Okay, so to start, I have a 2016 XLT SCrew.

Relevant mods are:

AFE Off-Road (Catless) DP
SCT Livewire TS+
Borla ATAK Catback
QTP Exhaust Cutout
Snow Water/Meth Kit w/ 7 Gallon Tank in bed toolbox (70M/30W mix)
K&N CAI
New Motorcraft (week old) plugs gapped to 0.28 with feeler gauges

The Borla ATAK system was WAY too loud once I added the DP. I then welded in a Borla ProXS muffler in the same spot as in their S-Type system. It was then too quiet, like stock with a bit of turbo whistle. Finally I welded the wireless remote control QTP cutout between the resonator and muffler and got exactly the awesome insane sound I wanted at the push of a button that I didn't have to listen to all day.

I am running MPT tunes, specifically their 93PRX for Water/Meth and have gone through a few revisions via data logging. Just yesterday with the final review Mike from MPT said "Wow, those logs look great, no adjustments needed" with a few stop launches and a few third gear pulls up to red line.

So, I think great, I'll get off work, change the oil as I beat on it the last 3-4k miles doing a road rally, hitting the drag strip, etc. I previously had Pennzoil Platinum 5w-30, and a Mobil 1 filter. I changed it with the same Pennzoil, but this time used a Fram Premium Synthetic filter like an idiot because I was already at Walmart and too lazy to go anywhere else.

I then drive to the auto parts store, get a Motorcraft filter, and a QT of oil. I quickly spin the Fram filter off, spin the Motorcraft on, start the engine, turn it off, let it settle, check the dip stick, and add the oil lost to the filter change.

I go for a drive, shockingly the same thing.

My Knock Rating readings have been pretty standard. Up to about 3 running a tune when in a higher gear, under part throttle. 1 to 2 at most under part throttle with the stock tune. I have never, EVER had any physical indication of knock. No pinging noises, no engine stumbling, nothing. Every so often I would see a spike up to 7 degrees maybe once a week. I always chalked it up to phantom knock or a vibration.

Right after the oil change I got for a drive, and I noticed my Knock Readings are going crazy. On the MPT tune it was spiking up to 9.5 taking off from a red light at normal city driving habits. It would hit 4-6 and hold steady until a shift and then nose dive to zero. Sometimes it would go into the negatives, which is great. I have a hard time believing this is real knock because again no signs, and for it to go so high at one red light and into the negatives at another, I just don't buy it.

My truck runs 93 from usually Shell or BP. It has for the last 30+ tanks of gas.

So, I set it back to the stock tune, and go for a drive. The stock tune reads the Knock Sensor up to 6 degrees. Again, I am pegging the Knock Sensor at 5.99 degrees.

I get on the freeway near my house, and give it some part throttle at freeway speeds, nothing. In fact, once boost goes positive KR starts reading negative.

At this point the knock sensor reading in city driving is so bad it is causing my Octane Adjust Ratio to take a massive crap. I was sitting happy at -0.98 and now am up to +0.28 because of this phantom knock.

So, here is what makes me believe it is false knock:

1. No signs of real knock. No pinging. No engine stumbling.

2. WOT with the water/meth tune or stock tune quickly nose dives the knock reading into the negatives and holds steady

3. Great performance with no knock until after the oil change last night. I am 99% positive what I put in was 5w-30 Pennzoil Platinum from Walmart. Never had an issue before with the stuff and I hear it is great oil.

4. My water meth kit is progressive, with dual nozzles. I have one tiny 60 ml/min nozzle. Even if I set this nozzle to activate at 1lb of boost to try and retard any "knock" occurring there is zero difference.

5. The readings are mainly between 1600-2200 RPM leaving red lights where things would tend to get "vibratey"

I am at a loss at this point. Something has to be vibrating or making a specific frequency of noise to cause the Knock Sensor to read like it is.

Here is my plan of action for tonight once I get it in the shop and on the lift, if anyone has any other recommendations I'd love to hear them.

1. Hook up my buddies Snap-On scanner, run it in Mode 6, and go for a drive. For false knock I would expect to see it across multiple cylinders, or at least more than one. I also expect to see little to no misfire data.

2. Check exhaust for leaks, weld cracks, and tighten everything up from the turbo flanges back as it has been about 2,500 miles since it was finished. Also check Heat Shields for rattling.

3. Thoroughly check engine bay for tools I may have left that could be knocking around and causing false readings. Also double check all wiring and any aftermarket component like HID ballasts to make sure everything is mounted securely and rattle free.

4. Take my inspection camera and scope the engine cylinder valley to make sure nothing is hanging out in there. Road debris, an acorn from a squirrel, a missing socket, etc.

 

Could it be the butterfly valve on the cutout vibrating? I tend to agree it is probably something vibrating and being picked up as knock. I would check the whole exhaust over first.

 

Good idea, thanks. It is going on the lift in about fifteen minutes to check everything over. I can even take the cutoff valve off and go for a drive to see if there is any change. I didn't even think of the butterfly loosening up and getting play. It seals pretty right but I will definitely check.

 

First put chassis ears on the block and wear the headphones while driving around and verify it isn't really knocking.

 

We did, and it is not. What you can hear however is a LOT of hollow sounding "resonance" or growl from the catless downpipe. This is not too surprising considering the loudest modification I made was removing the cats. Even louder than adding an exhaust. The Borla ATAK is straight through piping. Even the resonator section is just a piece of exhaust piping they burned a single hole in with a torch, slotted through the resonator can, and welded on either end.

So to update, I did find some wear marks where the resonator was hitting the body up top above it. To fix this we used high temp 3M epoxy and high temp rubber on top of the resonator after prying it down with a pry bar a bit.

Afterwards I re-tuned the vehicle and it definitely helped the false readings leaving red lights before getting up to speed. I didn't see anything over 4 or so, and my Octane Adjust Ratio is back down to -0.86 already. The "constant" false knock is much better.

The bad news, is there is still something that when it hits a certain frequency just right, is pegging the sensor. It will happen at one light, I'll hit the record button on my Livewire, and it won't happen again for the entire drive. Just before typing this I saw leaving a light manual shifting and taking it up pretty high RPM in first gear peg the knock sensor to 11.45 with the added range of the tune.

If I was actually getting enough knock to pull 11.45 degrees of timing I likely would have ventilated my block a long time ago.

Which brings me to my next question.

Does anyone know what frequency the Ford knock sensors operate on?

At this point I am ready to get sciency on this mf'er and come up with a real solution to the false knock readings that I know a lot of people are having after researching multiple forums.

I know the OEM EB catted downpipe has the "maracas" welded onto them. Anyone who has taken their OEM downpipe off knows what I mean.

The only thing I can figure these are for, are vibration dampening. I have not seen anything like those on the market anywhere, but I do know there are vibration dampeners for a certain frequency range available. At this point I am ready to try adding those in the same location as the OEM maracas on the downpipe.

 

Just drove it with my own Chassis Ears clamped to an un-used bolt boss on the front of the block, nothing other than valvetrain noise, and no noticeable new sounds or changes when the knock registers.

Quick sanity check though for something I found. The very front black carpet piece is loose. Not the one you take down for an oil change, but the one between the suspension crossmember and the silver small skid in the very front. I am curious if anyone else is able to push this up about two inches and let it fall knocking around. I can on mine and it if I push it up about two inches and let it come back down it does make a pretty loud rattling knocking noise.

If anyone would be so kind as to reach an arm under the front of their truck I would greatly appreciate it. I am thinking during an oil change the lube monkies touched the wrong piece of carpet on accident and then left it loose.

I can't get it off the ground to really check it out until tomorrow.

 

Its you downpipe resonating. Unfortunately it is considered a false knock and will pull timing, but the good news it wonèt cause any harm. I have gone through the very same issue with every turbo car and truck I have owned. I swore I would never run catless DPs again. My last car was really easy to swap the DP out and I was able to trace it back, if you had access to a proper shop is the only way I would want to swap the truck cats back in because they are a pita. But if you could try it and do some new logs to verify.

Other option is slowly reverse the easy mods you have done until you can find by process of elimination.