QuestionQUESTION: I have a 99 Hyundai Sonata with 160,000 miles on it. I just had my 3rd timing belt put on it and while they were in there, I had them change the water pump. When I got the car back, the car had poor acceleration and a bad vibration while accelerating from 20 MPH to 60 MPH. It seems to smooth out at 60 MPH to 70 MPH then gets bad again at 80 MPH. I feel like I am pulling a tractor trailer. I've had it back to the shop 3 times and still the same, with no change. Any ideas? Can the Timing belt be off a tooth?
ANSWER: Hi, Rob. I'm going to ask some questions to help me determine where the problem may be.
1. Do you have the 4 cylinder 2.4L engine or the 2.5L V6 engine?
2. Is this a very high frequency vibration (unlike a wheel balance issue or a misfire)?
3. Does the vibration occur when the vehicle is idling in drive or neutral?
4. Does the vibration occur when you rev the engine to higher rpms in neutral while not driving?
5. Do you notice a lack of engine performance?
6. Can you establish whether the vibration varies with engine speed or vehicle speed? To do this you'll want to pay particular attention to what happens when the transmission shifts to the next higher gear. If it varies with engine speed, it'll increase as vehicle speed increases, but then jump to a lower frequency as the transmission shifts. If it increases with vehicle speed, it'll continue increasing just as before when the transmission shifts.
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QUESTION: 2.4l. No vibration at idle. It does vary with engine speed. There is a lack of performance.
ANSWER: If this is a high frequency vibration, the one or both balance shafts may be out of time. This wouldn't affect engine performance, however.
If this is a lower frequency vibration such as a single cylinder misfire, it likely has nothing to do with the timing belt and may be due to a problem with the secondary ignition system (plugs, wires, coils).
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QUESTION: Thanks for the great response. I think we are on the right track. I have been paying close attention to the concern at hand. What I have found, is there is no lack of performance. The gas mileage is not changed. The frequency and intensity of the vibrations seems to increase in frequency with RPM. Not quite as bad with the AC off, but with the AC on, seems to be significantly worse. Took the car to the dealership. Was told one of the balancers were off by 3 teeth. Picked the car up, vibration still there, doesnt seem as bad. Tech told me I should drive the car for a couple of weeks and run the car hard to blow the bad stuff out of the engine. How many balancers are there? Does one affect idle and one affect driving? Are they hard to balance? I am a bit confused. Tech also told me it is quite normal to have vibration after timing belt repairs. Hmmm...I am at a loss. Any input would be great.
AnswerThe only vibrations I've ever noticed which were worse with the A/C on were with the car idling in gear. Some degree of this is normal on the four cylinder Sonata. It isn't normal to have vibration after timing belt repairs unless the engine is timed incorrectly, and it won't get better with driving. Sometimes, on older cars, the motor mount rubber begins to crack and sag, and this can cause a greater transmission of the engine vibration to the body.
As for the balance shafts, there are two. Both affect engine vibrations, but these vibrations will be of very high frequency, about 4 times the vibration frequency of a misfiring cylinder, and if not timed correctly, the vibrations caused will be worse at higher engine RPM.
