Cold start knock

[4OYOTER]

I have recently noticed a knocking sound on cold starts only that almost sounds like it's coming from the driver floorboard or firewall area. It only happens when I'm in gear and on the brake and my RPMs drop. I will hear it as soon as I go into reverse to back out of my driveway. Then when I hold the brakes as I shift into drive the noise continues. Once I start driving I can't hear it unless I come to a stop while the engine is still cold. Any ideas?

This is in my 4.7 with 118K

 

[ctduncan]

Interesting, I just got the exact same thing a couple of days ago for the first time. I have the 4.7l @ 117,000 miles. Any info would be appreciated.

 

[tysauce]

Search for fuel pulsation dampener - see if that helps!


Sent from my iPhone using Tapatalk

 

[skott]

I'd guess it's piston slap. My 2006 with 215K miles has been doing this when it's cold since the day I've owned it. Only when cold and only when engine is under any sort of load (ie, in drive with foot on brake). From everything I've read, it's a non-issue and the fact my engine runs perfect and doesn't burn a drop of oil, I'd have to agree.

I can't explain why you've never heard the noise before, though. I would have imagined the sound would have always been there. Piston slap isn't something that "just happens". Others say it's a fuel pressure regulator thingy, (like the previous poster), so try checking into that.

 

[Silver_midlife_t4r]

I've got the same noise from my 2005 V8 4.7 with 140k. I first noticed it as fall/winter came on (temps in the low 50s F). It goes away as soon as the rpms are above 1000.