I just purchased a 98 F150 4.6 with 77k from a friend. The check engine light was on and I had it checked and was told it was O2 sensor. I was told this light was on for approx 1.5 years. I purchased 2 new and installed them. Prior to replacing them the truck ran a little sluggish and would knock bad during hard excelleration.

I replaced both front sensors, reset the check engine light. That was the only thing done. I restart the truck and it had really bad hesitation when you step on the gas. Figured it just needed to relearn and drove it around the block a couple times. The hesitation got better, but still was really bad. Decided to take it onto the highway and this is where it gets interesting. Once you get past 20mph or so it runs ok, then I got up to 60-70 and ok, but then all of a sudden, the truck starts to die out like it wants to shut off, but doesn't and no matter what, starts to slow down to approx. 40-45 and sputtering all the time. I pulled off to the shoulder and tried again. Sometimes it will go above 40-45 and then die down again and sometimes it will get to 40-45 and not go any faster.

The check engine light hasn't returned, but its running really bad. Before I start replacing things, I was hoping someone would point me in the right direction. I am going to replace the plugs and wires and clean the MAF, but anything else I should check?

Thanks in advance.

 

Fuel filter

 

Thanks for the help, but it ended up being the MAF.....cleaned it and it runs like a champ