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I have a 2001 Hyundai Trajet GLS 2.7 litre V6 DOHC 24 valve 4 speed auto. It has done around 170,000 kms, and been a great performer. Recently the engine has begun to lack power. I had all the plugs and leads changed, but the problem persists. It is as if the timing is off and the spark is too late. It is very slow to accelerate. The response is very sluggish. The fuel consumption has gone up, and I think I can smell unburnt fuel when I stop and am outside the vehicle. Any ideas?

There are a few possible causes. This vehicle has a timing belt and you should have the cam timing inspected to ensure it's correct. It's possible that the hydraulic timing belt tensioner has lost its tension and the belt has jumped a tooth. If the cam timing shifts too far out of syn it could result in engine damage.

Another service item to check for condition is the air filter - a blocked air filter will cause sluggishness and high fuel economy.