C4 1992 fuel consumption and misfire problems

[JackCELER]

The car is an 1992 Corvette with automatic gearbox.

Troubles beginning 2 years before, I was thinking of optispark failure. The car have misfire, detonation on the exhaust pipe (no cat) and it smell fuel... The car didn't run good but can take road for small distances. But the optispark was replace for less than 2 years and 5000 kilometers

I have tested all the ignition system but not the optispark, and the car was going well after cleaning ground and connectors. Good fuel consumption, no misfire, no detonation on the exhaust... 4 weeks with no problems.

But last week, problem became... 75 liter of unlead fuel for 250 kilimeters.... on cruising mode... Detonation on exhaust, dark smoke and loss of power.

I was thinking on fuel injection problems. How to test fuel pressure? Can I use the valve on the injection line?
What could be wrong also?

[NEVRL8T]

What brand of Optispark was it replaced with. Cheap Ebay one?

[JackCELER]

I dont know. It was replace by a french workshop. I think it is not an AC-DELCO optispark.

[ToolGuy]

Yes if there is a shrader valve on the fuel rail, then you can check fuel pressure from it with a gauge.

Do you have a check engine light on?

When were you plugs and wires replaced last? I assume they are good since the Optispark was replaced by itself according to what you said above.

[JackCELER]

Ok, I will try to use a gauge on the shrader valve.

spark plugs and wire are good. But not for a long time for the spark plugs because of the amount of fuel....

I was searching if oxygen sensor can make this kind of trouble?

Most of the time, the car doesn't run well for many weeks, but no engine light coming. Last day, engine light come, with DTC code for right oxygen sensor..... It's look like normal because of the fuel consumption and misfire.... Is a faulty oxygen sensor make that or is it a collateral damage?

I try to test it. infinite resistance... I don't succeed to unscrew it. The plug was clean. And now car work well....
But, I surprised. No engine light come when I try to run the car with oxygen sensor unplugged...

I don't find the problem, I'm all around....

[jimbow]

The ICM, Coil and the wire harness from the opti to the ECM connector on the passenger side intake can all be issues.

You'll need a factory service manual for the troubleshooting procedure.
If the o2 sensor is bad it will throw a code, if its lazy it won't
Several folks are reporting issues with Bosch o2 sensors, so try a different brand.

[ToolGuy]

Originally Posted by JackCELER

Ok, I will try to use a gauge on the shrader valve.

spark plugs and wire are good. But not for a long time for the spark plugs because of the amount of fuel....

I was searching if oxygen sensor can make this kind of trouble?

Most of the time, the car doesn't run well for many weeks, but no engine light coming. Last day, engine light come, with DTC code for right oxygen sensor..... It's look like normal because of the fuel consumption and misfire.... Is a faulty oxygen sensor make that or is it a collateral damage?

I try to test it. infinite resistance... I don't succeed to unscrew it. The plug was clean. And now car work well....
But, I surprised. No engine light come when I try to run the car with oxygen sensor unplugged...

I don't find the problem, I'm all around....

I personally dont have enough experience with O2 sensors to know if a poor running engine will kill an O2 sensor. I guess it could though if the engine were dumping to much fuel in the exhaust system, but that's just a guess. I know a bad up stream O2 will take out a catalytic converter if left like that too long... But of course that's not your case.

I too am surprised when you dicsonnected the O2, you did not get a check engine light. Weird.

You are right though a bad O2 will result in poor fuel consumption.

Now I'm stumped here! Should you go after the O2 first now or what? Then see how the car runs?

[JackCELER]

thank you for your answer.

I'll try to replace o2 sensors, and see what happening... Is the car doesn't run better, I will unscrew new 02 sensor for not killing them with too much fuel....