QuestionQUESTION: Hi, I asked this the other day and I accidently deleted your answer. I have a 2000 Hyundai Elantra with 35,000 miles. My question is what what would make a clattering, ticking type of noise only when my foot is on the gas. When I rev the engine in park or with my foot on the brake when the car is in drive it will not do it, only going the road it does it. One more question after the car has been driven and is hot and I turn it off and I if get back in a short while later, before the car cools down, it will act like it does not want to start and idles really rough. What is the deal??????
ANSWER: It's hard to say what might be making the noise you describe. Since it only occurs whin in gear and moving, the transmission is a prime suspect.
The not starting issue sounds like it may be a fuel management issue, so I'd recommend checking to see if there are any diagnostic trouble codes in the engine control module (ECM). If your check engine lamp is coming on, codes will be present.
For your reference, here's my prior answer:
There are a large number of items that could make the vehicle not want to start and run rough. It's possible you have a defective fuel pressure regulator or coolant temperature sensor. If your check engine lamp is on, you should start by reading the trouble codes. AutoZone and AAMCO have advertised they'll do this for free.
As for the noise, the best I can do is tell you it's probably coming from something in your engine or driven by your engine. Without being able to listen and follow the noise, it's difficult for me to develop a good mental image of it's sound, as well as difficult to narrow what specific items may be making the noise.
For the issue with starting, if you've got no trouble codes, you should have your car checked by a good driveability shop. Most general mechanical shops should be able to diagnose the noise.
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QUESTION: The check engine light has never been on at any of these occurrences. I had the regular scheduled maintenance on the transmission at 30,000. I had it done at an Aamco, they did not say anything was wrong, it shifts smoothly. I have taken my car to the local Hyundai dealer and they told me the clattering noise was from carbon build up, could that be true?? If so, wouldn't it make that noise all the time not just when my foot is on the gas going down the road.
AnswerBased on what you were told by the dealer, it sounds like the noise you're hearing is spark knock. This occurs when the gasoline begins to ignite too soon due to excessive combustion chamber temperature or improper ignition timing. Typically, several factors need to come together to create the excessive temperature. First, it tends to only occur when the engine is under load (foot on accelerator) at low engine rpm. Then, there needs to be some additional impetus to raise temperature further, such as increased compression due to carbon in the cylinders, cooling system not functioning properly, overadvanced ignition timing, or some other cause.
If you try using higher octane fuel (89 or more) and the problem is eliminated or reduced, you've verified it is in actuality spark knock. Higher octane fuels burn more slowly and hence have a greater resistance to igniting under pressure and heat without spark.
Your car is equipped with a knock sensor which is monitored by the ECM so that it can adjust ignition timing accordingly. One of the things to check in this situation is whether the knock sensor is functioning normally. Unfortunately, this isn't something most laypeople will be able to do themselves.
