck seems to have a slight shudder or vibration when I just begin to accelerate fairly hard. It diminishes once I get going. It's a percular feeling and it doesn't feel like it's coming from the engine. Is this something I can fix myself? H.J. Eugene, OR

A. Any vibration or shimmy that suddenly surfaces in a vehicle should be checked out right away since it could lead to additional damage. Off hand, I'd say that your truck has a problem in the driveshaft somewhere. A universal joint will give that sensation if it has gone dry of lubricant and become worn on the thrust sides of the "X" shaped trunnion. The vibration usually goes away on deceleration because the back side of the trunnion isn't damaged. Since the driveshaft on your F-250 is very long, it's also possible that there is a problem in its center support bearing. If its angle is too severe, it would in effect be winding up and unwinding four times with every revolution of the shaft and you'd feel it as a vibration. Leave the job to a pro.

Q. I have a problem with the AM radio in my 1997 Chevrolet Suburban. There is a noise on any AM station when the vehicle is not close to the station's transmitter. The noise is not present when the vehicle is parked with the engine not running. The FM reception is always good. I've taken it to two Chevrolet dealers for a total of five times in two years and they haven't been able to fix it. I have contacted Chevrolet Motor Division and they say that based on reports they've gotten from their dealers, my radio reception is within specifications. This fall I drove a new Suburban with the same radio and there was no noise on the AM radio at all. P.D. Schenectady, NY

A. Usually, a shop will try another radio (new or an exchange in- stock) in a vehicle. If the noise goes away, it's the radio. If it doesn't, something in the engine (bad plug wire, faulty capacitor, etc.) is giving off a magnetic signal at a frequency the receiver can pick up. You may have to go to a auto radio shop to get it analyzed or fixed, but I've sent your letter to my contact at Chevrolet for comment.