Ok, this is a major problem-o that im having with my 1997 ford f150 xlt. When I get the cheapest grade of gasoline, after running it through most of the tank, my truck begins to run real funny. Like its having trouble pumping the gas through thr engine. It ususally shakes a little at high speeds, then goes away after a few seconds. 10-20 seconds, but re-occurrs often. Also, when it does this my check engine light will flash and then go on, and stay on. Now when I use up all the crappy gas and put a better grade in it, which it is used to, the engine runs smoothly and the check engine light goes off. This has happened to me twice now and i havent found out how to solve the problem. It usually solves itself, but thats too good to be true! And it cant be a good thing to keep doing. The obvious solution is to get better gas, yes, but whats going on cant be normal. Please HELP!!!!! M.G.

 

Try changing out the Fuel Filter... it could help you with low-grade gas. Also, try resetting your engine computer. The comp may have set the timing too far back, and that can cause pre-ignition. Do you have a chip? Check the connection if you do.

Hope this helps
-Flea

 

If I bought gas from a station and it did that to my truck, I would never go there again.
There are plenty of gas stations around. Stay away from that one.

 

I am having the same problem and I already changed the fuel filter. How do you reset the computer.

 

Take an 8mm socket or wrench and loosen the positive or negative cable from the battery (no need to both). Turn your headlights on for at least 5 minutes after disconnecting the battery (drains the residual power). Then reconnect the battery, and that should reset your PCM. Make sure you don't forget to turn your lights back off. (Did that once and woke up to a dead battery.)

 

DON'T disconnect the positive cable! Only the Neg cable first!

have you used a gas dryer? Cheap gas sometimes has a lot of water in it which can cause what you are talking about. Try a few bottles. (Isopropyl based dry gas only!!)

other than that stay away from cheap gas. If you ment cheap and not low octane.

 

I am not sure about your truck year but with my 92 mine did that and I replaced the oxygen sensor.