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Discussion Starter · #1 ·
I've had a trashed and torn upper motor mount on my driver's side for several months (at least). As time progressed I started getting strange sounds, squeeking rotors, tapping noises and bangs that all seemed to be associated with turning, breaking, accelerating. But nothing was consistent enough to be able to tell what was causing it. I thought I had bad suspension... A warped rotor lead me to think I had a bent wheel hub... a tapping sound made me think something was loose under the car... It drove me nuts for a long time.

In the back of my mind I thought there might be a slight chance that it was the motor mount but every time I pused on it, jumped on the car, rocked it back and fourth... nothing, no sound, zilch, nada... So I would start thinking it was somethign else....

ALWAYS TRUST YOUR GUT and remember that a lot (A LOT) of strange things can happen to your car if the motor isn't fastened nice and tight in there...

I replaced the mount today and instantly it's like I'm driving a brand new car. Quiet, smooth, no squeeking, smoother acceleration. It was like a miracle drug in the form of aluminum and rubber.

Just thought I'd share.
:bandit:
 

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BlueTT
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yah

haha i had the same sort of thing happen to me, for the life me me i couldn't find out wtf was makin the sound untill it finally dawned on me to check the motor mount, and that made my baby feel brand new again
 

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nice stang

yes nice Steeda Stang...MRbojangles do you even own a 3k/Stealth?

Btw, motor mounts are not supposed to give any horse power right? Well a friend of mine put new nice ones on his Scooby Wrx and i swear it had more power afterwards...Better acceleration and morre turbo push it seemed
 

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Discussion Starter · #5 ·
1sexy

I notice much SMOOTHER acceleration. It's possible that you DO actually have more horsepower because if they're worn out enough there is a possibility that your knock sensor is being triggerd by peices of metal banging together, thus retarding your timing.
 

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It won't give more horsepower, it will use what horsepower you have more efficiently. Just like a flywheel or clutch or lighter wheels, securing the motor in place helps transmit power to the wheels.

Good story, thanks for the heads up.

BTW. I'm not so sure about that comment about knock sensors hearing metal clicking together and thus retarding the timing. In fact I'm pretty sure that's totally off. The stock ECU wouldn't readjust fuel settings or timing just because it hears clanking, otherwise it'd be happening all the time. For example when you go over a hard bump, things rattle, but the timing isn't changed.
 

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Discussion Starter · #7 ·
3kluv

So basically what you're saying is that if your timing is being retarded you have just as much horsepower coming out of the engine as if it's not being retarded?

Please explain.

PS... When your motor mounts are worn, the knocking sounds and tapping that your engine experiences are COMPLETELY different from what it experiences by going over a bump on fresh motor mounts.
 

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clayperez,

What I'm saying is that there is zero correlation between loose motor mounts and a timing retard. The ECU wouldn't change anything because it doesn't have any reason to believe that a metal clanking is the engine phenomena "knock". And even if it did somehow recognize knock, it still wouldn't retard the timing. So what I'm trying to say is, no, loose or tight mounts won't do a thing to timing.
 

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Discussion Starter · #10 ·
3kluv

And even if it did somehow recognize knock, it still wouldn't retard the timing
Isn't knock was causes the ECU to retard timing? Unless you can prove to me otherwise, that is what I'm lead to believe by all basic knowledge of engine management that I've stumbled across.

Doesn't a knock sensor pick up vibrations caused by detonation? (yes?) Is there any remote possibility that this vibration can be closely mimmicked by metal-on-metal collision caused by badly worn mounts? (yes?)... Again, by reasoning I have come to this conclusion.

Do you have your own reasoning that disproves these conclusions?
 

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Yes, and I'll tell you exactly why.

During the tuning process after we installed the 17G's on the car, we were experiencing knock. The sums were around 5, but sometimes a little higher. According to your reasoning, the stock ECU would have retarded the timing due to the said knock. Since that didn't happen, I'm lead to believe that the stock ECU does not change the engine timing. That is something you get to do for yourself.

I'm also assuming that detonation doesn't sound anything like metal clanking, but I guess that's up to interpretation. All I know is that metal clanking will not trick the ECU into changing timing even if it sounds like knock, and even if the ECU changes the timing in the first place.

Have you ever tuned your ECU? Have you ever read off a pocket logger to figure out what was wrong with the car and why? Have you ever had to make your car stop knocking? I only ask because this whole thing about the ECU automatically retarding or advancing the timing is totally new to me and upon first glance seems a little incorrect. I would consider myself pretty educated about knock, and I've never heard of our ECU correcting it automatically. Sorry.
 

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The ECU absolutely pulls timing back to counter knock. Think of it this way; why would the manufacturer go to the trouble and expense of hooking up a knock sensor and keeping a running knock sum if it were not going to be used?

A knock sum of 5 is quite low - the ECU may not retard timing until the knock sum is higher. My car's a '94 so I've never been able to monitor the knock sum on the stock ECU...perhaps some of the 1st gens can comment?

- Brian
 

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I have a first gen and have experienced only slight knock. Maybe this is why I've never seen the timing retard. I was unaware that feature even existed.

But the point still stands, would the knock sensor get confused by worn engine mounts making noise? Doubtful.
 

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What you describe - false knock - I've seen discussed on the board a couple of times. I haven't seen it in my car, but the general consensus is that is a real phenomenon.

The knock sensor is just a microphone that picks up vibrations in the block. When knock occurs, it sends sound waves through the block. If vibrations equal to or greater than real knock are created by rubbing or banging of metal parts, the ECU has no way to distinguish these noises from actual knock.

The procedure I've heard for testing the knock sensor is to put a metal pole on the block, and hit the pole with a hammer. 'Nuf said.

- Brian
 

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FWombat said:
What you describe - false knock - I've seen discussed on the board a couple of times. I haven't seen it in my car, but the general consensus is that is a real phenomenon.

The knock sensor is just a microphone that picks up vibrations in the block. When knock occurs, it sends sound waves through the block. If vibrations equal to or greater than real knock are created by rubbing or banging of metal parts, the ECU has no way to distinguish these noises from actual knock.

The procedure I've heard for testing the knock sensor is to put a metal pole on the block, and hit the pole with a hammer. 'Nuf said.

- Brian
Its not a microphone, but still, it detects knock.

A bad motor mount causes the engine to have excessive movement thus hitting the subframe or usually the two metal pieces of the broken mount. And that hammer thing, a perfect test to check the timing retarda to see if the sensor is working correctly.


And stiffer mounts will increase idle vibrations but will allow for better lauches and less drivetrain fatigue.
 

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Yes, it is a microphone. It is a piezoelectric device, which is a type of microphone. Really.
 

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Would a device that has to pieces that rub together to create electricity be considered a microphone? Its not made to pick-up "sound" per se, but to notice vibrations caused by objects hitting each other.

It depends on your definitionof microphone and sound.
 

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moparacker said:
Would a device that has to pieces that rub together to create electricity be considered a microphone? Its not made to pick-up "sound" per se, but to notice vibrations caused by objects hitting each other.

It depends on your definitionof microphone and sound.
Dude, it's a microphone. I promise. If you wanted to, you could hook up the knock sensor lead to a tape recorder and record it.

Sound is nothing more than just good old vibrations. When you hear sound, the chain of events goes like this:
- The "source" of the sound vibrates for some reason.
- The source's vibrations compress and decompress air molecules, creating pressure waves in the air, aka sound waves.
- These air pressure oscillations cause your ear drums to vibrate.
- Your brain interprets the vibration of your ear drum as a "sound". (I'm admittedly fuzzy on the physiological stuff).

Microphones (including knock sensors, telephones, etc) work the same way. When the vibrations reach the microphone's "ear drum", a voltage is generated. This voltage is later interpreted by something (our ECU, for example). Alternately, the voltage might be amplified, altered, or recorded and forwared to speakers.

Our knock sensor is engineered to be sensitive to the types of noise generated by knock, and attached directly to the block so that it is very sensitive to vibrations in the engine, but at the end of the day it is a microphone.

- Brian
 

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Dude, calm down. I understand basic physics. A vibration isn't a sound if nothing can hear it. Its like "square = rectangle but rectangle �‚ square". Know where i'm going?

Its like this, you foot can notice vibrations. Does that make your foot a microphone? No. See where I am going.

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I just did some double checking before I posted how a quartz knock sensor works and found out there are quartz microphones. Figures. I only thought they had the diaphragm ones with magnetic coils and what not. And I knew thats not what is mounted to a engine block.

Oh well, I enjoyed it.
 
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