Rapping Noise 1500 to 2500 Rpm

[wantattype2]

Hi, my car has a rapping noise between 1500 to 2500 RPM sounds like its in the front of the motor around the cam sensor belt tensioner area. When I drive the car under light throttle it shows knock on the scanmaster at each gear change. The car runs fine with no noise at idle or above 2500 RPM. I put a stethoscope on the cam sensor housing and it seemed to be the loudest there so I put in my spare cam sensor, belt tensioner and tightend all the bolts on the A/C compressor brackets but the noise is still there. Any ideas ?

 

[Nick Micale]

Set the engine RPM to where you hear the knock and then remove one plug wire at a time. If the noise stops, probably a rod bearing.

 

[wantattype2]

Thanks Nick, I'll try that today. I should have said that it is more of a tapping noise like the old SBC fuel pumps use to make.

 

[wantattype2]

Nick, just wanted to let you know that when I got to #5 plug wire the noise went away. Thanks for you help.

 

[threerail]

not trying to step on nicks reply here but... my experience has been he described how to check for a bad wristpin... a rod knock would still be there doing what he said, it would quiet some with wire removed but not completely. a bad wristpin goes quiet with no bang on top of it to hammer the play in it. a rod knocks loud usually with or with out firing the cylinder when it reaches full up and down extension unless its early in its development. just visualize this in your head , macks sense right, at least in my head it does. good luck, rob

 

[Nick Micale]

not trying to step on nicks reply here but... my experience has been he described how to check for a bad wristpin... a rod knock would still be there doing what he said....................

I can only comment on what my experience has been over the years, and certainly and internal noise is only a guess until the actual cause is found.

I the many times I have tried this method, it has always been a rod bearing which is a very common occurrence on these engines. After dealing with many hundreds of rebuilds, we have found VERY few wrist pin problems, so in my opinion the first choice would be a bad rod bearing. :smile:

 

[turboxan]

It is easy enough to pull the oil pan off with the motor still in the car and check your rod bearing, also check the trust bearing, to see if your crank is not moving back and forth. I think the max end play is .080