110 race fuel

[Brian P]

Hey everyone. Last summer I decided to run 110 leaded race fuel in my 97 camaro LT1. I have hot cam, heads, intake, etc. Stock injectors, long tube headers- no cats. I ran the car with the fuel in it, ran very strong for about 2 days- then began to run crappy. I believe I destroyed my O2 because my A/F gauge was reading extremely lean. I replaced the O2 and drained the tank. Started and took a few minutes but it seemed to run better. My concern now is that the gauge is still saying that engine is running lean? and when it gets up to operating temp, it seems to be running fat. I could see and smell unburned fuel coming from exhaust. I didn't replace the plugs yet but I'm wondering if that may be my case, did I destroy the plugs when using the 110 leaded fuel??? I did remove the #1 plug for inspection, was pretty black? Would fouled or bad plugs cause my A/F gauge to say engine runs lean?? The car ran great before I put this fuel in it, the gauge was normaly reading "stoich". Please help- this sucks.

[Injuneer]

Most likely sequence of events:

Leaded fuel damaged the O2 sensors, and caused them to indicate "lean" when the engine wasn't running lean.

In response the PCM poured in extra fuel, and it was actually running pig rich.

The plugs foul because of the rich condition, and the engine starts to misfire.

You replace the O2 sensors but its too late, the plugs are already fouled.

The misfiring continues, and the new O2 sensors see the air that isn't being consumed by the fuel when the cylinder misfires - a "false lean" condition.

PCM responds to false lean by pouring in more fuel, continures to run pig rich.

Additionally, you keep referring to your "O2" (singular). You are aware that your 97 has a pre-cat O2 sensor in each bank of the exhaust system, and you did replace them BOTH, correct?

Does your exhaust system include cats? Typically, the lead in the fuel destroys the cats a lot faster than it destroys the O2 sensors.

Plugs continue to foul and it just keeps getting worse.

Helpful hint for the future.... do NOT waste your money on leaded racing fuel. It does not help an engine that does not need 110 octane fuel. I can run my engine (almost 11:1 compression, 500hP NA) on 94-octane unleaded and make maximum power. Dyno proven that upping the octane did not allow us to make any extra HP, no matter what we did to the tune. With a 125-shot of nitrous (625HP at the flywheel) it reached maximum power on 100 octane unleaded. The only time I use leaded racing fuel is when I spray the 300-shot (800HP/800ft-lb at the flywheel).

[Brian P]

Most likely sequence of events:

Leaded fuel damaged the O2 sensors, and caused them to indicate "lean" when the engine wasn't running lean.

In response the PCM poured in extra fuel, and it was actually running pig rich.

The plugs foul because of the rich condition, and the engine starts to misfire.

You replace the O2 sensors but its too late, the plugs are already fouled.

The misfiring continues, and the new O2 sensors see the air that isn't being consumed by the fuel when the cylinder misfires - a "false lean" condition.

PCM responds to false lean by pouring in more fuel, continures to run pig rich.

Additionally, you keep referring to your "O2" (singular). You are aware that your 97 has a pre-cat O2 sensor in each bank of the exhaust system, and you did replace them BOTH, correct?

Does your exhaust system include cats? Typically, the lead in the fuel destroys the cats a lot faster than it destroys the O2 sensors.

Plugs continue to foul and it just keeps getting worse.

Helpful hint for the future.... do NOT waste your money on leaded racing fuel. It does not help an engine that does not need 110 octane fuel. I can run my engine (almost 11:1 compression, 500hP NA) on 94-octane unleaded and make maximum power. Dyno proven that upping the octane did not allow us to make any extra HP, no matter what we did to the tune. With a 125-shot of nitrous (625HP at the flywheel) it reached maximum power on 100 octane unleaded. The only time I use leaded racing fuel is when I spray the 300-shot (800HP/800ft-lb at the flywheel).

Hey thanks for the quick reply-

When I said "02", I was referring to 1. I have long tube headers and only 1 O2 on right bank. I have sims on or where post cat would be. There are no cats on this vehicle- I have race car/show car insurance which means I am exempt on emissions. My question is that after I installed new sensor, why would I be getting a "false lean" reading?? If the plugs were fouled wouldn't that creat a rich setting? Maybe im wrong or just haven't played with the car that much in the last year. If I replace the plugs, think this might help?

[Joe 1320]

I'm not sure what you've done, but here's the way it should be:

a 97 LT1 uses an OBDII program which requires 2 oxygen sensors, (one in each bank prior to the cats) and one O2 sensor after each cat as an effeciency monitor. fuel mixture readings are taken from the primary sensors, catalyst effeceincy is monitors from the secondary sensors.

What have you done to the computer?

where is the other 02 sensor harness connector?

If all you've done is the bolt on parts, put sims on the secondaries and run one 02 sensor on one bank, I'm not suprised it runs like crap.

[Injuneer]

When I said "02", I was referring to 1. I have long tube headers and only 1 O2 on right bank. I have sims on or where post cat would be.

Did you read what I posted? Your PCM requires a pre-cat O2 sensor on each bank of the engine to control the A/F ratio. Why would you not have a pre-cat O2 sensor in the left bank? If you believed that the leaded fuel ruined your right bank O2 sensor, why would you not feel the same thing happened to the left bank O2 sensor?

My question is that after I installed new sensor, why would I be getting a "false lean" reading?? If the plugs were fouled wouldn't that creat a rich setting? Maybe im wrong or just haven't played with the car that much in the last year. If I replace the plugs, think this might help?

Did you even read what I posted? I explained step-by-step why you got the results you did. It's all there in black and white. Fouled plugs cause misfire. Misfires cause air to leave the cylinder in the exhaust. The O2 sensor "sees" the air blowing out of the cylinders that are misfiring, and tells the PCM the engine is running lean. This is a "false" lean condition. The PCM adds extra fuel to richen it up, but its adding fuel to an A/F mixture that isn't really lean, and continuing to foul the plugs.

Yes... if fouled plugs are causing it to run excessively rich, replacing the plugs it required.

[Wild Willy]

I agree with most of what was said, with one question- if a plug is mis-firing, wouldn't all the unburned hydrocarbons make the O2 sensor see too much fuel, and think "rich" rather than lean? Seems like the computer response to running rich and/or not burning fuel (misfires) would be to lean out things, making an even worse situation- detonation or burning exhaust valves- at what point will the computer default into 'table' mode, open loop where it works on what 'shold be' happening, rather than reacting to sensor data?

[Craig 94 TA GT]

O2s read only that - oxygen. That is why the oxygen coming from the cylinder is making it think it's running lean. I think it solely relies on oxygen content.

[Injuneer]

I agree with most of what was said, with one question- if a plug is mis-firing, wouldn't all the unburned hydrocarbons make the O2 sensor see too much fuel, and think "rich" rather than lean? Seems like the computer response to running rich and/or not burning fuel (misfires) would be to lean out things, making an even worse situation- detonation or burning exhaust valves- at what point will the computer default into 'table' mode, open loop where it works on what 'shold be' happening, rather than reacting to sensor data?

It's an O2 SENSOR. It can only "see" oxygen. It can not tell what else is in the exhaust gas. When you correctly burn hydrocarbon fuel and air, there is very little oxygen left over. The O2 sensor is looking for very tiny amounts. If it sees a big gulp of air that is passing through the cylinder WITHOUT being consumed in the combustion process, it can only come to the conclusion that the combustion process is VERY lean.

If the O2 sensor could see the hydrocarbon components in the exhaust, it might come to a different conclusion, but it can't see anything but OXYGEN. It has no way of measuring anything other than oxygen.

The sensor is a zirconium thimble, that has ambient air on the outside, and the exhaust gas on the inside. The thimble develops a voltage based on the difference between the partial pressure (aka mole fraction) of the oxygen in the exhaust gas, and the partial pressure of the oxygen in ambient air. Even if the O2 was only 1%, and the other 99% of the exhaust was gasoline, it would still read "lean".

As long as the O2 sensor is putting out a signal that makes sense, the PCM will continue to believe it. Once the PCM sees numbers that go beyond the acceptable limits (stationary readings, infrequent "switching", long term fuel corrections outside acceptable limits -e.g +25%, -15% -, etc.) it will either disregard the sensor, or continue to believe it but set a code/SES light, warning you that something appears to be screwed up.

That's why OBD-II flashes the SES light for misfires. You are running the risk of serious damage to the catalytic converter. The resulting excessively rich exhaust will cause the fuel to collect and burn on the converter substrate, causing it to melt. While the OBD-II diagnostics are primarily concerned with emissions, the warning also indicates that you have a chance of damaging the engine by washing the lubrication off the cylinder walls with the excessively rich mixture.

[Brian P]

You know, I feel like a complete moron..

The problem is that I store my vehicle at folks house. I have a 2yr old and rarely keep my car at my house. I have a 2 1/2 car garage but my daily driver (01 blazer xtreme, blown and sprayed) on one side and wifes vehicle on other. I have not worked on my car since last season and I was in a frantic hurry to get that race gas out, put some regular (93 oct) in the tank. I was told to just replace "O2" sensor as in 1. Now that I think about it.... the sensor that was replaced was the right bank and which is located on the collector of the header. I didn't stop to think about the left bank, problem is I bet I missed it possibly because maybe it was located in a higher position maybe closer to primaries?? I DO NOT have cats on vehicle- the system came w/ them but I installed dumps on either side. The headers are from FINISH LINE PERFORMANCE which is located in Naperville, illinois. They are long tube if that helps. I have post cat sims. I really appreciate the help from all of you and keep it coming. I really hat replacing plugs but looks like I have 1 more O2 and 8 plugs to go. dammit

[Wild Willy]

Yeah, great bunch in here- I think collectively the years of experience here would go back before the steam locomotive-;>)

Almost anything you can think of, someone here has been there, done that- - Good luck with the truck- When you putting an LSX engine in it?