Knock acceptable while "cruising", how much?

[ManBearPig]

The cat deletes I have consist of a factory driver side header with straight pipe welded in place of the cat. The passenger side header hasn't been removed but Yes, I did have to remove the driver's side header and motor mount bracket. It was shortly after I did this that I noticed the knock. I was convinced this was the problem so I put the factory headers back on and noticed no difference. I'm now convinced that the car was doing this before, I just never noticed.

The springs have been on the car since the first week I bought the car but I really don't think they have anything to do with it. The knock occurs under the same conditions I would expect real knock would. Maybe I should try some torco. Vp octanium is what I used for octane booster but maybe it's not as good? I'm still not convinced the knock is false even though I do see it on the stock tune.

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[mustang1]

I would try with a can of Torco in the tank and see what your log look like. Not alarming numbers but could be better if it's real knock. The 1-1.25 could be from bad fuel and/or too much timing commanded in the tune.

Car is stock. Running 93 octane gas. And I think it was 65F that day. I really doubt that is real knock. As far as I can tell, car is running great.

 

[Oakley_5OH]

The cat deletes I have consist of a factory driver side header with straight pipe welded in place of the cat. The passenger side header hasn't been removed but Yes, I did have to remove the driver's side header and motor mount bracket. It was shortly after I did this that I noticed the knock. I was convinced this was the problem so I put the factory headers back on and noticed no difference. I'm now convinced that the car was doing this before, I just never noticed.

The springs have been on the car since the first week I bought the car.

And no other mods? No suspension or other performance mods? You just remove the motor mount bracket and NOT the motor mount itself, correct?

One of my theories is that it is the motor mounts or motor mount brackets. I did NOT remove the motor mounts, but I did remove the motor mount brackets on both sides.

Hear me out - If it only happens after shifting, the motor does not have any torque going through the drive train while shifting from one gear to another, so the motor is level. When you give it enough gas, the motor starts torquing upwards on the one side. Now, if I remember correctly, the driver side goes up when you rev the motor. Maybe when the motor was raised and put back down, the motor shifted either too much one way or the other and is now slightly tapping something on the header? Or one of the bolts are slightly loose, either the 3 or 4 bolts connecting the motor mount bracket to the engine or the top bolt connecting to the motor mount bracket to the motor mount?

I leave on a trip tomorrow morning until Monday, but I will be testing this theory out over Thanksgiving Day.

Thoughts? This is the only thing that I can think of that we both did with the exact same knock issue.

 

[ManBearPig]

And no other mods? No suspension or other performance mods? You just remove the motor mount bracket and NOT the motor mount itself, correct?

One of my theories is that it is the motor mounts or motor mount brackets. I did NOT remove the motor mounts, but I did remove the motor mount brackets on both sides.

Hear me out - If it only happens after shifting, the motor does not have any torque going through the drive train while shifting from one gear to another, so the motor is level. When you give it enough gas, the motor starts torquing upwards on the one side. Now, if I remember correctly, the driver side goes up when you rev the motor. Maybe when the motor was raised and put back down, the motor shifted either too much one way or the other and is now slightly tapping something on the header? Or one of the bolts are slightly loose, either the 3 or 4 bolts connecting the motor mount bracket to the engine or the top bolt connecting to the motor mount bracket to the motor mount?

I leave on a trip tomorrow morning until Monday, but I will be testing this theory out over Thanksgiving Day.

Thoughts? This is the only thing that I can think of that we both did with the exact same knock issue.

Correct, I removed the motor mount bracket, not the mount itself. And only the driver side. I totally agree with your thought process, but I have double checked every bolt I have ever touched at least 6 times. I am a thousand percent sure that nothing with the exhaust or motor mount bracket is loose or contacting any part of the car. I also didn't ever touch the passenger side mount so the motor couldn't have shifted much if at all.

But your theory about the motor moving and touching something is valid. I just can't find ANYTHING.


The car has steeda springs, irs bushing supports, tune, catback. Completely stock otherwise. Do you see the same knock activity on the stock tune?

 

[ManBearPig]

I don't remember if I mentioned this or not. I've spent several hours under the car tapping on things with a mallet. The MBRP mufflers do have a slight rattle so MBRP is sending me a new pair. Highly unlikely that is causing an issue but it's worth a shot. Banging on the exhaust does produce some odd resonance, not a satisfying thud. But I can't see it being an issue. I'm hopeful the replacement mufflers will help but certainly not holding my breathe.

 

[Oakley_5OH]

Correct, I removed the motor mount bracket, not the mount itself. And only the driver side. I totally agree with your thought process, but I have double checked every bolt I have ever touched at least 6 times. I am a thousand percent sure that nothing with the exhaust or motor mount bracket is loose or contacting any part of the car. I also didn't ever touch the passenger side mount so the motor couldn't have shifted much if at all.

But your theory about the motor moving and touching something is valid. I just can't find ANYTHING.


The car has steeda springs, irs bushing supports, tune, catback. Completely stock otherwise. Do you see the same knock activity on the stock tune?

Did you loosen up the passenger side at all before pushing the motor up to remove the motor mount bracket? Do you think the tension on the passenger side bolt loosened it? Have you checked the passenger side at all?

I have checked my bolts too. I have a lift in my garage thank god. But I am going to see if I can figure out which side has more room and possible move the motor over a tad. The 4 (I think it is 4?) bolts connecting the motor mount bracket to the motor and the one bolt on top of the motor mount bracket are the only bolts that we BOTH have touched if it has to do with the motor mount.

Obviously the cat back exhaust is easy enough to make sure it is not touching anything and the bolts are tight, so I am automatically assuming it does not have to do with the cat back.

I have Eibach Sportline Springs, UPR Vertical Links, Texas Speed Headers, Corsa Sport Cat Back (Originally had MBRP Cat Back), UPR Catch Can, AirAid Cold Air Intake, Shoemaker 93 Tune (completely new tune as of a month ago with him as well), Aftermarket Wheels, Mickey Thompson Tires, Mishimoto Coolant Tank, BMR Toe Links, Steeda IRS Braces, and I think that is it that has to do with performance/suspension.

 

[Oakley_5OH]

I don't remember if I mentioned this or not. I've spent several hours under the car tapping on things with a mallet. The MBRP mufflers do have a slight rattle so MBRP is sending me a new pair. Highly unlikely that is causing an issue but it's worth a shot. Banging on the exhaust does produce some odd resonance, not a satisfying thud. But I can't see it being an issue. I'm hopeful the replacement mufflers will help but certainly not holding my breathe.

I originally had a similar sound and thought it was the header pipes tapping each other. But I think it was one of the bolts loose. After having a third party re-tightening them, the sound went down. It is still a little bit of a sound, but nothing like before, and still knock.

 

[ManBearPig]

I never touched the passenger side mount. It's worth checking though I suppose.

I do have a ford Motorsport oil separator. Forgot to mention that. I considered taking it off but kan....I just can't see that being an issue.

In my experience with tuning carburetors on motorcycles, the transition from zero throttle to partial load is crucial and knock/ping can occur if something is off. I had a bike that would knock in this area unless I ran race gas because the base gasket was too thin and the compression was too high. Not apples to apples but my point is that this area of the throttle (tip in) is succeptible to knock. I'm not convinced what we're seeing is false. Just not sure why no one else sees it. Or maybe they do and just don't notice?

 

[Oakley_5OH]

I never touched the passenger side mount. It's worth checking though I suppose.

I do have a ford Motorsport oil separator. Forgot to mention that. I considered taking it off but kan....I just can't see that being an issue.

In my experience with tuning carburetors on motorcycles, the transition from zero throttle to partial load is crucial and knock/ping can occur if something is off. I had a bike that would knock in this area unless I ran race gas because the base gasket was too thin and the compression was too high. Not apples to apples but my point is that this area of the throttle (tip in) is succeptible to knock. I'm not convinced what we're seeing is false. Just not sure why no one else sees it. Or maybe they do and just don't notice?

I never saw any knock until I put my headers on, which is why I suspect it is false. Plus, it only happens once ever 5 or 6 times I switch gears and I could shift at the exact same RPM, from and to the same gears, etc. etc. (or at least very very close).

Yes, this could be happening to other people but if they do not have a tuner and do not have the knock sensors on the screen to monitor it, they wouldn't know. I can't even really tell when it happens because it is so intermittent and such a short period of time, it doesn't really impact how the car drives, surprisingly.

One of my buddies has suggested the possibility of a bad knock sensor or knock sensors. Which I highly doubt, since I haven't messed with the intake or anything close to the knock sensor or knock sensor connectors/wires.

 

[Oakley_5OH]

Did you put the oil separator on around the same time when you did the cat delete? I heard some people having the UPR catch can, the one hose has a check valve and it was banging off of the coolant expansion tank causing knock. I have taken mine off and drove it for a week without it and put it back on because the knock was still there.

 

[ManBearPig]

I've had my oil separator on for a long time. It's plastic and doesn't hang freely. But I'm down in the garage now so I took it off just so I can rule it out. It tends to collect about an ounce per thousand miles. Nothing too alarming.

I jet checked the upper motor mount bracket bolts on both sides and again checked the four under the car on the passenger side. All good there. Do you see knock on your stock tune?

 

[Oakley_5OH]

I've had my oil separator on for a long time. It's plastic and doesn't hang freely. But I'm down in the garage now so I took it off just so I can rule it out. It tends to collect about an ounce per thousand miles. Nothing too alarming.

I jet checked the upper motor mount bracket bolts on both sides and again checked the four under the car on the passenger side. All good there. Do you see knock on your stock tune?

What about the two bolts holding the motor mount? I know you said you didn't take them out, but might as well check if you are there lol

I have to check the stock tune. With the intake and everything, I think the car will just run like complete dog shit with the stock tune, but I don't think there is any harm in trying?

My car is currently on the lift with no wheels because they are getting powder coated while I am in Florida. I have a list of random stuff I just put down on my phone to try hahaha :frusty:

 

[ManBearPig]

Forgot you had an aftermarket intake. I wouldn't run that on the stock tune. Car probably won't even be driveable.

Underneath the car banging on the exhaust it just seems awfully rattly. Nothing is touching the body and no clamps are loose. I think most of the rattling noise is coming from the flex pipe on the passenger side in front of the catback joint. The cat delete pipes I had on previously did not have this flex pipe. And honestly when I banged on everything with those pipes it seemed a little rattly but not this bad. I guess the cats make a little noise too

The two bolts on the motor mount are tight. I have checked everything there is to check at least a dozen times. The only thing even halfway suspect is the exhaust rattle sound when I beat on it with my fist. I don't have another car to compare it to though.

 

[markmurfie]

Are these knock sensors designed to look for frequencies specific to spark knock or will anything else internal set them off? Rod knock, excessive valvetrin noise, etc?

Yes, a lot of filtering based on frequency.

5300 hertz for cylinder one below 3500 RPMS.
the other cylinders are 5900 hertz below 3500 RPMS
Above that its 6300 hertz, except cylinder 5 and 7 which are 5700 hertz.



video of what knock sounds like.

 

[ManBearPig]

I didn't realize the knock sensors were that specialized. Makes me question how often knock is really false. Seems awfully coincidental for a rattle in the exhaust to be picked up as matching a specific frequency that the sensors are looking for.

What are the chances a rattly exhaust could even cause false knock? Maybe I should try some proper race fuel instead of 93+ vp octanium

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