Automania/Repair & Maintenance

AUTO QUESTIONS AND ANSWERS FOR WEEK 12

by Bob Hagin

Q. I drive a 1992 Ford F-150 that has a 300 CID six-cylinder engine, a manual transmission and 65,000 miles on it. The motor, without fail, sporadically hesitates and basically jolts the truck while driving a smooth road, at a constant speed, in any gear providing that the engine is running between 1500 and 2000 RPM. It does this with the cruise control on or with the driver trying to maintain a constant speed with the accelerator. The most severe jolts occur a minute or so after the motor's temperature gauge reaches its normal operating temperature. The truck has been tuned up by dealership shops several times, a fuel pump in the rear tank has been replaced and the mechanics claim that the fuel pump pressures are all within their appropriate ranges. I have always thought that the problem must be somewhere in the fuel system. A month ago I bought a fuel additive. To me, these products are a waste of money but the severity of the hesitations and jolts were reduced and are only now at a level where I begin to notice them. J.L. Lincoln, CA

A. The only times I experienced a similar problem it was a combination of several things. The intake manifolds were leaking slightly which caused the spark plugs to overheat and detonate the mixture. The manifold on your Ford is pretty long, so you look into this. It may pay to go to a slightly colder spark plug if a close examination of their tips with a magnifying glass shows tiny spots of aluminum that are being blasted off the pistons. The additive you used probably raised the octane rating of the fuel you're using, which would cool the plugs and clean up your fuel delivery system. Rather than a run-of-the-mill dealer's shop tune-up, what you need is a diagnostician.

Q. I've heard that built-in child safety seats are safer than aftermarket car seats, but I have misgivings about the ones in our '97 Chevrolet Venture. I discovered that the clip that holds the straps together at chest level pulls apart with my bare hands without depressing the buttons. GM informs me through its customer service center that the straps are designed to pull apart during an impact so that the child's chest is not injured. However, the aftermarket car seats that we purchased several years ago are not designed to do so. Obviously, with my children's safety at stake, I'm very concerned. P.C. Virginia Beach, VA

A. The logical way to see if the shoulder harness connector on a seat like the one in your Chevy van is to try another one like it. Unfortunately, I couldn't find a Venture with a built-in child's safety seat in any of our local dealerships and I'm told that built-in child safety seats aren't in as much demand as they were a few years ago. I checked the internet at http://www.vehiclechoice.org/safety/ and found a National Highway Transportation Safety Administration (NHTSA) child's safety seat recall on a '97 Chevy van, but I don't think it covers your particular problem. When you click onto the site, you can file a query to the NHTSA electronically. It also provides a method of checking for general recalls on vehicles.

Q. We have a 1991 Dodge Colt Vista wagon with an automatic transmission and a four-cylinder engine. We bought the van last summer and are pleased with it, but we've discovered that when the weather turns cold, the transmission takes a very long time to shift until the temperature of the engine gets to normal. We took it to the mechanic who maintains our wagon but he says that he can't find anything wrong. By the time we get to his shop, the engine is warmed up. T.H. Milton, WA

A. Your transmission shift delay is normal in that vehicle. It's programmed to delay the upshift for up to two minutes if the automatic transmission fluid is under 95 degrees Fahrenheit.