I recently put a custom tune on my truck. I love the tune, but I noticed a noise when starting up the truck when it was cold. I have the 5.4 3v and it goes into a high idle for about 10-15 seconds when the block is cold and then the idle goes down. Well when in that high idle, I hear a knocking noise which to me sounds like an exhaust leak and I'm sure it is louder on the passenger side. I also notice there is visible exhaust coming out the tail pipe during this same time period.

I'm wondering if it is an EGR issue. I'm pretty sure I've never heard this noise before. Oil pressure gauge shows good the entire time.

Also, I'm curious about the visible exhaust I can see. It is alot more visible during this fast idle/knocking period. Could this be an open loop period? I know the O2 has to warm up before the truck goes into closed loop, and I can't imagine an O2 can warm up in 10-15 seconds. My old GMC would take a few minutes I remember.

Anyway, any ideas? Thanks.

PS: On the weekend I returned the truck to stock computer and drove around a bunch. I started it a few times this weekend when it was cold and still got the same noise.

 

sounds like piston slap?

 

It's pretty loud for 10-15 seconds only.

Piston slap usually goes away once the piston heats up. I can't imagine my piston is heating up in 10-15 seconds. The outside temperature right now has been about 50 degrees F for the last few weeks since I noticed this noise.

 

with my old engine being cold, id have piston slap for about 4 seconds...

 

What makes you think it was piston slap?

 

It is a pretty common problem on these trucks. Try a search if you haven't already. This has been mentioned many times. By all accounts it is nothing to worry about.

 

Ya, I'm pretty familiar with the valve noise these trucks have. But this noise seems to be pretty recent.

 

What are you using for oil and oil filter? It sounds like it may be a dry start due to oil that's too heavy and/or an oil filter with no anti-drainback valve.

 

Actually, I just did an oil change and the noise was no different. The oil I use is AMS oil 0W20 with Ford filters.

 

Those are both fine.

 

Because I was starting to wonder if I'm crazy or not, I listened to a friends truck upon cold startup and his does not make the noise. So now I'm even more certain that it recently starting making this noise. I just wish it did it more often to help diagnose it. 15 seconds is a pretty small window to determine a problem.