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Under the Hood: Avoid 4x4 mode on the road

Brad Bergholdt, Tribune News Service on

Published in Automotive News

Q: I read your column in the local newspaper, the Texarkana Gazette, and that's honestly the only reason I buy the Sunday paper.

I have a 2001 Chevrolet Silverado 5.3 automatic four-wheel drive Z71, approximately 160,000 miles, perfect maintenance so far. We had some winter weather, and I have some land, and I put my truck in four-wheel drive high, probably the fourth or fifth time ever I've had it in four-wheel drive. I parked it and went inside and forgot that it was in four-wheel drive high the next morning. I jumped in my truck and drove approximately eight miles, at the most 70 miles an hour. I noticed a little bit of tension when I was turning the steering wheel but just blew it off as being cold outside. I was at the store turning left and noticed the resistance and then I saw the button on the dash -- it was in four-wheel drive high! I immediately I put it in two-wheel drive high and went on. What are my concerns? Could I have damaged the transfer case or the front axle and the CV axles up front? What should my concerns be? It runs fine and does OK now.

Joel Andrew K. Doddridge, Ark.

A: Joel, don't sweat this! Your time driving on pavement in 4x4 mode was short enough there should be no problems. Your truck is a true 4x4, as opposed to the many all-wheel-drive vehicles out there that power all four wheels at all times but are fussy about having exactly identical tire size/wear to avoid driveline wear.

Operating in 4x4 mode on dry pavement does considerably stress driveline components as well as tear up the tires. As the truck turns corners or makes any turns at all, each wheel needs to turn at a slightly different speed. When four high or four low are selected, the front and rear axles are locked together. The stiffness and wrap-up you detected is fortunately mitigated a bit by tire slip. This is a situation that should definitely be avoided, to avoid rapidly accelerated wear on a bunch of components, but you caught it quickly!

Q: My 2002 Chevrolet truck makes an occasional jerking feeling when I'm driving about 60 miles per hour, and not at any other speed. I feel it when I'm just pressing a little extra on the gas, as when climbing a slight hill. There is no engine light, and it starts and runs fine at all other times. Do you have any ideas for me to check? Thank you!

Mario, San Jose Calif.

 

A: This is a longshot without being there to observe and test! I'm thinking perhaps engine misfire, and since it's so infrequent, that's why your OBD-II (on-board diagnostic system 2) hasn't yet identified it as an emissions concern and turned on the check engine light. If you can get your hands on a scan tool that indicates cylinder misfire information (either a premium level generic OBD-II scan tool such as the Blue Driver) or a professional grade scan tool, misfire counts can be observed. Each cylinder is listed, and should one indicate misfires are occurring, I'd try swapping that ignition coil with a neighboring cylinder and driving the truck again under the same conditions. If the misfire moves -- follows the coil -- that's a slam dunk that the coil is at fault (leaky coils are fairly common). If the misfire remains, swap or replace the spark plug and repeat the drive. If the misfire remains in that cylinder, professional skills will be needed to take the diagnosis further.

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Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.

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