I have a 94 f150 super cab with 270,000 miles. Over the past few months it has been getting weaker and mpg has been going down. I have checked the fuel pressure (32-33 lbs running), EGR system (valve, sensor, vacuum lines, air pump, check valves, etc). Engine starts fine and I have attached a vaccum gauge to it which reads 20" at idle and stays there even when revving up to 3000 to 4000 rpms. Once I put it in drive and try to accelerate it drops to 0" and the engine shudders and misses and won't get up to speed. Has anyone had this problem before? My next thought is a plugged catalytic converter, but would I be able to maintain 20" of vacuum at 3000 rpms in Park if it was?

 

You can do a rough and ready test for a plugged cat. With the engine cold, start the engine and let it idle. Now get under the truck and with your hand, feel the temperature of the inlet pipe to the cat. Now feel the temperature of the outlet pipe. If the cat is good the temperatures should be similar. If the outlet is much cooler than the inlet there is a good chance that the cat is bad.

 

I also recall reading to use one of those cheapie infrared heat guns to measure the incoming and outgoing temperatures. A good converter will measure within 100 degrees Fahrenheit of each other.

 

Cool. I will give that a try.