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BACKYARD MECHANIC: Check Rio's plug wires, emissions system

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2011 Kia Rio EX-Convenience at for $10,488

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QUESTION: I have a 2004 Kia Rio that has served me very well and normally runs flawlessly, but this weekend I had a very unusual experience.

I was on a ferry, and when it was time to drive off, I had difficulty getting the engine started and it idled roughly. I barely made it up the incline ramp, and when I got on the highway, it took awhile to get it up to 90 km/h, because if I pushed the accelerator down any harder, it would bog out like it was starved for fuel.

My tank was three-quarters empty and fortunately the nearest gas station was only 20 minutes away. By the time I got there, it was barely running and it died as I backed it up to the pumps. I filled it up, which only took 25 litres, meaning there should still be 10 to 15 litres left in the tank, so it shouldn't have been out of gas. Thankfully, the car started up after some cranking and then ran flawlessly, including my return trip back a couple of days later. Previously, on several other trips, the check-engine light has come on when I got below half a tank, but it still ran fine, but then after I filled it up, the light would go off on its own within a day or two.

I haven't filled up since the trip and am waiting to see if the check-engine light comes on again and if the rough idling reappears. Do you have any suggestions for the do-it-yourselfer to check out before taking it to the dealer? Typically, they want to charge $90 just to read the Check Engine codes.

ANSWER: It sounds like there may be two unrelated problems occurring on your vehicle.

The rough running and lack of power was probably caused by ignition misfire rather than a lack of fuel. The high humidity on the ferry crossing may have been causing the spark-plug wires to short to ground. Stopping for fuel allowed the hot engine to dry out the engine compartment and the ignition system started working properly again.

Good spark-plug wires are resistant to misfiring due to moisture, but the insulation breaks down with age. You probably need to replace the plug-wire set. A quick check for electrical leakage from plug wires is to open the hood on a dark night and take a close look at the plug wires with the engine running. Don't be surprised if it looks like a miniature lightning storm as electricity leaks from the plug wires. Misting the engine with a little water and 10 per cent salt solution will make any problems even more obvious.

The other issue is the check-engine light coming on when the tank is low on fuel. I would suspect this is caused by a fault in the evaporative emissions system and how it uses vacuum and pressure in the fuel tank to monitor system sealing. If there is a small leak in the vent and vapour lines or the fuel cap for the fuel tank, the system will set a code and turn on the check-engine light. If the leak is small, it may only set codes if the fuel level is lower. Check all hose connections and the gas-cap seal first. Technicians often use a smoke generator to fill the tank and locate small leaks, so this may be the quickest way to find your problem area.

QUESTION: I am looking at buying new shock absorbers for my Ford. The parts store has regular, heavy-duty and gas-filled shocks. Is it worth the extra money for the gas-filled shocks?

ANSWER: I would recommend buying the best shock absorber you can get. The vehicle will have a better ride, handle bumps and corners better and be more controllable during emergency manoeuvres.

Gas-filled and heavy-duty shocks have bigger, stronger internal parts that last longer than regular shocks. The gas-filled shocks are charged with nitrogen gas that prevents the oil inside from foaming as the shock works. Gas shocks may be the most expensive but work the best.

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.

kerr.jim@sasktel.net

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