Car Background: 2008 Bullitt, around 72,000 miles, daily driven, not driven hard excessively. I always put premium 91 gas (I'm in California, it's all we got) from either Chevron or Costco, occasionally from a different gas station. The

My car has been having a thud/knocking sound recently. I took it to my mechanic and he said it was the blow by hose. I had bought it used and didn't realize it, but apparently the car had the wrong hose on there. Kinda looked like a radiator hose was cut and clamped in so it would collapse. It was changed to the proper hose but there's still the knock/thud. I had a coworker listen to it and he said it might be a sticking valve from the sound and quite possibly the intake valve. Has anyone ever run into this issue before? What's the fix? The sound only comes during idle, it's not constant.

 

I would find a sticking valve to be extreme. Does it miss at idle? Does it stutter when you take it to redline? Why would your friend guess an intake valve? Besides, the 4.6L is a free wheeling engine - the valve doesn't interfere with the piston at TDC for there to be a 'thud'.

You could try some upper cylinder cleaner/lubricant like Regane if you want to run some cleaner through the system. I have used it for years on my old F150 when its running rough and one tank cleans it right up. Though I have never had a 'knock'.

This thread has some ideas for ticking sound if that's what you are describing:

https://themustangsource.com/f637/4-...2/#post6812055

 

The sound only occurs at idle. It's not constant, just happens sometimes.

I'll check out the threw and see if that helps. Thanks!