I have a 85' F150 4x4 with the 4.9 in it. I recently had the catyaltic converters cut off now the thing is backfireing badly... blew the muffler inhalf . I've plugged the exhaust backflow pipe. I've also changed plugs, plug wires, distributor cap, and rotor button. It runs smoothly until it warms up. What could be causing it?

 

Check for a vacuum leak. It sounds like a lean miss to me.

 

Thanks! I'll look into that. Do you have any suggestions on where to start looking, an area you would think could be the most likely area to cause such a leak besides the obvious carb. area?

 

I just noticed I posted this in the wrong area......Sorry about that I'll put it in the right one now.

 

With the truck running spray carb cleaner around the intake and carb base see if the engine speeds up.

 

I'll give that a try Thank you. I think I figured out what's happening though... I sprayed degreaser on it the other day and then risned it with water.... the wires going into the distributor were wrapped in foil which was loaded with oil, grease, and yes water. I wiped them off really good and sprayed them down with good ole' WD-40 and it seems to be running better than ever. I'll take them back apart in a day or so and do the same thing again and we'll see I'll keep everyone here updated on progress.

 

Problem solved....It turned out to be the water on the ignition mudule plug that was causing all the troubles. She's running stronger everyday. Just thought I'd let everyone know and say thanks for the help and input given