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After ECM reset great power-performance for about 30-minutes

US octane ratings are figured by taking research and method octane ratings and averaging the two, I have no idea how that correlates to European figures, I also don’t know if your Corsica is the same as the one sold here.

Most gas sold here comes in 87, 89, and 91 octane with about 90 % of our cars being able to use regular (87 uctane),

Rebooting the computer can be a sign that the computer is bad. Although mine was on an 85 car, it doesn’t mean your PCM isn’t also out to lunch. That PCM was only $100. Yours may be more expensive. I don’t believe that changing sensors will fix the issue.

Some sensors can be eroded badly or go bad with age, so feel free to keep trying.

It correlates to a 4 to 6 point lower octane number in the US than elsewhere. So 92 octane over there would be around 87 octane here.

Hello everyone, just want to say Im in California, and camped-toured-visited CANADA Calgary and Bamff National Park and used their gasoline that was far more superior to anything available in California, the next best gasoline was in Colorado-Idaho-Montana blends with highest octane available being 93, I never bought anything less than the best available gasoline for V6 3.1L Corsica and was able to get 34++ MPG with conservative driving and cruise-control 63MPH on freeways, boring but I was sight seeing so not a problem going mere 63MPH and nearly everyone “passing” going faster on freeways… In Europe I was only passenger as other people were driving, but same strong gasoline there as well as in Canada… -tibor

You seem to have convinced yourself that wasting money on fuel is a good thing. Your type of driving should have the same mileage results with regular 87 which is what your Corsica was designed for. Your statement about performing like a former police car is puzzling. Not saying your are wrong but I have never thought the Corsica was used for that .

About the part that great power after reset with your driving style why does that matter. Does the vehicle seem fine after 30 minutes to anyone else.

Oh, well if we’re talking US octane numbers then the others are right. You wasted your money. Premium is not “better” than regular gas any more than soap is better than shampoo. Soap is meant for cleaning skin. Shampoo is meant for cleaning hair.

Premium is meant for engines that require it. Regular is meant for engines that do not. The quality is the same, the only difference is that premium will not burn as readily as regular, which means high-compression environments won’t make it explode too early and damage things.

Hello, and thanks to everyone for continnued input on the seemingly loss of power of car after mere 30 minutes of ECM reset, or as it may be as it “learns”, starta out very nice and performance oriented then settles into relatively weak fuel-air mixture profile… currently suspecting inchoherent engine operating temperature data sending to ECM onbiard 1994 computer

(on a separate question, this computer trouble codes cannot be read at all because it is neither version 2.0 or older version 1.0 it is something in between like a 1.5 and NO-ONE has a way to get trouble codes out of the ECM computer… so any ideas on that would be fantastic!)

… so currently Im very interested in finding out what the OHM readings should be for y three different engine operating temperature sensors, and I want to compare those stats to actual OHM readings both cold (45f) and normal operating temperatures for the engine… thank you for everyone for the help, advice, and assistance given here!

Also my previous vehicle;

on this vehicle (1991 Superchief 454ci Tonawanda engine) it did not mater to much the quality of gasoline for it was a low compression engine, but the current 3.1L V6 chevy engine performs much better on higher octane slower burning non-knocking non-valve-noise-causing better gasoline… and I always by Chevron-Texaco-Phillips_66-Shell type expensive gasoline for the car…


If a car’s performance gets better right after an ECU reset and then drops, it indicates that the ECU is adjusting parameter(s) based on bad sensor inputs. As an example, if it thinks the car is running lean, and introduces more fuel, but the car actually wasn’t running lean, then now the ECU is making it run rich and reducing performance.

Please refer to the following for pulling your trouble codes:


I ordered parts today, two temp-sensor-sender and an O2 sensor, I will let everyone know if they solve the apparent power loss problem after a mere 30m of ECM reset, … thanks everyone for all the input!

It’s possible for two different temperature sensors in a car to have different ohm readings at the same temperature. It just depends on for what purpose they are designed. One might be 5,000 ohms at 20 deg C and the other might be 10,000 ohms. I’ve had difficulty finding the temperature vs ohm chart for my Corolla’s ECT sensor. Believe it or not, that chart appears nowhere in the Toyota factory service manual. I finally found the chart in an aftermarket manual, Haynes I think it was.

Sounds like you have a good plan there. I’m guessing the problem is either a faulty thermostat or O2 sensor. The engine performs under different operating parameters when it is cold. That’s called “open loop” operation. In open-loop the MAF or MAP is mostly what decides the amount of gas to inject. The O2 sensor is ignored in open loop mode. when it warms up though it enters “closed loop” operation, and then the fuel air mixture is controlled by the pre-cat O2 sensor, in conjunction with the MAF or MAP.

If you’ve done any recent repairs using RTV (silicone) sealant that might be the problem, as the fumes from that can quickly contaminate O2 sensors. You should also check your engine diagnostic codes stored in computer memory for clues.