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Discussion Starter · #1 ·
Hey guys, have a ‘96 TA with a rebuilt LT1. Bought the car in April and have been slowly replacing and updating on the car. Did the plugs last week, PITA by the way, and no issues. Today I’m driving on the highway and hear it running rough out of no where. Quarter mile later I get the service engine soon. I put the reader on it and I’m getting multiple misfires on 5&6 only. Any ideas? New plugs and driven about 100 miles on them. I’m new to the LT1 so any help would be appreciated
 

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My first bet would be to double check the plug wires. When I first bought my 97 Formula, I had number 6 vibrate off after about 2 weeks. Misfire out of nowhere. Slipped it back on, and I havent had that problem come back on.

As a heads up, resist the urge to blame the Optispark for everything. While it can be the cause of some problems, taking the time out to properly diagnose it will save you time, frustration, and money. To do that, you will need an Oscilloscope. PC based ones can be had for around $70, and will let you see if the Opti is sending the proper square wave signals.

shbox.com has a ton of useful information, including some diagnostics for the Opti, as well as a ton of other common issues with the LT1.

P.S. Welcome to the forum, and I hope you are enjoying your new TA!
 

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Discussion Starter · #3 ·
Thank you much, it was just odd to me that 5 and 6 hit, I’ll check the plugs out tomorrow. Ty!
 

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Try misting the plug wires with some water from a spray bottle. Run engine at night and look for spark leakage.

You changed the plugs, what about plug wires, opti cap & rotor. These are things that wear out and need to be changed from time to time. And word of advice, buy only GM, Delco, or Delphi cap & rotor.

How about your coil. I recently had a miss on my 90 camaro daily driver. I changed plugs, wires, cap & rotor. Still missed. Took a good look at coil, found that high tension lead where coil wire was plugged in was very corroded.

Used sanpaper to clean terminal and car ran better. But still would miss from time to time. Installed new coil and problem solved.

As recommended above, buy a PC based oscilloscope. If you plan on keeping your lt1 equipped car, this is a vital test instrument. Use it to check low & high resolution pulses from opti. They should be nicely formed square waves. Scope also good for checking that pesky 50 hertz fuel enable signal sent by BCM to PCM. It's a square wave also.
 

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Discussion Starter · #5 ·
Thank you for the advice, I’m in the process of changing the wires, had them ordered and they’ll be in tomorrow. I’m going to open the cap tonight and check it out. Hopefully it’s just a little dirty and with the new wires and clean cap it will be running right again.
 

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Discussion Starter · #7 ·
Just got done changing out all the wires, 5’s was destroyed. 6’a didn’t show any bad signs but all back and re-run. Took it for a ride after clearing the codes and it’s running mint. Was definitely a wire issue after replacing the plugs. Thanks for all the advice and help.
 
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