LT1 Engine rattle, bad cat?
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Instructor
Joined: Jul 2006
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From: Erie PA
LT1 Engine rattle, bad cat?
I got a 1993 LT1 w/manual. About 2 weeks ago I started to hear noise coming from the lower engine area. The sound is like a rattle that pulsates with the engine idle. It seems to go away when I increase the RPM’s (or maybe it’s still there but can not be heard over the sound of the engine when I rev. it up) If the engine is cold the noise is not present. Only after the car is warmed up for about 10-15 minutes do I hear it. I used a stethoscope to locate the area of the noise. I have found that the drivers side catalytic converter has the noise much, much louder then the passenger side cat. I’m hoping that the problem is not internal (like rod bearings, or lifters). I have driven the car about 100 mile since the noise began and it is getting a bit louder. Would a cat that is going bad make that kind of noise but only when hot?
Instructor
Joined: Feb 2001
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From: Acworth Ga
Could be. My 2001 Park Ave rattled when cold. Single cat and when i replaced it the rattle went away. Psst the gas mileage went back up too. If you can pull it off the exhaust pipe and see inside try to move the honeycomb around. If it does it is shot and replacement is inevitable. Hope this helps. Have fun.
Instructor
Joined: Jan 2004
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From: I celebrate their entire catalog
I had something similiar going on in my 95 LT-1 auto a couple of years ago. A rattling noise on the passenger side, down low. I had it traced to the converter or starter or exhaust manifold shield.
One day I cleaned my MAF with a can of MAF cleaner (it was filthy) and the noise went away and has never returned. I don't know how or why or what, but there it is.
I forget if a 93 uses a MAF or a speed density sensor, but cleaning things is hardly ever a bad idea!
One day I cleaned my MAF with a can of MAF cleaner (it was filthy) and the noise went away and has never returned. I don't know how or why or what, but there it is.
I forget if a 93 uses a MAF or a speed density sensor, but cleaning things is hardly ever a bad idea!
Le Mans Master
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St. Jude Donor '12
It could also be a dual mass flywheel beginning to destroy itself.
Thread Starter
Instructor
Joined: Jul 2006
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From: Erie PA
Update: Bad Cat
I decided to pull the left cat off the car today. Sure enough there was a loose piece of ceramic bouncing around inside. I though it be best to gut the whole thing. Unfortunately all 6 studs broke off when I was removing it from the car, turning it into a 5 hour job. I live in Pennsylvania so there is only a visual inspection for the converters. One question, should I also gut the right converter or would it be ok to run with one gutted and one working? Thanks for the help.
Tech Contributor
Joined: Oct 2008
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From: Custer, WI
I decided to pull the left cat off the car today. Sure enough there was a loose piece of ceramic bouncing around inside. I though it be best to gut the whole thing. Unfortunately all 6 studs broke off when I was removing it from the car, turning it into a 5 hour job. I live in Pennsylvania so there is only a visual inspection for the converters. One question, should I also gut the right converter or would it be ok to run with one gutted and one working? Thanks for the help.
Why not go ahead and gut both? If you are going illegal, you might as well go the whole 9 yards.
I don't know if it would cause pressure imbalances between the two banks or not.
Racer
Joined: Nov 2001
Posts: 392
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From: Churchville PA
I decided to pull the left cat off the car today. Sure enough there was a loose piece of ceramic bouncing around inside. I though it be best to gut the whole thing. Unfortunately all 6 studs broke off when I was removing it from the car, turning it into a 5 hour job. I live in Pennsylvania so there is only a visual inspection for the converters. One question, should I also gut the right converter or would it be ok to run with one gutted and one working? Thanks for the help.
Also, where did you get the studs that broke? Nobody local has these and the dealer will only sell packs of 10.
Thread Starter
Instructor
Joined: Jul 2006
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From: Erie PA
Wow-same EXACT issue in my 96 lt1!! Tried pulling my driver side Cat and busted 1of the 3 studs on the exhaust manifold and couldn't get the bracket off the back of the driver side cat. I got the 2 nuts and the one bolt off but, couldn't get the 2 studs out the back of the cat that go through that bracket. How did you get these off?
Also, where did you get the studs that broke? Nobody local has these and the dealer will only sell packs of 10.
Also, where did you get the studs that broke? Nobody local has these and the dealer will only sell packs of 10.
For the drivers side studs that broke off I used my Craftsman damaged bolt remover http://www.sears.com/shc/s/p_10153_1...8&blockType=G8
I heated the exhaust manifold red hot with an acetylene torch around each stud and was able to back out the stud with the stud remover. By the time I removed the 3 studs on the drivers side the stud remover was worn enough that it would not grip any more. I ended up cutting the studs on the back side of the cat flush and then drilled the old stud with a 5/16” drill and tapping the hole with a 3/8-16 tap. I also had to drill and tap the pass. side manifold. I got my 3/8” studs at Advance Auto, they came in a 6 pack for around $7.00. If you think getting the cat off the drivers side is fun wait till you have to do the passengers side. All together it took me about 12 hours to do both sides. If I had to do it over again I would just gut the cats on the car by cutting a opening in the bottom of the cat, remove the ceramic, and weld the piece back on with a mig welder. Good luck.
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Heel & Toe
Joined: Aug 2021
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I sure appreciate these threads. I had a rattle in the passenger side cat and I just cleaned the MAF sensor and it went away! I still think it may be a bad cat, so getting those gutted is gonna be something I do. Is back pressure an issue on these cars? I have a 96 lt4. I ask because I removed the cats on my 2000 ram 2500 and went straight pipe. I lost about 30 miles per tank and some acceleration power when I did that, and had to reduce down my tailpiece to restore the back pressure. I also was reading about people breaking bolts getting the cats off. I'll tell you all that a great way to keep from breaking bolts, especially those kind, is to spray down the bolts with wd-40. But don't just do it right before you start. If possible, do it multiple times over a couple days. The oil will penetrate if you give it time and extra applications. I broke lots of bolts before a friend told me this trick. Now I do it, and can't think of the last time I broke a bolt.
Thread Starter
Instructor
Joined: Jul 2006
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From: Erie PA
Wow! I forgot about that experience 10 years ago busting the rusty exhaust studs in the hard-to-reach engine compartment. I don't want to do that again.
That car (1993) is long gone. Replaced in 2013 by a 2002 black convertible and then replacing that one last year with a 2011 Grand Sport convertible.
I do remember on the 1993 that when I gutted both the driver's side and passengers side cats that the performance increased substantially without any lose to mpg's
The exhaust tone also had a nice increase in the sound levels with a raspier sound when revving and a little bit of a burble on downshifting. (It sounded really good)
That car (1993) is long gone. Replaced in 2013 by a 2002 black convertible and then replacing that one last year with a 2011 Grand Sport convertible.
I do remember on the 1993 that when I gutted both the driver's side and passengers side cats that the performance increased substantially without any lose to mpg's
The exhaust tone also had a nice increase in the sound levels with a raspier sound when revving and a little bit of a burble on downshifting. (It sounded really good)
Safety Car
Joined: Apr 2016
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From: N.E. Ohio OH
Finalist 2020 C4 of the Year - Modified
Heel & Toe
Joined: Aug 2021
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Thanks Pacat and Drcook, for your replies. If I do trigger the ses light, does it throw codes I can check with my obd 2 scanner? The cel has been on since I bought the car, so I keep the scanner in there and check it every time I drive to make sure nothing new is happening. Thanks.
Drifting
Joined: Feb 2016
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From: Simi Valley CA
If your car has sensors after the cats, its not enough to just trick the o2s. They are part of the car's tuning. IF you do not tune and monitor your afr you risk running too lean and that cracks pistons.
Heel & Toe
Joined: Aug 2021
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Thanks topfuel67. I didn't see 02 sensors after the cats, just before. I will get under there and take another look. Is there somewhere I could type in my VIN and be able to check for what was stock on this car originally? Turns out that just about everything the seller told me about this car is lies, and now I'm not sure what half *** shortcuts he did getting it ready to sell. The cel has been on since I bought it. Seller claimed it was because he hollowed out the cats. My code reader always gives me the P0100 code and I haven't figured out what is causing it yet. It intermittently throws P0411, telling me incorrect purge flow. I found some bad vacuum lines and replaced them. That cleared that one for a while, but today it returned. The original EGR valve has been removed and it has a smaller one bolted to the back of the intake. Anyone have any ideas I could try?
Safety Car
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From: N.E. Ohio OH
Finalist 2020 C4 of the Year - Modified
Here is a discussion of the O2 sensors. The front 2 are for engine tuning the back 2 are to make sure the cats are there and functioning.
https://www.corvetteforum.com/forums...-1996-lt4.html
lkwd777 where are you located ?
https://www.corvetteforum.com/forums...-1996-lt4.html
lkwd777 where are you located ?
Safety Car
Joined: Apr 2016
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From: N.E. Ohio OH
Finalist 2020 C4 of the Year - Modified
Way too far to hook my scanner up to your car. Maybe another person here has a good scanner that allows you to see the PID's etc and watch real time. I do that with my '96.
Heel & Toe
Joined: Aug 2021
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I unhooked the battery and the purge code cleared again. Had new tires put on today and the car rides like butter. Thanks Drcook. I guess that at some point I will have to take it to someone for a full diagnostic. Wish it could be you.
Drifting
Joined: Feb 2016
Posts: 1,384
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From: Simi Valley CA
My 92 only has the pre-cat o2s. I'm not sure when they got to adding the ones after the cats. It may have been in 96 when it went to ODBII. The rear o2 sensors monitor the efficiency of the cat and do change the tuning based on the performance of the cat. If you gut the cat and do not tune for it, the car's computer will make it run very lean and will destroy your pistons.