PitCritter

Recently, I've had a problem with engine knock. It was very minor until I filled up with what must have been a bad batch of Shell regular grade. After that, it's gotten much worse.

The engine rattles terribly under even minor load at around 1200-1800 RPM. For instance, if I'm on cruise at 60 and I come up on a minor hill, I can count on hearing engine knock. Now, when i see a hill coming, I downshift to keep the revs up and all is fine.

I've run a full tank of premium grade through it and two bottles of Seafoam in a tank of midgrade. It's now better but not perfect.

There are no codes generated.

I wonder if I might have a bad plug or coil but I thought I'd ask here first before blindly pulling things apart.

Thanks for any and all replies.

AITG

Try running Techron through it. Follow the directions on the bottle and see what happens. As long as you have no codes, that may work.

PitCritter

OK here's an answer I never expected

When I started the truck the other morning, the battery light came on.

It turned out that my alternator had died.

After I replaced it, the knock was completely gone.

It seems that i wasn't getting enough electricity produced at low RPMs for thorough combustion.

One way or another it's fixed.

PitCritter

First, thank you to everyone here for not saying what you were thinking..."this guy's nuts".

Turns out you would have been right.

After telling my mechanic this story, HE told me I was nuts and immediately told me exactly what the problem was.

The knock was the reason my alternator died, sort of. Turns out it wasn't engine knock at all. I had a bad belt tensioner that killed my alternator. The sound went away when I replaced the alternator due to less load on the belt system because of brand new bearings in the new alternator.

I should have realized it wasn't knock since there was no hesitation or loss of power, only the sound. Although the sound was exactly what I've heard as knock in the past.

One way or another, it's NOW fixed. I wonder how much damage I've done to the new alternator. Thank God for lifetime warranties.

PitCritter

Update, not fixed.

Now it's back and it looks like my timing chain is shot. Not the answer I was looking for.

standfast85

Terrible news.

Keep us updated, please.

bm4183

Any updates?

My 2011 5.0 with 140,000 miles is doing the same thing exactly as you described. It stopped for a few months when I did the fuse 27 repair, but the rattle/knock returned. Do you think it could be related to the fuse or a fuel pump issue?