1991LS400 Posted May 1, 2005 Share Posted May 1, 2005 Hey guys, Everytime I get in my car, stick the key in the ignition, and turn the car on there's this sort of "THUMP" or knock that I can hear inside the dashboard. It could be from the engine but I'm just saying where I can hear it from inside the cabin. This knock is driving me crazy and I don't know if it's something that needs immediate attention. Second question, how would I know when my catalytic converters need to be changed? They are 13 years old...is that one way to tell? No, seriously, do they need to be changed if they're that old? Lastly, does anyone know how to install a strut bar on a 1991 LS 400? Is there a diagram somewhere on the internet that can explain how? Is this a DIY job or do I need to take it in to a shop? Quote Link to comment Share on other sites More sharing options...
1991LS400 Posted May 1, 2005 Author Share Posted May 1, 2005 ^ up Quote Link to comment Share on other sites More sharing options...
cruznroadking Posted May 1, 2005 Share Posted May 1, 2005 The answer to your question on cat replacement. My brother has a 91LS400 with 245k & has the original cats. Only replace them if they don't pass smog test. Quote Link to comment Share on other sites More sharing options...
JPI Posted May 2, 2005 Share Posted May 2, 2005 The answer to your question on cat replacement. My brother has a 91LS400 with 245k & has the original cats. Only replace them if they don't pass smog test. ← This knock only occur when you first started up the car? JPI Quote Link to comment Share on other sites More sharing options...
1991LS400 Posted May 2, 2005 Author Share Posted May 2, 2005 This knock only occur when you first started up the car?JPI ← yes. Quote Link to comment Share on other sites More sharing options...
VMF Posted May 2, 2005 Share Posted May 2, 2005 replace cats only when ur check engine light is gonna come up and the code is gonna show the th o2 sensor problem Quote Link to comment Share on other sites More sharing options...
1991LS400 Posted May 2, 2005 Author Share Posted May 2, 2005 Ok guys, well what about the "knock?" Quote Link to comment Share on other sites More sharing options...
nc211 Posted May 2, 2005 Share Posted May 2, 2005 Your "knock" is a bad engine mount. My 95 did the exact same thing. Right when you start it, especially after it's been sitting awhile, a thump like knock is heard. I had the engine mounts replaced and it was fixed. Plus, they also smoooothed out the car big time! Made the engine much much more quiter in the cabin. Quote Link to comment Share on other sites More sharing options...
1991LS400 Posted May 2, 2005 Author Share Posted May 2, 2005 Your "knock" is a bad engine mount. My 95 did the exact same thing. Right when you start it, especially after it's been sitting awhile, a thump like knock is heard. I had the engine mounts replaced and it was fixed. Plus, they also smoooothed out the car big time! Made the engine much much more quiter in the cabin. ← Thanks for the feedback but I believe you're wrong nc211. I had both (2) motor mounts changed on my 1991 LS 400, and yes, when I changed both motor mounts the vibration noise that could be heard in the cabin when idle stopped as well, and the ride became much quiter and smoother. When idle, my car now sounds as if it's not even on. However, unless the 1st Gen LS 400's came with 3 mounts, I doubt that's the case for the "knock" or "thump" like sound I keep hearing when I turn on my car. Any other ideas? Please help. P.S. When I said "3 mounts" I wasn't including the transmission mount. I have a new tranny mount. I am referring to a 3rd motor mount, if there is one. Quote Link to comment Share on other sites More sharing options...
1991LS400 Posted May 2, 2005 Author Share Posted May 2, 2005 ^ up Quote Link to comment Share on other sites More sharing options...
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