the dreaded engine knock. at high RPM, especially above 5k in 2nd and at any point in 3rd under WOT i was getting knocking with 87octane. this time around i filled up with 89o ctane, and so far no knocking. anybody else experiencing similar?

 

I experienced same issue but only when I used Citgo 87 octane gas. I switched to Mobil 87 octane, no problem

 

Sorry...know it's an old post, but didn't feel it necessary to create a new one.

I took my car to the dealership to locate a slight ticking sound I thought was coming from the left front of the engine compartment (thought it may be the missing bolts in the heat shield issue...no bolts were missing).

Their diagnosis = "spark knock"
Solution = "use premium" (92 octane) instead of the suggested 87 octane

The knock went away, but after reading this post, I think I'll try 89 octane and see what happens. I've already got 12,000 miles, so if serious damage could be caused by this, it's probably already been done.[&o]
I've only got a 36,000 mile warranty, and I drive about 4,000 miles per month. I'm guessing that since I had the issue diagnosed while under warranty, if something happens later on as a result of this it should be fixed under warranty...? I hope that day never comes.

 

Retarding the timing (requires tune) will cure this. Different elevations create different fuel requirements. Also opening the plug gap slightly does the same exact thing as retarding timing. Try gapping up a couple thousands. May save you $$$ on gas (meaning premium vs. regular) and is a simple fix. Again, elevation and humididty affect air fuel ratio. P.S. closing the plug gap will increase timing a couple of degrees if anyone was considering bumping up the factory timing without a tune.

 

Thanks for the plug gap info. I'll mention it to my service tech.
After I posted that the ticking went away, I heard it again. It's not all the time anymore, but it still happens every now and then. Since it sounds like the front left of the engine bay, one plug being gapped improperly or just defective would make sense. Thanks again!

 

Something else to consider if you notice the sound (spark knock) coming from the same area/cylinder. Fords are notorious for typcially having one or two cylinders in a V6 or V8 that get hotter than the rest of the block. This is due to their block and intake design and the placement of the back two cylinders right up against the engine bay where they get heat build up.
3.8L Mustang engines in the 99-04 are notorious for having a Spark knock at moderate or heavy loads on the drivers side cylinder closest to the firewall.

Several remedies can be used to 'fix' this. One was already suggested (spark plug gap)
Increase octane of fuel used
On older engines if just appears out of nowhere, decarbonize the engine
Get a colder plug(s) for the cylinder(s) closest to teh firewall on the driver side (where the knock usually occurs)
Mess with the timing

Not certain if it will solve it for you on the 05/06 model but those worked well on the 99-04 models