I wasnt sure where to put this, its not comptuer related. does anyone know anything about engine misfires or such? Our 2003 Ford Expedition with 4.6L V8 Triton, with an Automatic tranny. Yesterday, our truck was at ~1/8 tank, filled with Regular from BJs, then put some HEET Drygas in while it was running. this morning it was fine, this afternoon, my mom said the engine light came on, and it was running really really rough. She said on a bridge, it started flashing, which means Engine misfire. but it hasnt done it since, though the "Service Engine soon" light is staying on, and it rusn rough. We managed to get in 6 gallons of Mid grade 89ppm octane Gasoline. I have revved it up, repeatedly, shut it off and started it again and again. It seems to have pretty bad shaking around 1500RPM but higher and lower are a bit steadier. above 2500RPM no shaking at all, apart from normal engine vibration. Trying to get a Scanner. I think either the Drygas is setting off the O2 sensor, and is messing the ECU up, and messing hte fuel/air mixture up. I have it pretty much narrowed down to O2 sensor, or a Engine Misfire. Any ideas? Mom really doesnt want to take it in, since it only has 1 payment left on it.

Mom is going out of her mind because we have to do a 2 hour drive down to manchester NH later to pick up my grandmother.

Sadly, reading your OP, it would seem that you already know far more about the combustion engine than I do......

Check the vaccum lines to make sure all are connected properlyand there are no broken hoses. Also make sure the petrol/gas cap is tight. I know that sounds odd AW_3_3 but I've seen it happen with these newer vehicles.

LC

It's a FORD! That's half your problem!

My 1992 Dodge Dakota has no O2 sensor and it runs fine. Gas mileage suffers a tad bit and I will blast out a dark cloud of black smoke when running over 2000 RPM, but that does not bother me at all. I use whatever gas is cheapest, which is usually 91 Octane with 10% Ethanol around here in the midwest.
Changed your spark plugs lately? Made sure that the power cables are on the correct spark to begin with?

hey, we happen to love ford, and this is the first problems we have had with it. It is only 5 years old, and has only 40,000 Miles on it (we lived in hawaii for 3 of those years) its not the spark plugs, i know that much. It did the misfire thing twice more, generally going uphill, just after getting on the highway. We found a way to make it run better, and suck down more of the potentially bad gas, turn OD off and that raises the RPM to about 2600, well out of the problem range. But at slower speeds, generally between 1100 and 1700 RPM, it seems to have problems.