Need Help Diagnosing Knocking Noise

Cr-48

New Member
Nov 21, 2012
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I need some help diagnosing a knocking noise from from motor, because I have no idea where to start. My car is a '97 with about 125,000 miles on it. There are two codes from the ECU, P1131 and P1151, which indicate lean readings from the upstream O2 sensors.

About two weeks ago I noticed my car started running rough when stopped at lights, there was a low rumbling/knocking noise and vibration. This would stop as soon as I shifted it to neutral, reverse, or park. The noise and vibration would also stop as soon as I let off the brake.

Around the same time, I accelerated pretty hard (~3k RPM) and heard a terrible knocking/clunking/bearing rattle noise and the car had very little power. I haven't pushed it that hard since then, but I can hear the noise starting when I get up past 2k RPM.

The problem has gotten worse, shifting it out of gear no longer stops the noise all the time. I can hear the noise now when accelerating from a stop and even cruising at around 1-1.5K RPM. I have also noticed it is worse when facing uphill. Rocking the car back and forward in park will also make it knock.

Any ideas at all are welcome. I have always done all the work on this car myself but I'm thinking I'll need to take it in after thanksgiving, because I don't know where to start trying to find the problem.
 
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blacksheep-1

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Oct 21, 2006
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So if you leave the car in drive and apply a small amount of gas pedal the noise really wakes up right? If so it's probably a bottom end knock, but first, pull each plug wire one at a time, with the engine running and see if the knock goes away. This could be something as simple as carbon bouncing around the combustion chamber, or a real issue. In any case remove (or ground) one wire at a time , if the noise shuts up it's in that cylinder.
 
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kramer

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May 8, 2012
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stonewall oklahoma
well heres what happened to me , i really dont know enough about engine internals , to really help u , but there is a slim chance that its an exaust leak right before the first cat on the passenger side , ford designed their air conditioners to drip rght there ON THE EXHAUST and it usually causes them to crack , or atleast mine did there was such a huge crack in mine that only about an inch and a half of metal was what was keepng it attached to the passenger manifold , and it sounded like a engine knock , infact a certified mechanic even diagnosed it as that and said id have to have it rebuilt , thank god i dont let mechanics work on my car or i would have done it , but in this case it probably is internally , but check it check it with a flash light its very hard to see in that particular spot
 

LWilson2971

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Sep 18, 2012
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Since you're getting the noise under load I'm guessing it's a rod knock. Put your foot on the brake and rev it slowly and only to about 1800 or so RPM's if the knocking gets worse then it's for sure in the bottom end and more then likely a rod. With it continuing to get worse and you stated it does it worse going uphill ( again under load ) I'm about 95% sure you have a rod knock. I wouldn't travel to far from home if I were you and go easy on it because you don't want it coming apart at 5k RPMs
 

Tyler Neuman

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Aug 27, 2015
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So if you leave the car in drive and apply a small amount of gas pedal the noise really wakes up right? If so it's probably a bottom end knock, but first, pull each plug wire one at a time, with the engine running and see if the knock goes away. This could be something as simple as carbon bouncing around the combustion chamber, or a real issue. In any case remove (or ground) one wire at a time , if the noise shuts up it's in that cylinder.
What if when you unplug the cylinder the knocking gets louder?
 
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