Engine bogging - '04 Sonata

swilburn

This is a 2004 Hyundai Sonata GLS (V6). I just replaced the spark plugs, wires, and coil pack to address a misfiring issue. Those engine codes have now successfully corrected (no more error codes). Now the engine starts, but does not want to rev much beyond 2000 rpm - it sounds like it is bogging to me. I am also hearing a periodic "escaping air" sound beneath the car - maybe from the exhaust. The "escaping air" does seem up near the engine (not toward the back of the car). The engine also may be idling a little rough - but it will idle. I did have this bogging issue before changing the plugs, wires and coil pack, but had assumed at that time that it was related to the misfiring. Fairly obviously, that is not the case. I have checked for error codes with an OBDII, but am not now getting any error codes. I have read online of similar issues with revving and it was attributed to a possibly blocked/clogged exhaust.

thecardoc3

It does sound like you are describing a restricted exhaust system. What you need to do now is test and prove it. If the upstream O2 sensor can be removed and make sure that the exhaust gasses coming out wont damage anything, or can be deflected, start the engine up and see if that allows the engine to accelerate normally. An alternative is to attach a pressure gage in place of the sensor. The exhaust pressure should not rise above one psi. If it does the exhaust is restricted and more testing is sometimes needed to prove exactly where the restriction is, but you would be on your way to solving that symptom.