I got a F150 with a 5.4L and when I'm cruising down the highway every is goin well until I start to pull a hill. A loud fast rattle starts coming from the engine compartment, it sounds like it is mainly coming from the drivers side. The noise is really evident just before the truck down shifts out of OD, then its not as noisy and goes away when the truck is at full speed and not pulling a hill. The truck has lots of power and there are no check engine or fault lights on at all. The truck never hesitates. Interesting note, it doesn't make the rattle when revving the truck up in neutral. I really have no idea on this one and it is really starting to annoy the heck out of me when driving. Any ideas would be helpful me dearly. Thanks guys!

 

Sounds like detonation, have you tried a tank of hi-test?

 

Whats Hi-test? If it was detention wouldn't there be a check engine light??

 

Do you mean Premium Fuel?? If so, No I have not. I've been running 87 octane.

 

you might look at the pcv valve i hurd a crazy sound coming from my engine and i started moving stuff and found that one of the pcv valves were either stuck or loose, either way it was bad i found an old one i had laying around, threw it in and havnt hurd it sense. the sound got louder as the engine reved up so hopefully this helps, the valves are located on both valve covers towards the back.

 

X2 on pinging or aka pre detonation as stated try some higher octane fuel and you should be good to go..

 

I'd agree on ping too, mine has never thrown a code from it.

 

Mine did a similar thing, sounded like pinging, when moderate throttle pulling a hill for instance. Also had the idle knock. Got cam phasers changed noise gone. About 75000 miles.

 

Sweetrocks is your truck 4X4?

 

Yea you bet my truck is a 4x4. I tried a higher octane fuel and It didn't clear up. Could using 5w-30 syn instead of 5W-20 be messing with the phasers ?? I run 5w-30 in all my company ford trucks and don't have these noise?? What do you guys think?

 

I suspect phasers. What is your miles on the engine??

 

72000Km, Truck got new phasers at 36000Km that were suppose to be the new generation phaser.

 

Was any work done on the timing chain?? I have read where the tensioners on some of these fall apart and the chain rattles. I am no mechanic. Just throwing out ideas.

 

I'd think it would be rattling all the time, not just at load if that were the case.

 

I experience similar rattling. Thought at 1st was piece of loose sheet metal vibrating. No grinding. Doesn't sound like detonation/ octane rattle, had tried higher octane gas, that didn't seem to make a difference. Crawled underneath last night cant see anything loose. Was looking for broken spotwelds on exhaust heat shields. Noise is definitely from cab forward. Noise appears at approx 40mph with slight throttle pressure where load increases up to point of downshifting transmission. Normal driving- no noise, no vibration. Cruising 55+- no noise. When it make the noise, you can depress brakes and it makes no difference. Vibration frequency not proportional to RPM. Any clues?