Engine Noise Diagnosis
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Joined: Apr 2004
Posts: 52
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From: Terrell TX
[Resolved] Engine Noise Diagnosis
Recently my daily driver 1996 CE with 155K miles on it started making a rather loud and annoying noise that seems to be coming from the vicinity of cylinders 5 and 7 on the drivers side of the engine. It seems to have progressively gotten worse and I've stopped driving the car for the time being. 
The noise seems to get quieter as the engine warms up, and seems to have a frequency of 1/2 engine speed. Here is a link to an audio clip I made; the mic was placed beside the exhaust manifold and the engine started cold, idle was about 1000rpm and the last section of the audio was with the engine revved to 1500rpm.
I haven't done much troubleshooting with the engine yet, and cutting fuel to the cylinders in question does not seem to change anything.
What should I do next? I was going to go get a mechanics stethoscope to try to pinpoint the sound a bit better, Autozone was a no-go so I'll try O'reilly tomorrow. I have the FSM (surprisingly brief on engine noise unless there is another section buried somewhere) to help me along and I'd rather get my hands dirty than pay big bucks for someone to do it for me.
Any thoughts would be greatly appreciated,
Thanks!
The noise seems to get quieter as the engine warms up, and seems to have a frequency of 1/2 engine speed. Here is a link to an audio clip I made; the mic was placed beside the exhaust manifold and the engine started cold, idle was about 1000rpm and the last section of the audio was with the engine revved to 1500rpm.
I haven't done much troubleshooting with the engine yet, and cutting fuel to the cylinders in question does not seem to change anything.
What should I do next? I was going to go get a mechanics stethoscope to try to pinpoint the sound a bit better, Autozone was a no-go so I'll try O'reilly tomorrow. I have the FSM (surprisingly brief on engine noise unless there is another section buried somewhere) to help me along and I'd rather get my hands dirty than pay big bucks for someone to do it for me.
Any thoughts would be greatly appreciated,
Thanks!
Last edited by ShaneL; Apr 16, 2010 at 07:26 PM.
Racer
Joined: Sep 2008
Posts: 456
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From: FL
I am pretty sure you have a problem I fixed 2 days ago.
It is cracked exhaust manifold.
When I used my stethoscope with stick I couldn't hear that sound. I could hear it w/o stick, not touching engine. Sound is not clear because it is under shield.
My manifold had 2 cracks.
It is cracked exhaust manifold.
When I used my stethoscope with stick I couldn't hear that sound. I could hear it w/o stick, not touching engine. Sound is not clear because it is under shield.
My manifold had 2 cracks.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Either way I would sure want to know which one and not drive it until I knew for sure. Sort of pick what you want to take apart first I would go from whatever you think is easiest first..LOL.. I hate working on exhaust so I picked valve cover.
Thread Starter
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Joined: Apr 2004
Posts: 52
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From: Terrell TX
Got a stethoscope today, and can hear the noise when I put it on various places under the valve cover. It gets quiet fairly quickly when the engine warms up so I'm having a hard time pinpointing it, but it seems to be nearest the exhaust valve rocker stud on cylinder #7; those studs seem to be fairly noisy places either way though so I'm not too sure of it.
On the exhaust idea, I got rid of the cast iron bricks a few years ago in favor of long tubes, but welds do tend to crack occasionally so I can't dismiss that idea.
If I knew for sure it would fix my problem, I'd be tempted to do a cam swap and replace lifters, pushrods, rockers, and springs, and have the heads checked at a shop.
Thanks for the input!
On the exhaust idea, I got rid of the cast iron bricks a few years ago in favor of long tubes, but welds do tend to crack occasionally so I can't dismiss that idea.
If I knew for sure it would fix my problem, I'd be tempted to do a cam swap and replace lifters, pushrods, rockers, and springs, and have the heads checked at a shop.
Thanks for the input!
Race Director
Joined: Apr 2003
Posts: 17,699
Likes: 1,667
From: moraga ca
On the exhaust idea, I got rid of the cast iron bricks a few years ago in favor of long tubes, but welds do tend to crack occasionally so I can't dismiss that idea.
If I knew for sure it would fix my problem, I'd be tempted to do a cam swap and replace lifters, pushrods, rockers, and springs, and have the heads checked at a shop.
Thanks for the input!
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