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C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Bad Optispark?

 
Old 05-14-2019, 07:03 AM
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Chuck80
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Default Bad Optispark?

115K Miles, just had a leaky intake gasket, and valve cover gaskets replaced. I really hope the technician didn't get coolant on the Opti. Engine used to be smooth while accelerating, but after the gasket replacement, it's different above 2K RPMs. I'd describe the sound as a machine gun, or someone rolling their Rs like "Guitar-r-r-r-r-r-r-ra."
I swapped the original plug wires (what a PITA on the diver's side!) and the engine was great for about 5 minutes. Now the noise is back.

Is my Opti toast?
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Old 05-14-2019, 07:15 AM
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Forgot to mention - It's a 1992, with the non-vented Opti. Yay.
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Old 05-14-2019, 08:13 AM
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MatthewMiller
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Can't rule out the opti, but if the noise changed when you swapped plug wires, then that leads me to think that isn't the problem. When your car stutters, what does your tach do? Unless it goes berserk, it's probably not the opti. I honestly think the whole coolant-in-opti thing is overblown. It's pretty hard for moisture to get inside the opti if the sensor connection is still plugged in. I think the culprit for most opti failures is corrosion due to condensation and ozone buildup.

ETA: it sounds like you're describing a single (or maybe two) cylinders that are missing regularly. That is also not a likely failure mode for the opti. I'd be looking at plug wires and plugs. It is possible that there is a bad terminal on the opti's cap, though.

Last edited by MatthewMiller; 05-14-2019 at 08:15 AM.
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Old 05-14-2019, 09:56 AM
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Kevova
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Only coolant involved is to throttle body. Wires can stay in.place. As you play with your car the technician loses liability. Who's to say it's not your fault. Take it back tell him what's wrong and let him review repair. A scope test should shop ignition issues.
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Old 05-14-2019, 09:02 PM
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Chuck80
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The noise was there before I swapped plug wires. It started after the shop replaced gaskets. I was told the wires were original, so I was hoping replacing the wires might be an easy fix.
The tach doesn't seem to go berserk. I'm trying to rule out any easy problems before I dive into the waterpump and opti. The plugs are possibly original as well. Maybe one or more be fouled?

Originally Posted by MatthewMiller View Post
Can't rule out the opti, but if the noise changed when you swapped plug wires, then that leads me to think that isn't the problem. When your car stutters, what does your tach do? Unless it goes berserk, it's probably not the opti. I honestly think the whole coolant-in-opti thing is overblown. It's pretty hard for moisture to get inside the opti if the sensor connection is still plugged in. I think the culprit for most opti failures is corrosion due to condensation and ozone buildup.

ETA: it sounds like you're describing a single (or maybe two) cylinders that are missing regularly. That is also not a likely failure mode for the opti. I'd be looking at plug wires and plugs. It is possible that there is a bad terminal on the opti's cap, though.
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Old 05-14-2019, 09:05 PM
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I talked to them about the problems it developed after their work, and they said it could be the opti. Got an estimate for opti replacement with waterpump, wires, other minor stuff, labor for $2K. Before I dive into opti replacement, I want to exhaust any easy fixes.

Originally Posted by Kevova View Post
Only coolant involved is to throttle body. Wires can stay in.place. As you play with your car the technician loses liability. Who's to say it's not your fault. Take it back tell him what's wrong and let him review repair. A scope test should shop ignition issues.
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Old 05-14-2019, 09:25 PM
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It's not the opti. That's the scapegoat for every LT1 problem, but it rarely actually is the problem. This is something else.
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Old 05-15-2019, 08:57 PM
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Originally Posted by MatthewMiller View Post
It's not the opti. That's the scapegoat for every LT1 problem, but it rarely actually is the problem. This is something else.
I like the what you're saying!

I drove it today, and it doesn't run rough until the engine is warmed up. I had 5-7 minutes of smooth accelerating. The tach is always smooth.
I guess I'll pull the spark plugs and check them out.
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Old 05-15-2019, 10:00 PM
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Originally Posted by Chuck80 View Post
I like the what you're saying!

I drove it today, and it doesn't run rough until the engine is warmed up. I had 5-7 minutes of smooth accelerating. The tach is always smooth.
I guess I'll pull the spark plugs and check them out.
This sounds very much like some sensor is bad. The car is fine while it's warming up in open-loop mode. Then when it hits its target temp and goes into closed-loop mode, it begin paying attention to all the sensors. One of them is dead or dying. On my car this happened with a bad O2 sensor. I hear that the Coolant Temp Sensor is a common culprit too. Anyway, that's what I'd be looking for.
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