L98 Engine Knock
Thread Starter
Racer
Joined: Sep 2002
Posts: 278
Likes: 14
From: Las Vegas, Nv
St. Jude Donor '14-'15
L98 Engine Knock
On the way home from work tonight the engine in my 90 convertible started to knock. When I got home I did some investigating. It is definitely a knock and not a tick. The knocking increases with engine speed. It is almost non-existant at idle. The knock is louder under the car. Last week I changed the oil and flushed the cooling system to get it ready for a new season. The car ran good all week. How do I figure out if it is a rod knock or something else without tearing the engine apart?
Pro
Joined: Sep 2001
Posts: 542
Likes: 1
From: Stuck in the 80's
Could be anything. Just for the sake of trying, check the oil filter tightness, I have heard of overtightening causing problems. I have also had one bad filter in my lifetime, it was resticting flow and caused knock at low RPM. Cheap to check, good luck!
Burning Brakes
Joined: Feb 2003
Posts: 1,218
Likes: 0
From: Rolla Mo
Originally Posted by Pats90
On the way home from work tonight the engine in my 90 convertible started to knock. When I got home I did some investigating. It is definitely a knock and not a tick. The knocking increases with engine speed. It is almost non-existant at idle. The knock is louder under the car. Last week I changed the oil and flushed the cooling system to get it ready for a new season. The car ran good all week. How do I figure out if it is a rod knock or something else without tearing the engine apart?
Doug
Thread Starter
Racer
Joined: Sep 2002
Posts: 278
Likes: 14
From: Las Vegas, Nv
St. Jude Donor '14-'15
I did burp the system after flushing the cooling system. The temp is cool - a few years ago I put in a 160 degree thermostat. The oil pressure is fine. I didn't put headers on the car - but last year I put on the Flowmaster catback system.
Race Director
Joined: Sep 2003
Posts: 16,836
Likes: 337
From: Database Error Indiana
You can take off the dust cover. You may have to loosen the starter, I cant remember. Jack up the car and have a listen under there and you can probably tell if its the flywheel. GOOD LUCK.
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Go down to your favorite auto parts house and purchase a mechanics stethoscope. Should cost about 10 bux.
Bring it home and use it to listen to different places on your engine.
Start by listening to one of the valve covers. Then the other one.
Listen to each side of the oil pan.
Listen to the accessories, particularly the air pump.
You should be able to determine what area of the engine the noise is coming from.
If it's louder from one of the valve covers then you probably have a rocker arm that has loosened a little bit.
Could be a very easy fix.
If it's coming from the oil pan area, it may cost a few dollars more to fix......... let's don't be too pessimistic at the start.
I'm hoping for you that it will be the airpump or something like that.
Good luck with it.
Bring it home and use it to listen to different places on your engine.
Start by listening to one of the valve covers. Then the other one.
Listen to each side of the oil pan.
Listen to the accessories, particularly the air pump.
You should be able to determine what area of the engine the noise is coming from.
If it's louder from one of the valve covers then you probably have a rocker arm that has loosened a little bit.
Could be a very easy fix.
If it's coming from the oil pan area, it may cost a few dollars more to fix......... let's don't be too pessimistic at the start.
I'm hoping for you that it will be the airpump or something like that.
Good luck with it.
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Thread Starter
Racer
Joined: Sep 2002
Posts: 278
Likes: 14
From: Las Vegas, Nv
St. Jude Donor '14-'15
Well here is the deal, I bought a stethoscope from the auto parts store and with the help of my son we listened to every part of the engine and accessories. I could not locate the knock coming from any part of the engine. I got under the car and listened to the exhaust pipes. The sound is coming from the passenger side exhaust pipe. Upon close examination I found the shield around the pre-cat was bent near the top and there is a dimple in the exhaust pipe like I ran over something.
The sound is definetly coming from the pre-cat. What is inside a pre-cat that would make noise? Did I knock something loose? Isn't there somekind of platinum beads inside? Can I eliminate the pre-cats and still pass the air pollution test?
The sound is definetly coming from the pre-cat. What is inside a pre-cat that would make noise? Did I knock something loose? Isn't there somekind of platinum beads inside? Can I eliminate the pre-cats and still pass the air pollution test?
Drifting
Joined: Mar 2005
Posts: 1,923
Likes: 0
From: GA
Originally Posted by Pats90
What is inside a pre-cat that would make noise? Did I knock something loose? Isn't there somekind of platinum beads inside? Can I eliminate the pre-cats and still pass the air pollution test?
You should be able to pass emissions without the pre-cats (except maybe in the more strict zones) especially if you install new high flow/efficency cats.
