Intermittent clunk on startup
Thread Starter
Junior Member
Joined: Jan 2020
Posts: 13
Likes: 1
Intermittent clunk on startup
Hello everyone,
I have a 4x4 2008 F-150 with the FFV 5.4. Recently I noticed a single clunk upon startup that sounds like a knock coming from behind the passenger dash or under the passenger floor. I don't feel any hard vibration when this happens and the drivability of the vehicle has not changed so I'm inclined to think it wouldn't be something heavy clunking in the drivetrain. I've cycled the transfer case from 2WD to 4WD several times both in gear and out of gear, no clunk from that so I don't think it's transfer case related. I know it isn't the A/C clutch because it happens regardless of the compressor being engaged. To be clear, this clunk happens only once as soon as the engine fires, not while cranking, and then there is no noise after.
As far as it being intermittent, I haven't pinned down any consistent patterns but I have noticed that it will only happen during cold starts if the truck has sat for a day or two. It has never happened when the engine is warm or above ambient temp (currently anywhere from 75-90 F). Other than the noise itself, I haven't noticed any changes to the vehicle's driving characteristics so I'm a little stumped.
Any thoughts or suggestions would be welcome!
I have a 4x4 2008 F-150 with the FFV 5.4. Recently I noticed a single clunk upon startup that sounds like a knock coming from behind the passenger dash or under the passenger floor. I don't feel any hard vibration when this happens and the drivability of the vehicle has not changed so I'm inclined to think it wouldn't be something heavy clunking in the drivetrain. I've cycled the transfer case from 2WD to 4WD several times both in gear and out of gear, no clunk from that so I don't think it's transfer case related. I know it isn't the A/C clutch because it happens regardless of the compressor being engaged. To be clear, this clunk happens only once as soon as the engine fires, not while cranking, and then there is no noise after.
As far as it being intermittent, I haven't pinned down any consistent patterns but I have noticed that it will only happen during cold starts if the truck has sat for a day or two. It has never happened when the engine is warm or above ambient temp (currently anywhere from 75-90 F). Other than the noise itself, I haven't noticed any changes to the vehicle's driving characteristics so I'm a little stumped.
Any thoughts or suggestions would be welcome!
5 Year Member
Joined: Dec 2018
Posts: 4,436
Likes: 1,186
From: Ocean Springs MS
"Any thoughts or suggestions would be welcome!"
Grab ahold of the starter motor and see if it is loose. Wiggle it as hard as you can.
Flex plate on some fords have been known to crack (or become loose) and cause sort of a bang on startup
Both of these possible causes are pretty easy to check but its hard to imagine that they are temperature related
Jimboy
Grab ahold of the starter motor and see if it is loose. Wiggle it as hard as you can.
Flex plate on some fords have been known to crack (or become loose) and cause sort of a bang on startup
Both of these possible causes are pretty easy to check but its hard to imagine that they are temperature related
Jimboy
Thread Starter
Junior Member
Joined: Jan 2020
Posts: 13
Likes: 1
Jimboy,
You'll never believe this, but I just figured out what it was a few weeks ago. I need to get my ears checked because it wasn't a clunk at all. When I started it once, I was lucky enough to see the hood jump downwards very slightly at the exact same time I heard the "clunk". Upon further investigation, I found a long, thin piece of black cloth tangled up in my engine bay, and that's when I noticed several large parts of the hood liner were shredded and hanging down right next to the serpentine belt / fan shroud. Evidently the noise I was hearing upon startup was the engine violently ripping pieces off the hood liner. I've since removed the low hanging parts and secured the remainder of the liner and have not heard the noise once in the past few weeks that it's been fixed. I think the whole deal with it being only on a cold startup was unrelated, and had just been by chance as this hadn't been going on for very long before I made the original post.
As per the suggestions, I checked the motor mounts and starter just to be safe (it is an older vehicle so no harm in checking) and found them to be secure. I also made sure there was no damage to the fan or belt, and checked for any remaining shreds of the hood liner that might still be embedded in the engine bay somewhere. I did a little research about the flex plate and I didn't feel like that was consistent with what I was experiencing, so while I didn't completely rule it out, I felt it was not likely to be the issue.
- Blueshift
You'll never believe this, but I just figured out what it was a few weeks ago. I need to get my ears checked because it wasn't a clunk at all. When I started it once, I was lucky enough to see the hood jump downwards very slightly at the exact same time I heard the "clunk". Upon further investigation, I found a long, thin piece of black cloth tangled up in my engine bay, and that's when I noticed several large parts of the hood liner were shredded and hanging down right next to the serpentine belt / fan shroud. Evidently the noise I was hearing upon startup was the engine violently ripping pieces off the hood liner. I've since removed the low hanging parts and secured the remainder of the liner and have not heard the noise once in the past few weeks that it's been fixed. I think the whole deal with it being only on a cold startup was unrelated, and had just been by chance as this hadn't been going on for very long before I made the original post.
As per the suggestions, I checked the motor mounts and starter just to be safe (it is an older vehicle so no harm in checking) and found them to be secure. I also made sure there was no damage to the fan or belt, and checked for any remaining shreds of the hood liner that might still be embedded in the engine bay somewhere. I did a little research about the flex plate and I didn't feel like that was consistent with what I was experiencing, so while I didn't completely rule it out, I felt it was not likely to be the issue.
- Blueshift
5 Year Member
Joined: Dec 2018
Posts: 4,436
Likes: 1,186
From: Ocean Springs MS
Blueshift,
Thanks for getting back to us. Now just think if someone had suggested that you check the hood liner for shreds of cloth, that would have gotten a lot of people laughing.
Jimboy
Thanks for getting back to us. Now just think if someone had suggested that you check the hood liner for shreds of cloth, that would have gotten a lot of people laughing.
Jimboy
