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I'm new here and thought I would reach out for some advice. I have a 1994 manual LT1 with about 70,000 miles on it. It has developed a vibration in the motor while parked in neutral. Do you think it's likely to be the harmonic balancer? Other things I should look for? What's the easiest way to diagnose this? Have you replaced the harmonic balancer? Any tricks? That frame rail is right there in the way if I'm not mistaken.
Try making a chalk line across the front...from the inner ring to the edge of the outer ring. Then run the engine for several minutes and turn it off. If the line you drew isn't still straight, then the balancer is bad.
If you have to replace...you'll need a standard puller tool to remove and an install tool too. While mine isn't an LT1, I know that there isn't much space and you may have to carefully bend a power steering line just a bit to get the tool situated. On the install tool, smaller is better...I used the 61740 from Moroso (bought at Summit Racing it's MOR-61740). Beware of other install tools that are for small block AND big blocks...these will likely be too long to use on this car.
Another tool that will help on this (and many other projects) to loosen bolts is a right-angle impact wrench. I use the Milwaukee 2564...so handy.
Wow thanks informan! I'm going to try this. Also thanks for the tip about the right angle impact, it's one Milwaukee tool i don't have yet hahaha. I'll let you know what's up!
Ok I had a little time to work on it. I'm pretty sure the harmonic balancer is good. I marked it and it didn't slip. So a little back story, I first noticed the problem last fall when I put it away. That was the last time I drove it for the year. So I kind of let this simmer for the winter. I decided to take it for a drive today and I'm 95% the engine is missing and that's what's causing the problem. I bought the car a year ago. It had receipts for a new optispark, plugs and wires in 2023. I pulled the codes and didn't get anything, just c12. I ran the car for a minute and checked the temperatures on the exhaust manifold and its possible cylinder #3 was 50 degrees colder. It's kinda tough to tell because it shares the manifold pipe with cylinder 5. It seemed like the cylinder 5 side was hotter. The last clue I have is that the exhaust smells like its running rich. I suppose next I should pull the plug on cylinder 3 and see if I'm getting a spark? How do you think I should proceed? Thank you for any help!
Currently chasing the same symptoms with my 94 in another thread. After a vacuum check, an injector, shows a possible o-ring leak. Digging into it this weekend. Good luck!
I haven't checked the motor mounts. It didn't look like the engine was moving very much. It was really down on power when i drove it so I feel like it has to be misfiring. I'm going to check the motor mounts too while I'm.in this. I'm going to check these plugs too. I have quite a busy weekend, but i might get a little time so we'll see. I'll get back to you all for sure with what I have. Thank you so much for all of your help.
OK, so I had a little time to work tonight! I checked for spark and sure enough I was missing spark on cylinder 3. I found it by hooking my timing light to the plug wire. I followed the plug wire back to the optispark and felt to make sure it was plugged in. It felt good but I pushed on it as much as I could. Then I fired it up again and I had spark. However, when I revved the motor the light would sometimes cut out. I feel like the timing light should just fire faster, don't you think? Or is it not really accurate say above 2k rpm? The motor was running much better but still doesn't feel 100%. Would you replace the plugs and wires to be sure? They're 3 years old. Then if I were, what plugs and wires would you use? I seem to remember reading something about LT1s liking certain plugs. What do you think?
So I pulled a couple plugs: the one on the top is the one that was misfiring the worst. It was not very tight, does that matter? I ordered new plugs and wires so I'll start there. These plugs are the ac Delco double platinum plugs, does that matter? Like I said I ended up getting spark on that #3 cylinder, but it's still not running great. I wonder if there are multiple misfires or a weak coil or something? Any help is greatly appreciated!
Plain copper plugs work really well. No need for fancy here. If you have an obvious ignition issue with one cylinder truly seems plugs/wires are called for.
94 and 95 have very versatile PCMs. Have a windows laptop? Even an ancient one? If so, you are just a >$100 diagnostic cable and some free software (eeHack) away from having a very powerful diagnostic tool.
Looks like the bottom plug is original. The top plug looks to be a new plug, which is odd it's worse looking but that could be because someone forgot to torque down the plug. At this point all new plugs is a good idea. You can do the plugs and run it again to check status. Plug wires are quite a bit more involved but not overly difficult on the LT1.
Hey y'all thanks for the advice! Djpink, I'll put the new plugs in first and check it. I have the ngk Tr55's or whatever. Jmgtp I used to have something like that wire for my old car, that was nice. I'm fairly computer savvy, so that would be a good thing to get. What cable should I get? Is it possible to use that on other cars also? Again thank you all so much for the help. What a bunch of nice people here.
Hey y'all, just wanted to give an update on my Vette. I did the plugs and wires with MGK tr55 and Taylor wires and now it runs great. Thank you so much for all the help. There's a bunch of cool people here!
Motor Vibration 1994 LT1
