Clunking/banging during first startup of day

[Flapjack]

Since it's gotten cold, my 2013 GT manual has started doing this on the first startup of the day. Once the car has been driven, it doesn't do it. But after sitting all night in the cold (even when parked in the garage), it's almost guaranteed it will surge and bang for about 10 seconds.

I got the car at 13k miles over the summer. I just hit 20k a few miles ago. The oil was changed at 13k miles, and the reminder light just came on yesterday... the clunking has been happening for a few weeks, though.

Any ideas?

 

[Flapjack]

I'm wondering if it has something to do with the cam phasers and low starting oil pressure. I know nothing about how the VCT on the 5.0L works, though...

 

[eighty6gt]

It's probably doing it because you're posting tech in chit chat!

 

[eighty6gt]

Sounds kind of like lean pops or misfires, I'd start looking at spark plugs and injectors.

 

[13726548]

I'm wondering if it has something to do with the cam phasers and low starting oil pressure. I know nothing about how the VCT on the 5.0L works, though...

At start up oil pressure will be higher than warm oil pressure. Pressure has an inverse relationship with flow. I haven't watched the video yet because work, but are you using an engine oil viscosity & oil filter per OEM recommendations? An oil filter with a silicone anti-drainback valve (Motorcraft) will help prevent dry starts.

 

[Flapjack]

Sounds kind of like lean pops or misfires, I'd start looking at spark plugs and injectors.

I suppose it could be... but that's not what I typically associate with a "misfire" sound. Misfires aren't even normally audible, and they usually trigger a CEL. I'll check to see if there are any codes tonight.

At start up oil pressure will be higher than warm oil pressure. Pressure has an inverse relationship with flow. I haven't watched the video yet because work, but are you using an engine oil viscosity & oil filter per OEM recommendations? An oil filter with a silicone anti-drainback valve (Motorcraft) will help prevent dry starts.

That is not my experience at all. I have a real oil pressure gauge on my 05 (not a yes/no gauge like stock) and there is little-to-no oil pressure for the first few seconds until the oil pump primes. You are referring to Bernouilli's principle, and yes... where pressure is high, flow is low... but that relates to a container that is full. The higher the engine RPMs are, the higher the oil pressure is.

The car is bone stock (minus an aftermarket stereo). It has only ever been serviced by Ford dealerships, so I am 99.9% sure it has a motorcraft filter and whatever oil Ford uses (synthetic blend, I believe).

My bet is on cam phasers. The 3v have been known to fail, but that is typically with high mileage. Once RPM builds and oil pressure is established, the sound typically goes away. This engine only has 20k miles, though.

The other thing it could be is some sort of backfire... and it could be the exhaust system "jumping" as a result.

 

[13726548]

I do realize oil takes a few seconds to reach the valvetrain and pressure is supposed to rise with RPM. I was just pointing out the relationship between temp and pressure.
I have not done this personally but I know you can log phaser activity and compare the commanded cam retard/advance versus actual position. If there is a gap between the two, you know the phasers are bad.

 

[Flapjack]

I do realize oil takes a few seconds to reach the valvetrain and pressure is supposed to rise with RPM. I was just pointing out the relationship between temp and pressure.
I have not done this personally but I know you can log phaser activity and compare the commanded cam retard/advance versus actual position. If there is a gap between the two, you know the phasers are bad.

Yes, pressure does go down when flow increases due to the change in temp. It's even more prevalent with 10W-30 oil (vs 5W-30). I may change to 5W-30 with this oil change and see if the sound goes away.

 

[eighty6gt]

I hear it as misfire/backfire/lean pops because that's exactly what they sound like on my motorcycle engines.

Goes away when the engine warms up because you're not as lean. Maybe you have a vac leak somewhere, I hope it's not the valvetrain.

 

[13726548]

Yes, pressure does go down when flow increases due to the change in temp. It's even more prevalent with 10W-30 oil (vs 5W-30). I may change to 5W-30 with this oil change and see if the sound goes away.

It is good to use the lowest viscosity oil that still maintains hot idle oil pressure.

I hear it as misfire/backfire/lean pops because that's exactly what they sound like on my motorcycle engines.

Goes away when the engine warms up because you're not as lean. Maybe you have a vac leak somewhere, I hope it's not the valvetrain.

I may be completely off base but the mixture is rich at start up and maintains stoich once it goes to closed loop. I do agree that it sounds like exhaust backfire (which could be caused by misfires in the ignition) so I would look there first.

 

[eighty6gt]

Yes of course it is rich at start up, except when there's a vac leak or plugged injector and it's causing a lean issue. Once the fuel stops condensing on the cylinder walls and in the intake your issue isn't as bad for the engine. Still there.