I've got a 98 F150 4x4 - 99,500miles. Truck starts and idles fine but when you hit the accelerator the RPM dives off and then recovers slowly. You can hear a loud sucking noise coming from under the hood when you hit the gas. The truck has absolutely no power any more - it also hits about 40-50mph on the highway and will not accelerate beyond even with your foot to the floor. If you let up on the gas and get on it again at around the 40-50mph markit will straighten out and continue to accelerate - still with verylimited power. Sucker feels like I'm towing a led sled all the time. Took the truck in to the local Champion Auto and they scanned it - says a misfire on cyl.#3 and store says O2 sensors need changed. I've changed I don't know how many O2 sensors over the years and that never has seemed to be the problem so a little skeptical. I had someone tell me mass airflow and another tell me cat. converter maybe plugged????? Any ideas...thanks.

 

what motor does it have

 

Sorry - truck has a 4.6L

 

If your catalytic convertor was clogged, usually they get red hot or v ery near red hot. Youmay be able to look under the truck after running it to see.

 

My 98 had the CEL on, was told it was the O2 sensor so I replaced them. Light came back on, ended up being the MAF sensor. Once replaced all was good and the truck has been running with no issues for months

 

What was the codes that the parts store read? If they aretrying to sell you O2 sensors, then it probably because you either got lean or rich condition readings. From your description, I would say lean. I would clean the "hot wire" on the MAF sensor with some choke cleaner and let it air dry. This sensor compares voltage on 2 wires to detemine how much air is coming into the engine. If the wires are dirty, it cannot see how much air and causes it to run lean. I have never seen an O2 sensor cause a drivability problem, just a check engine lite, because it is the tattletale of the system, not an actuator. People who do not understand how systems work will go with the code and not the cause of the code. That is why so many unnecessary parts are put on cars. Parts stores are in buisness to sell parts, not fix them.

 

You might also check the fuel filter and fuel pressure.